Elastomeric or liquid waterproofing membranes are one of the most convenient methods of waterproofing shower walls before installing tile. These membranes consist of products such as Custom Building Products’ Redgard and Laticrete’s Hydrobarrier and Hydroban and Mapei’s Aquadefense. I will refer to all the membranes as Redgard for the purposes of this post, but they all work nearly the same way.
These materials can be installed with a regular paint brush, paint roller, trowel, or even sprayed on. They are applied to your shower walls then tile is installed directly onto it. When I use these products I always use a cement-based backerboard as the wall substrate without a plastic vapor barrier.
It is imperative that you do not install plastic behind your walls since this would create two waterproof membranes with your substrate between them. Having two barriers this close together leaves open the chance of trapping moisture between them with no way for it to evaporate. This may lead to mold.You must also tape the backerboard seams with fiberglass mesh drywall tape.
The easiest way I have found to install Redgard is, after the walls are prepped properly, start with a paint brush and thoroughly coat all the corners and angles. The membranes are more the consistancy of pudding than paint so don’t be afraid to scoop it out to spread it. You should be used to it after a few minutes.
After all the corners are coated I use a paint roller and pan to cover the walls. Redgard is bright pink – I mean pepto-bismol pink, it almost glows in the dark. This is useful in that when it is dry it turns dark red. The other membranes are similar. Laticrete’s Hydroban, for instance, goes on light green and dries forest green.
Just thoroughly coat the entire inside of your shower until the whole thing is bright pink – enough so it can be seen from space. That’s it – go have an adult beverage until it dries. You must then do a whole second coat the same way. Make sure the first coat has fully changed color before applying the second coat. If you are using a roller Custom (the company that makes redgard) recommends that you roll on the first coat horizontally and the second coat vertically to ensure full coverage. (Thanks for that Davis)
Most of the product specifications for these materials state two coats to be sufficient, and it probably is. I normally use three coats. I’m weird like that. Unless you have a steam shower or something similar, two coats would probably be enough. It’s up to you.
These products shrink a bit as they dry so you must make sure that it has not shrunk enough to create holes or voids in places such as corners and seams. You need a full coating for the product to be effective. When you are finished you should let the walls completely dry for a day before tiling.
Your tile can then be installed directly onto your walls over the membrane with a proper thinset mortar. When these products set they will create a rubber-like coating on your walls that is waterproof. When used on shower walls it is a (relatively) quick, effective water barrier for your installation.
These products can also be used as waterproofing on your shower pans in leiu of a regular pan membrane. Make sure your specific product includes specifications for this application if you choose to do that. Check the respective website for your particular product. I do know you can do this with Redgard, Aquadefense, and Hydroban.
I also use these products for main or additional waterproofing on things like shower niches and concrete wall in basements, places where it is difficult to have a plastic vapor membrane behind the backerboards. Basically any place that does not have waterproofing between the tile and shower framing. I always have Redgard with me. The versatility of these products make them a integral part of my shower waterproofing toolbox.
The only drawback for these products, if you choose to look at it that way, would be the price. They are a bit expensive. You may be able to get better prices by ordering online but make sure you take shipping costs into consideration. You can get a gallon of Redgard online for about $45.00 plus shipping. That should be enough to do a regular tub surround. That is a five foot back wall with two 3 foot side walls. For larger showers you can also get a 3.5 gallon bucket.
Make sure to check the website for your product, they have a load of information for them. As always, if you have any questions feel free to leave a comment for me.
Need More Information?
I now have manuals describing the complete process for you from bare wall studs all the way up to a completely waterproof shower substrate for your tile. If you are tiling your floor and walls and using a liquid membrane you can find that one here: Liquid Topical Waterproofing Membranes for Floors and Walls.
If you are just tiling around your tub or pre-formed shower base you can find that manual here: Liquid Topical Waterproofing Membranes for Shower Walls.
I’m building an backyard pondless waterfall out of cinder block. I plan on covering the 4 shelves, that the water will cascade down on, with travertine and use veneer stack stone on the sides. Would it be a good idea to primer the entire area with Redgard and then a few coats of Redgard before motar/thin set for stone? Also, should a coat of concrete adhesive be applied to the cinder block before? thanks for any help
Hey Dave,
If the entire structure is made from cinder blocks there really is no reason to waterproof the shelves unless you want to absolutely control where every drop of water goes. The blocks will become saturated if not waterproofed but will make absolutely no difference unless there is something beneath or behind them you want to keep dry. If you do waterproof them it is always easier to skim-coat with thinset first – it will use less redgard since it won’t need to fill the open pores in the cinder blocks.
thanks for the quick reply and answer!
Hi, I’m re-doing a tub surround which will be eventually tiled. I’m planning on using DensShield as the backer. I’ve now been given two options:
1. Tape the seams, fill with a quick-drying Durabond mud. Coat all seams with Redgard. Tile using a thin-set mortar.
2. Use Schluter’s kerdi system (on top of the DensShield) and tile as per the Schluter instructions.
My question is, wouldn’t the kerdi system be a bit of overkill as the DensShield already incorporates a vapour barrier? Would there be any problem using kerdi overtop of DensShield? Similarly, would using Redgard on top of DensShield cause any problems, given that it’s kind of duplicating the vapour barrier purpose?
