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.
Hi Roger,
Your site is the best resource for DIYers I have seen.
I am renovating a small shower. I am ripping out everything and plan to install cement backer board on the walls and a mortar bed. I have several questions. Instead of a slope bed, liner and final bed, can I do a single sloped motar bed and coat with Hydro Ban and if so how do I do the drain? The Hydro Ban site says to use a clamping drain, but what does it clamp to?
Also when I install the backer board to I thinset around the holes for the pipes or do I use sealant?
One final question. In your experience is hydro ban or redgard better, or does it depend mostly on how carefully they are applied?
Thanks again for an excellent site
Hey Terry,
Yes, you can use a single-layer mud deck with a topical membrane such as hydroban. The mud needs to be a minimum of 1 1/4″ at the drain and raise up from there. You have two options for the drain. The easiest would be to purchase a kerdi drain and use it. You can paint the hydroban right on top of the drain.
Your other option is what is known as the ‘divot’ method. This consists of the mud deck dipping down from the 1 1/4″ in the center to the top of the weep holes. It looks like someone left a basketball on top of your drain while the deck mud cured. The hydroban is then painted down into the dip to the top of the drain so the membrane is installed beneath the weep holes. The upper flange then clamps to the lower. You are essentially ‘clamping’ the layer of hydroban. You can read about liquid waterproofing methods on shower floors in this thread: Frankengueuze shower system (the name is just one of gueze’s quirks – he wrote it) The divot method starts on page three.
Thanks Roger for the info on using hydroban.
I am installing the shower in a corner of a concrete block house on slab. 2 walls are furring strips against concrete block and one wall in regular 2×4 studs.
1.Can I install the cement board walls from ceiling to concrete floor and then build the shower pan with a one layer mud bed inside the cement board?
2. Install sloped mortar bed 1 1/4 inch thick at center to 2 inch thick on edge?
3. Install Kerdi drain. Do I seal it in with thinset like in the Kerdi movie or hydroban?
4. Tape and thinset all seams and corners and smooth with thinset or hydroban? Which?
5. Hydro ban all seams and corners. Then hydroban everything with 3 coats minimum?
6. I am concerned with poking holes in hydroban during thinsetting and applying tiles. Does it hurt to apply 4 coats of hydroban to the shower floor? or should I just leave it at 3 and be carefull?
Thanks again for this outstanding resource.
SWEET!!! I love pop-quizzes…
1.Can I install the cement board walls from ceiling to concrete floor and then build the shower pan with a one layer mud bed inside the cement board?
Yes
2. Install sloped mortar bed 1 1/4 inch thick at center to 2 inch thick on edge?
Yes
3. Install Kerdi drain. Do I seal it in with thinset like in the Kerdi movie or hydroban?
Install it with the thinset like the movie then paint the hydroban over the top all the way to the center ring
4. Tape and thinset all seams and corners and smooth with thinset or hydroban? Which?
Both (trick question!) tape and thinset and smooth with thinset THEN hydroban.
5. Hydro ban all seams and corners. Then hydroban everything with 3 coats minimum?
You need to be concerned with the thickness rather than the number of coats. You need about the thickness of a credit card. Normally 3 coats accomplishes this just fine, but make sure the thickness is there.
6. I am concerned with poking holes in hydroban during thinsetting and applying tiles. Does it hurt to apply 4 coats of hydroban to the shower floor? or should I just leave it at 3 and be carefull?
No, it does not hurt to apply more layers. Apply 4 if you want to – and be careful anyway, it’s hydroban – not kevlar.
How’d I do??? Did I pass?
Thanks for putting up with all the dumb questions Roger.
I have been so concerned with how I am going to build the shower that I didn’t pay that close attention to how it is built.
The house is concrete block on slab. Well… the shower bed level, tiles included, seems to be lower than the rest of the floor in the house. The top level of the bed seems to be a fraction of an inch lower than the floor outside the shower and the center drain area is almost an inch lower.
Have you ever heard of this before?