Thanks so much for your advice and thoughts!
Hi Brian,
Not sure who has given you these two options but both of them are (mostly) incorrect. While both choice 1 and 2 can be used to fully waterproof the denshield neither is actually necessary.
Denshield is a gypsum-based core with a waterproofed facing on the sheets. This means that the entire face of the sheets are already waterproof. The only areas you need to be concerned with are the seams of the denshield and the corners of the shower. Per Denshield instructions all that is required is that these areas be siliconed to seal them as you install the denshield on the walls.
There really is no need for an additional waterproofing membrane over any part of the denshield – it’s already waterproof. Mixing products in this manner may actually cause more problems than it will solve. Installing kerdi over denshield is not only expensive – it’s overkill and if you do not use the proper thinset and get correct coverage you may actually compromise the waterproofing or create an area in which water may build up. I honestly do not know if redgard to denshield would create a waterproof seam or if that would eventually become compromised due to the compatibility of the products.
Hi Roger,
Thanks so much for your response. I agree that installing kerdi over the denshield is overkill, as I originally suspected. I appreciate the confirmation!
And now I’m wondering what you would recommend for the ceiling above the tub (it’s a dropped/alcove ceiling so at about 7′ high) – DensShield and then skim coat it to be able to paint it? I’ve read it can be a bit difficult to skim-coat it. Or would the moisture-resistant (Humitek) board be ok? I’ve been getting opinions that either would be ok.
If Denshield is used on the ceiling , would you first silcone the joint (wall to ceiling), then use the fibreglass tape with joint-compound mud to cover the tape (for the ceiling to be painted, not tiled) ?
Similarly, if moisture-resistant board on ceiling, finish the joint (wall to ceiling) first with silicone, then tape the joint (paper or metal inside-corner?) and mud as well ?
I apologize for these basic questions but with all the various opinions on what to do and not to do, it can be quite intimidating as to the proper procedure. Thanks again for your help!
Hey Brian,
You can use denshield on the ceiling if you choose to do so. There really is no need to silicone the joint up that high but you can if you want to. Anywhere around a shower always use a mesh drywall tape – the metal rusts. You can skim it with thinset or drywall mud. If you use the mud use the powdered that you mix with water – the stuff in the bucket will soften and fall apart when subjected to moisture. You can paint over thinset as well should you choose to use that.
I am not familiar with Humitek board – never heard of it so I really can’t speak to the use of it in that application.
Hi Roger,
Good point about the metal rusting around the shower area – I noticed that when ripping out the previous enclosure. I’ve got an outside corner though right at the edge of the tub/enclosure (tub’s set in an alcove) and the tiles would have to come right to the edge of the corner. What would you do for that corner? Plastic corner? Or…?
Humitek seems to be what has replace ‘green-board’, at least here in Vancouver. Here’s a little bit about it from the manufacturer’s website…
SHEETROCK® Humitek™ Gypsum Panels are moisture and mould panels that are ideal for use in areas of a building that have limited humidity control such as bathrooms, kitchens, laundry rooms, basements and garages. Sheetrock® Humitek™ Gypsum Panels are easy to work with, provide a smooth surface and offer fire-resistance.
They have a non-combustible, moisture and mould-resistant gypsum core with a moisture resistant, 100% recycled, blue face paper. The product scores and snaps easily and is UL Classified and ULC listed for fire resistance, surface burning characteristics and non-combustibility.
Features and Benefits
* Superior moisture and mould resistance versus regular gypsum panels
* Ideal for use in areas with limited humidity control
* Score and snap quickly and easily
I’m going to use it throughout the rest of the bathroom, with DensShield around the tub enclosure. So just wondering if you’d use ths Humitek board for the ceiling over the tub or better to stick with DensShield there too.
I’ve been reading some of the other threads and really appreciate you sharing your expertise. Thanks again!
Hey Brian,
I absolutely love the plastic corners – they work great so I would go ahead and utilize that on that particular corner. As far as the humitek I don’t see any reason not to use it if you’re comfortable with it. I don’t tell people to use something I have never used nor seen. So that particular call would need to be entirely left to your comfort level.
What I can tell you is that green board, in my opinion, was one of the worst products ever to hit the market. It had it’s uses and places but the overblown claims made by the marketing as well as the obvious lack of field testing led to many, many failed showers because people trusted the claims made by the marketing concerning the water resistance of the product. I hate it.
So, with that typed, If the humitek is something you’d feel comfortable using then do it. I don’t know if it will work or not – it may be just fine. The denshield, on the other hand, I know will work just fine. Entirely up to you… I’m a lot of help, huh?
Hi Roger,
Thanks again for your thoughts. I’ve finally got all the drywall up in the bathroom with Denshield for the tub surround. It’s been a slow process but that’s what happens when you take a vacation to France in the middle of it all!
Regarding using the plastic corner for the outside corner of the tub surround where the tiles will come right up to that edge, with the other side of the corner being a finished wall without tiles, how would you finish that corner? Would you put thinset over the corner bead on the tile side and joint compound on the non-tiled wall? Or could you put joint compound, such as Durabond, on both sides of the corner bead – would that be strong enough to tile on top of?
I read a suggestion somewhere to use fiberglass mesh tape over the corner and finish with Durabond which this fellow thought it should then be a strong enough surface for tiling. What do you think? I like the idea of using a plastic corner but not sure what’s the best way of then tiling over top of the one side of the corner bead.
Thanks again!
Brian
Hey Brian,
I usually use thinset on the wet side of the corner bead. You can use joint compound as long as it is the powdered type that you mix with water and not the stuff in the bucket. The difference being that the powdered stuff cures through a chemical process and is not affected by moisture whereas the stuff in the bucket will disintegrate. Of course if you use thinset you don’t have to worry about any of that.
The instructions say to wait 28 days before installing redgard over concrete. That seems a very long time, and I can’t go without a shower/bath for a month. Is that really necessary? How soon could the redgard be added over concrete?
clarify: only thin cement stucco on the walls and enough to create a sloped bed on the bath.
Hi Cat,
The 28 day requirement refers to full cure time (essentially) for normal concrete and only applies to a concrete slab such as for a basement, porch, etc. They do not mean a skim coat on the walls nor a shower mud deck. I do hope you are not actually using stucco on the walls??? Unsure why you would be doing that. If you are referring to a skim coat of thinset over something like brick on the walls then okay – no need for the 28 days. That is what you mean – right?
Thanks for the information. I have a couple of questions that I didn’t see answered anywhere:
1. If I want to use Redgard to cover my Hardibacker walls and my presloped mud pan, do I just tape all the seams (including the seam between the bottom of the walls and the preslope) with fiberglass mesh, then Redgard over everything? Or is there another way to handle the wall-floor seam?
2. If I use Redgard as my shower pan liner, will I need some sort of fiberglass mesh reinforcement around my three-part Home Depot clamping drain?
Thanks in advance.
Hi Dave,
1) Yes, you need to tape all the seams as well as all the changes of plane. That is just areas where the plane changes direction such as corners, wall to floor seam, etc.
2) Yes, you do need fiberglass reinforcement around your drain as well. With a topical membrane, however, you only need one mud bed – not a pre-slope, the membrane, then the mud bed. It is simply one mud deck with the membrane to waterproof it. Around your drain you will need to leave a ‘divot’. If you read my response to Robert in the comments below which I wrote on April 29, 2010 at 8:35 pm it will explain in more detail the method I’m talking about.
While you can do a pre-slope, paint on your membrane, then install a mud deck over it for your tile there really is no reason to do all that and it essentially negates a lot of the advantages of using a topical waterproofing. Read my response to Robert below and check out that link there – it will explain just about everything you want about liquid membranes.
The back wall of my shower has 2 layers of drywall (removed now) in order to bring the wall out to meet the shower pans lip. Should I install one layer of greenboard and then hardi or two layers of 1/2 hardi on the wall? should any adhesive be used between the two layers?
Thanks
Hi Mike,
Yes, you can use 1 layer of REGULAR drywall (not greenboard) then 1/2″ hardi to build it out to where you need it. This is, of course, assuming that you are using a topical waterproofing like redgard. If not you need two layers of hardi or other similar dimensionally stable board behind your tile. And no, don’t use any adhesive between the layers, just screw them to the wall studs. Adhesive will simply add voids between the layers.
Very interesting Post. One question, relative to the thinset for the tile after the redgard is on. Is there a specific type that should be used? I’m using a 12 inch tile on the walls of the shower. Will a modified thinset work, if I allow it to cure for say 4 days before grouting?
Hey Mike,
Modified thinset will work just fine over redgard. You don’t need to wait more than about 24 hours to grout unless you are using larger tiles (over 12″ square).
Quick question regarding the issue of using two waterproof barriers, say, plastic and Redguard. If the plastic is behind the Hardibacker, and the Redguard is on the surface… where does the water come from so that it can become trapped between them? Wouldn’t it have to breach one of the two barriers ( assuming they are done properly )? I’ve just read this multiple times and it makes no sense, to me. And if you have water behind your Redguard, for whatever reason, wouldn’t you rather have your Hardibacker develop mold, versus your studs ( ie structure of the building )? In my experience, it’s a lot easier to replace the former, than the latter.
Thanks.
Hi David,
The water would be present from the moisture in the hardi itself, vapor from wood drying, various places that normal vapor is periodically present. With only the redgard this vapor will dissipate into the wall cavity eventually without affecting the studs at all. With only the vapor barrier this moisture will eventually be turned back into water and flushed down into the shower basin as water is cycled through the shower.
With both the redgard and moisture barrier this vapor has no place to dissipate. It will not negatively affect the dimensional stability of the hardi or your shower but it becomes a moisture source for mold. Mold needs moisture, darkness, and a food source. Trapping this moisture between two waterproof barriers creates a perfect environment for mold.
If you place a vapor barrier over the studs you take away the ability of vapor to dissipate. This vapor will not cause mold on your hardibacker or your studs as long as it can dissipate – placing plastic over your studs prevents that from happening.
Thanks Roger. I understand that theory, but in practice there seem to be problems with it. First of all, if the only thing between the redguard and the vapor barrier is Hardibacker, that is far from a ‘perfect environment’ for mold. It won’t be very wet, just the slight amount of moisture normally present on, basically, everything. There also won’t be any food, since the Hardibacker is mold-proof, and not edible to them anyway. It will be dark, that’s for sure.
Also, there’s this idea that with just one layer of barrier, the moisture will evaporate… but that will only happen if the air is relatively warm and dry ( giving the moisture somewhere to evaporate to ). That may or may not describe the air inside your walls. Seems like a crapshoot, at best, to me. More to the point, it seems like a worse bet than getting substantial mold to grow on (relatively) dry Hardiboard.
Thanks for taking the time to reply. ‘Ppreciate it.
Hi David,
I understand your theory, in my practice, however, there seem to be problems with it.
I started this blog as an information source for DIY’ers such as yourself to find current and acceptable standards and practices in the tile industry. What I’ve given you is exactly that. You can think it to death and it won’t change the FACT that if you have a vapor barrier and a topical waterproofing membrane in the same shower it will likely grow mold between those two barriers.
As far as hardiebacker being the only thing between those two barriers that is technically correct, however, the bottom of that wall is not sealed (even if it is directly against the concrete or wood) – nor is the top completely sealed. I have given you guidelines to properly build a shower – something I do every day – as well as advice on what not to do when you build that shower. A double vapor barrier is one of the things not to do. EVERY time I tear one out that is built like that it is moldy – every time. It is your shower – build it however you would like. Will it definitely grow mold if you use two barriers? Maybe – maybe not. Will it if you only use one correctly? Definitely not.
Don’t take my word for it – ask other professional tile contractors that know about such things. Here’s one place to start for you: JohnBridge.com All I do is document standard practices and warnings – what you choose to do with it is entirely up to you.
Thanks again, Roger. I’m already on John Bridge’s forum, but since this article is exactly on-topic, I thought I’d ask here.
Again, I understand _what_ the standard practice is, I was just asking _why_. Apparently, the answer is that people are more comfortable hoping for evaporation than betting against mold growing on treated concrete, where there is no food.
For the record, both of the bathrooms in my house were built with one barrier ( not by me ), and both were disgustingly moldly when I tore them out. So in my admittedly-limited experience, it is definitely possible to grow mold with just one barrier. I’m not trying to be argumentative, just adding two data points, and trying to explain why I’m curious about the SOP, since it didn’t work in my house.
When I tear out a shower with two moisture barriers it always has mold. If I tear one out that has been properly built with a topical membrane there is no mold. Depending on the construction of hardi with a vapor barrier behind it – there may or may not be mold.
Other people may be comfortable ‘hoping’ for evaporation – I’m not. If there is mold in every shower I tear out using two vapor barriers I will not build a shower in that manner. Hope has nothing to do with it. I don’t know the construction method of the two showers you tore out so I can’t speak to why it happened. But yes – it is possible if it is not properly constructed and maintained. I did not say it wasn’t possible – I said it wouldn’t grow if you only use one barrier correctly. I tear those out all the time, too (the incorrectly built ones.)
Did your showers have mastic in them? What type of backerboard did they have? There are many, many factors that can cause mold growth so without specific information it would be difficult to nail down why the SOP did not work in your two showers. What I can tell you definitively is that if you use only redgard and install it properly and your shower is maintained regularly there will be no mold growth. I can also tell you definitively that properly constructed and maintained showers do not grow mold – ever, and that topical membranes assist greatly with that.
Hope that helps. I was not trying to insinuate that you were being argumentative – didn’t even think it. On the other hand – I know I am, it’s in my nature.
Since you don’t seem to mind having a reasonable discussion on this topic, I hope you don’t mind my continuing that. I think we agree that it’s impossible to create or maintain a perfectly dry area… there will always be some level of moisture. Given that, we only have two choices to prevent mold; continually evaporate that moisture into a fresh air supply, or make sure no mold food supply exists. Is that fair to say?
If you aren’t simply hoping for evaporation, you must have some way to guarantee that the air in the wall cavity stays both dry and warm enough to constantly accept new moisture. How do you do that? For most bathrooms, that’s something like multiple 3.5x14x96″ spaces with no significant airflow. A few weeks or maybe months after you seal that space up, it’s going to reach 100% humidity. What then? No more evaporation, and plenty of food ( your studs ) and water for mold.
For reference, I’m in the middle of a shower project right now. I’m trying to decide how best to make sure I never ( again ) have to cut out and replace moldy studs. BTDT twice. If you can tell me how I can ensure an evaporation-friendly environment in my wall cavities, I’ll probably do it. Right now, I’m leaning towards two layers of waterproofing, and taking my chances that James Hardie isn’t lying about the ability of mold to grow on Hardibacker ( they claim it scores a ‘perfect’ result when subjected to industry mold tests ).
Finally, a couple quick questions just to confirm that I’m understanding your previous posts. You’ve torn out moldy Hardibacker ( the kind they sell now, with “Moldblock Technology”, whatever that is )? And second, what’s the oldest Redguard-ed shower you’ve torn out? Since you’re guaranteeing that correctly-applied Redguard won’t allow mold to grow, I’m guessing you’ve torn out a lot of them, and some must have been quite old, right?
Thanks again for the time.
It is impossible to create a perfectly dry area – anywhere in a house. There will always be moisture present in every wall cavity of your house. This completely normal ever-present moisture from vapor evaporating from the moisture in studs, vapor transmission from concrete (always present save for sealed concrete) and normal vapor transmissions from just about every building product. I’m talking here about any wall cavity in your house – it’s completely normal and that vapor eventually dissipates. This may happen quickly or slowly depending on the dryness and temperature of the air inside your wall cavity. But you don’t worry about tearing drywall out of your living room and finding moldy studs – not normally, anyway.
The point on which we are parting ways with the understanding of water containment, I think, is that you are considering the entire system and adding this ever-present moisture into the equation of your shower building. I, on the other hand, treat every shower absolutely the same as far as water containment. The moisture and vapor currently present in your wall cavity can be treated as a dry area in your living room – it should be built exactly the same. Save for the construction of a steam shower that cavity should remain identical whether it is in your living room or behind your shower wall.
When you build a shower it should be built as if it is a free-standing structure in the center of a room – follow me? Every ounce of water and moisture created by that shower should be 100% contained inside that shower. From the face of the waterproofing all the way to the drain is what I consider ‘inside the shower’. From your water source, which in this case should only be your shower head and/or tub spout, all the way back to whatever waterproofing layer you choose is what is actually ‘inside the shower’. Anything behind that waterproofing layer does not matter! If your shower is correctly waterproofed you don’t need to worry one iota about anything on the other side of your waterproofing layer – outside of the shower.
As long as your shower substrate is correctly waterproofed there will be absolutely no excess moisture entering your wall cavity whatsoever. That being the case your wall cavity behind your shower wall will grow mold about as well as your living room wall cavity. Zero excess moisture = zero chance for mold growth – correct?
If you choose hardi with a moisture barrier then ‘inside the shower’ would constitute everything from the moisture barrier out (toward the shower). Nothing behind that moisture barrier should receive any moisture at all. If you choose topical waterproofing – redgard – everything from the face of the redgard out (toward the shower) is ‘inside the shower’. Nothing behind the redgard is going to receive moisture. You should have no more moisture in the wall cavity behind your shower than anywhere else in your house.
The best thing you can do is use the redgard and ensure it is installed correctly and thickly enough. Given that you will have no problems. If you use two barriers you are simply adding a space behind your waterproofing layer which has the possibility of trapping moisture with no way for it to dissipate – why do that? Thinking about the free-standing shower in the middle of the room you are simply adding a layer which could cause problems with absolutely no benefit.
The advantage of topical membranes is that they allow less water penetration back into your wall. The barrier installed directly behind your tile layer prevents moisture beyond that point back into your wall. A normal moisture barrier behind hardi will allow hardi to be saturated before hitting the barrier. More standing or stagnant water inside your shower with that method. But! properly constructed it will not allow moisture back into your wall cavity either. The topical membranes are the best current method available given the allowance for the amount of water behind your tile before hitting a barrier – they simply allow less. Less moisture – better shower construction.
I have torn out moldy showers in which hardibacker was used – the mold was not feeding on the hardibacker itself. It was simply feeding on the wood, oils, stagnant water, etc. These showers were incorrectly built and allowed moisture and water behind the barrier (when it was present at all) and into the wall cavity where every item was available for mold survival and growth.
I have torn out two ‘redgard only’ showers – the oldest being about eleven years old – and once again they were simply built incorrectly without mesh reinforcement at plane changes. When used as the waterproofing for the pan there needs to be reinforcement at corners, etc. to maintain the waterproof integrity of the redgard. The parts of the shower which were not breached by water – the wall studs and substrate were in perfect condition – no mold or moisture at all. I have also torn out a nine-year-old redgard only shower which was being replaced simply because they wanted the design changed – not one ounce of moisture was present behind the redgarded hardi (short of what is normal in a wall cavity) and the studs were in pristine condition.
I have also torn out two showers in which redgard (one was actually hydro-ban) was used in conjunction with a vapor barrier. On one of these showers there was definitely mold present between the two barriers. Now I really don’t know what it was feeding on, it could have been the hardi or something that was present on the hardi – I don’t know. But I do know it was there and present up about a foot from the base of the wall between the barriers. The second was so badly built I honestly couldn’t tell you where the mold started nor on what it was feeding. But I do know that in that shower the mold was also present between the two separate barriers.
I have torn out a lot of showers – not a lot of topically waterproofed showers. Two main reasons I believe for this are that topical waterproofing for an entire shower is relatively new (as far as shower construction methods go) and the simple fact that it works – and works well.
Great – now you’ve got me babbling…
“When you build a shower it should be built as if it is a free-standing structure in the center of a room – follow me? Every ounce of water and moisture created by that shower should be 100% contained inside that shower.”
I think we’ve finally found the point where we diverge. It’s the ‘100% contained’ part above.
I looked up the specifications for Redguard ( permeance rating of .06 and water vapor transmission of .02 ), and see that it is about half as resistant to water vapor as Kraft paper. And since the Kraft-faced insulation I’ve seen hasn’t stopped moisture or mold, that doesn’t lead me to use terms like ‘100% contained’. If it did, I would certainly agree that one barrier is best. I can see that one barrier is often sufficient when you have some airflow through the walls.
Thanks again.
Hi Roger,
I have 2 questions about Redgard. 1) You say that you do prime for Hardibacker, do you prime for Durock? 2) The instructions say to put felt paper on if its not covered within 72 hours. It’s not exactly clear, but I think that’s if the application is outside. Is that correct?
Thank you for all your help.
Hi Jenn,
1) Yes, priming durock makes it much easier to install the subsequent layers.
2) Correct, those are instructions for outdoor applications only. It is simply to keep the Redgard in good shape before it is covered with tile if it will be exposed to outdoor elements such as sun, rain, and dogs with full bladders.
3) I did get the flat tire on my yak changed – thanks for the help.
Oh – Sorry, you only asked two questions, my bad…
First, i would like to thank you for your timely response to my question. As it appears to be very evident you are a tile craftsman that knows his stuff, i do not question your response to challenge your knowledge, but to more less fully understand the concept. As stated in your article, Redgard can be used for the shower pan, in which you would still want to use a sloped mud bed im assuming. If a shower were to be installed like that, there would be nothing under the mud bed, except felt which would be another form of moisture barrier. If the walls are coated to the top, and the tile is sealed, how is what Ive done any different than using Redgard for the membrane. Not trying to be a smart ass, just wanting to know the difference to either compound my worry of what ive done or ease my mind. Will using a sealer on the tile regularly help? It will be hard to get the tile man to change it as he is an older gentlemen that has been doing this for 40 years and he is helping me out price wise. I do not want to disrespect him even though ive all ready applied the redgard. Obviously, it seems like my framing will be safe from water as i have overkilled it on the waterproofing, and it is just the mold that will be the problem. Any other suggestions?
Thanks
Hey Robert,
I know you’re not being a smart ass.
The difference is with the drain. A regular three part clamping drain has the lower and upper flange between which the waterproof liner is clamped. On the bottom of the upper flange are weep holes. These are drainage access holes which allow water reaching the liner to run down into the drain. They are essentially openings in your drain. When using a liquid membrane as your waterproofing there is a ‘divot’ in the deck mud around the drain. It looks like someone left a mixing bowl around the drain when fabricating the mud bed. What this does is allows the surface of the shower floor to dip down from the top of the floor to the weep holes. At that point your membrane is applied and allowed to cure. After that the divot is filled in with deck mud.
Now, what this does is allow any water under the tile and grout to run down into the drain when it hits the redgard and any that saturates the mud in the divot will run down and into the weep holes. When you use a topical membrane you need to either use the kerdi drain (which is a one piece drain without weep holes) or allow the weep holes to function as they are designed to. The ‘divot method’ does the latter.
The only problem with coating the remaining surface of the shower with redgard is only the drain. Leaving the weep holes open between the two layers basically negates your waterproofing as water can run out of the weep holes and moisture will still saturate your mud bed. If you could or can chip out an inverse sphere around your drain all the way down to where the liner is clamped and the weep holes are located (about eight inches across or so) and then coat it with redgard, allow it to cure, then fill it in with deck mud it would work just fine and you shouldn’t have any problems with it. That would be the easiest solution at this point. There is a photo of the divot method (with hydroban – it’s blue) here: http://www.johnbridge.com/vbulletin/showpost.php?p=782400&postcount=44 and that particular thread is a good read about waterproofing with liquid membranes, it’s here: http://www.johnbridge.com/vbulletin/showthread.php?t=72403
Hope that helps.
My tile man has started on my shower and has built the pan. He has installed the liner directly to the floor level without building a slope. This has me a little worried so i have coated my mud bed that has been sloped completely to the drain with Redgard before the tile is installed. I have read the post about the two layers of membrane creating mold, but if i have completely covered my floor and 3 foot up the walls, will this still be a problem.
Hi Robert,
Unfortunately what you’ve done will do absolutely nothing to solve the problem. Any water getting behind the tile and grout above the redgard will still make its way down into the liner which, unfortunately, is flat on the floor. While there will not be nearly as much standing water in the bottom of the liner immediately, eventually there will be. Whether or not the mud bed is coated with redgard makes no difference in the production of mold in this case. The fact that water will be sitting in the bottom of the liner without any way to drain is what will cause mold. Coating it with redgard will simply prevent any of that water from evaporating.
And before you ask
using redgard all the way up the walls will only slow the process as well. See, the weep holes in the drain are open. These are holes that are beneath the mud bed and, in turn, beneath your redgard. So it will eventually get wet under there. The only way to prevent mold is to have a properly built shower. It seems your ’tile man’ has not done that.
You’re paying the bill – make him do that. If he cannot or does not know how, pay someone that does. I have photos of showers that did not have a pre-slope on the ‘flawed’ page so you can see what happens with improperly built showers. That is what you currently have. Sorry to sound like an ass but it needs to be done properly to prevent what you see on that page.
That was a good idea, though, I wish it would work for you. It may for a while but eventually it will fail.
When talking about priming before putting on the Redgard. What kind of product is used for the primer?
Hi Alan,
You actually use Redgard for the primer. Make a mixture of one part Redgard to three parts water and brush or roll that onto your backerboard. Cement backerboards are ‘thirsty’ and will suck the moisture out of anything placed on it such as Redgard or thinset. By using this mixture on your walls first it will allow the backerboard to suck the water out of it leaving the Redgard firmly bonded to your substrate. Any subsequent layers of Redgard will then go on correctly without prematurely being sucked dry.
I am planning on using redgard on remodel of bathroom shower walls . I just want to make sure I have the steps right. concrete board then redgard, do I add mesh on corners and all seams during 1st coat? Let dry then 2nd coat then the thinset when I’m ready to tile. I am planning on installing bench with granite any problems with redgard and thinset with this?
Hi Kelly,
The order of installation for Redgard with concrete board is: concrete board, then use tape and thinset on the seams, after that cures then you apply the 2 coats of Redgard, then tile. You need one large monolithic structure all locked together before you apply the redgard.
Depending on the size of your bench you may want to use an unmodified thinset for your granite top. A modified will work fine but it contains polymers which require air to cure. I would use an unmodified or allow a modified to cure for a couple of days before sealing everything up with silicone, etc.
I have a leak in the shower pan, which is covered with a tile floor. If I paint the tile with Redgard, will it stop the leaking.
Hi CHic,
No, it won’t stop your leak. Your waterproofing is not directly below your tile, it is beneath the mortar beneath your tile. If it is leaking your membrane is compromised. Painting something on top of your tile will not solve the problem.
Water in a traditional shower will get behind your tile in the wall – tile and grout are not waterproof – and make its way down behind the tile, into the mortar bed above the liner, and into the weep holes. If your liner is punctured or otherwise compromised painting Redgard onto the tile on the floor will not help.
You need to find the source of the leak and repair or replace it. Also Redgard will not stand up to direct water pressure meaning the water from the shower head will eventually delaminate the Redgard from the tile surface and negate and effects – if any – it actually had on your leak anyway.
If your shower floor is leaking it should be replaced. I have a handy little free ebook that explains how to do it. I get nothing from telling you that except the distinction of being the ass that tells you what you don’t want to hear.
Sorry.
The chances the water source for your leak are actually coming from water directly in contact with your tile on your shower floor are minimal. It is more likely that the water source is from moisture below the tile. In that case a waterproofing solution on top of your tile will only assist in creating mold and all sorts of nasty things because you are placing a waterproofing layer above a mudbed which has a waterproofing layer below it. We call it a ‘mold sandwich’. Two waterproofing layers with no way to allow moisture to escape only has one outcome and it isn’t good.
Sorry to be the bearer of bad news.
I thank you all for sharing your knowledge. I kind of understood but want to make sure 100% that I got it.
I am redoing my bath and therefore demolished the existing cement board and now I see the studs. Only one of the three sides ( 4th being the entrance in to the shower) has a plastic paper which is covering the insulation. On the other sides (walls) there is no plastic or waterproofing felt.
I am thinking of putting 1/2″ hardibacker board on the studs and apply the redguard. My understanding after reading the above posts is that both redguard and plastic ( or felt) should not be put. SO, I AM THINKING TO REMOVE THE PLASTIC WHICH IS NOW COVERING THE INSULATION. IS THIS RIGHT? Or is the plastic serving someother purpose here? ( I donot understand why they did not put plastic on the other two sides. This is very small shower)
Or ,because plastic is already existing , should I put waterproofing felt on the other two sides and ignore applying redguard? Is this in any way better option than the previous one.
Finally, I will tile the shower surround upto the roof.
Pl help me guys.
Thank you.
Hey skreddy,
The wall the plastic is on is probably a wall on the outside of the house. Regardless you are correct, the plastic or felt should not be installed if you are using Redgard.
You can either use a vapor barrier on the other two walls or you can cut slits into the existing plastic covering the one wall and install your backerboard and use Redgard.
The better option is Redgard since it is a topical waterproofing membrane. The vapor barrier is an acceptable method though if you choose that.
The reason for not having both the plastic and Redgard is that it will form a ‘moisture sandwich’ and not allow any moisture trapped to escape. Simply cutting some slits in the existing barrier will solve this for you. Just one long slit between each stud from top to bottom is enough.
I have hardi backer 1/2 drectly on studs and osb on studs above cast tub and 100% silicone filled seams and edges.
now do I NEED REDGUARD?, spread with trowel before thinset/ ceramic 13″ tile?
and the last 5 inch of hardi backer above the shower heads has allready been finished, textured, painted. tile will overlap this so do I redguard this? and no redguard last 5 inch above tile?
Thank you.
Hi Seans,
You don’t NEED Redgard, but you do need some type of waterproofing membrane because hardibacker is not waterproof. The Redgard can be installed with a trowel if you choose that method. Yes, it goes directly onto the hardi beneath the thinset and tile. Just trowel it on (with the flat side of your trowel) and let it set until it is a deep red. You can then install your tile as usual.
OSB is not a suitable substrate for tile. Two reasons for this are the fact that OSB is actually pieces and parts glued together. Unless it is an EXTERIOR OSB the glue used to do this is not waterproof and will break down if wet. The second reason is that it is wood and will swell and shrink more than a normal wall substrate or backerboard. It should be replaced with hardibacker or a similar backerboard.
Now, with that said, I’m realistic enough to know that I’m not gonna talk you out of it.
So – make damn sure you get good coverage of Redgard on that OSB to ensure that any moisture behind your tile does not reach the wood.
Hi Sid,
You need 1 part Redgard to three parts water. If you choose to do it by the quart it would be 1 quart Redgard to three quarts water.
NEVER use mastic in a shower or tub surround. You can tape the seams with fiberglass mesh tape and thinset and you can also fill the holes with thinset. This will aid in applying the Redgard since you won’t have to fill any holes full of it (it tends to shrink).
Hope that helps.
When you say 1 part redgard to 4 quarts water how much redgard are you talking about. Also, do you put any mastic over the tape on the seams before you apply the redgard. I had someone put up 1/2″ concrete board and 1/4″ fiberboard. I am taking the 1/4″ down do I need to fill the holes with mastic before applying the redgard?
This is a pretty interesting product. Really does go on pepto pink and dries deep red! Here is where I am:
I put the 2 coats of Redgard on last night and did a “primer coat” the night before. This is my first time using this product and I’m not sure if it is thick enough. First I did a heavy coat with a brush in all of the corners. Then coated the rest of the areas with a 3/4 rough texture roller as recommended on the container. This coat seemed to me to be rather thin. I got good full coverage with only a few small spots that did not get covered with the first coat. I then decided to brush on the second coat and applied it pretty heavy. I have a 1 gallon container that is about 1/4 full after the 2 coats and primer coat were applied. The wall areas covered equal about 65 sq. ft. Does that sound right to have 1/4 of the container left or should I apply a third coat?
One thing I should add is I can still read the writing on the Hardibacker if that helps describe the thickness???
If you put both the coats over the primer coat you should be just fine. You can read through it after it dries so being able to read the Hardibacker writing is not really an indication of not being thick enough.
The best thing to do would be a flood test. Plug your drain (make sure you get the plug below the weep holes inside the drain) and mark your water level. Leave it overnight and check the next day to make certain you have not lost water. As long as the level is the same you’re good.
If it makes you feel more comfortable go ahead and put another coat on since you have it left – couldn’t hurt.
Thanks again. I will get working on it tonight!
Thanks Roger. Do you think a 1 g container would be enough to do a 36×42 shower stall? I was planning on going up the wall about 7 ft with it. What do you think?
One gallon should be plenty. Just make sure that you only mix a little of the primer mix at a time. You don’t want to waste a lot of the Redgard for it and have a bunch of primer mix left over that you really can’t use for anything.
Thanks for the advice. I am using hardibacker. What do you think. Does it need that primer coat?
I usually will do a primer coat on hardibacker. It will seal the semi-porous surface and give your first coat of Redgard a solid base to grab onto. If you coat the bare board with a primer solution it will ensure that your two coats adhere fully to the backerboard.
Just read the whole post and answered my own question. Reading thoroughly is helpful! Great posts and fun to read. Keep’em coming
Hi Ian,
Glad I could help!
Depending upon the particular cbu you are using you may want to brush on a primer coat first. Certain cementious backerboards have a tendency to soak in liquid. You can make a primer by mixing 1 part Redgard to 4 parts water. Brush that on to coat the porous cbu then go ahead and roll on your regular two coats.
Just finished studding out a shower surround and installing the fiberglass shower base. Would you use 1 or 2 coats of Redgard over the CBU?
Glad I read this before I put the redgard on. I wanted to do both, but felt uncomfortable that I would be trapping vapor between the two. I already put the plastic up, but can rip it down if you think that the red guard would work better. I am not concerned about the price of the redgard. The shower stall is too small to worry about that.
If it’s a choice between the two I would take down the plastic and use Redgard. Your waterproofing would then be directly beneath your tile which would aid in both evaporation of any water behind it as well as limiting the amount of water able to saturate your backerboards.