Is it even legal?
Hey Terry,
There are no such things as dumb questions … wait, yes there are, nevermind.
Yours aren’t any of them, though.
Yes, I have heard of that. In fact it used to be common practice to have the slab depressed in areas where tile was to be installed when building a structure. As early 20th century installations were normally over a mud bed, depressing the slab compensated for the thickness of the needed tile substrate – in your case the shower floor. So that is completely normal – and I wish it were still common practice. Yes, it’s legal. As long as your shower floor slopes the required 1/4″ / foot from the perimeter to the drain it’s completely fine. There is no requirement concerning the height of the perimeter of your shower relative to the surrounding substrate thickness – it doesn’t matter if it’s lower or higher. What you have there is an old-school depressed slab for a shower tile installation – and it’s awesome. I wish all my jobs had that.
Well, I finally completed the shower demo. I have a house built in 69 and it seems the older things are the harder they are to take out. Anyway I just got the upper drain flange removed. I am left with a nice smooth cast iron bottom flange and am not looking forward to trying to bust out the floor to replace the trap etc. Since the bottom flange and bolts are in pretty good shape, can I use the new Kerdi adaptor with Kerdi drain??
I watched the video and even though they were putting it on ABS flange it looks like it would work with cast iron. It shows attaching the adaptor with some Kerdi Seal and bolting it snug. Putting in the mud bed around the adaptor and pushing the Kerdi drain flange into the bed. Are these adaptors made to hook a kerdi drain up to all types of bottom flanges?
Thanks again for all your help.
Hey Terry,
Yes, you can use the adapter kit with the cast iron drain. That’s actually the reason the came out with them – we’re tile guys, not concrete guys.
It should bolt right to it.
Hi again Roger ,
I am getting ready to mix up my mud for my shower bed. Its 52 by 32 and will slope just over 1/4 in per foot. The mud calculator said to use 155 pound of sand topping mix and 77 pounds of sand.
I am doing this all myself.
How hard is it for one person to mix up that much mud, allowing time to set the kerdi drain in the adaptor with a small bucket of wetter than normal mud?
Does one person have enough time to do that by themselves?
I will be mixing the mud up on my patio in a wheelbarrow and bringing it into the bathroom with HD buckets.
About how long do I have to do the slope and smooth everything out before the mud starts to set?
Thanks again for all your help
Hey Terry,
One person can do it, I do it all the time! ‘Course I’m likely faster than you’ll be…
Just mix up enough for one or two buckets at a time. You can actually work correctly mixed mud for close to 30-45 minutes or so if needed. Mix up one bucket, install that and see how long it takes you. A lot of times I’ll still only mix one bucket at a time. That’s probably just laziness, though. Once you have the basic shape of your bed you can still work the top of it for up to an hour-and-a-half – two hours or so.
Hi again Roger,
I got the mud bed in today. Found out I had plenty of time to work the mud.
1. There are a couple of spots that are just a little high. I plan on scraping or sanding them down tomorrow morning. Can I do that or should I just leave it alone?
2. How long do I let the bed cure before I apply hydroban?
3. Should I apply thinset over the mud bed before applying hydroban? The mud bed seems sandy and I am wondering if the hydroban would bond better with a skim coat of thinset on the mud??
4. Lastly, Do you recomend fabric or mesh on the mud bed and or seems when doiing a hydroban shower? I kind of worry about just a liquid film on the floor or seems.
Thanks again for your help
Hey Terry,
Yes you can sand or scrape down the high spots. Let the bed cure a minimum of 48 hours before applying your hydroban. You can apply a skim-coat of thinset first if you want to – the hydroban will adhere to either just fine. Fabric or mesh is not required for hydroban, although it doesn’t hurt if it will help you sleep better at night.
My installer put cement backer board up in the shower, but didn’t tape it. It seemed odd to me after the fact, but I went ahead and put redgard on it and did my best to fill all those gaps with gobs of redgard. I have the tile installer coming soon to tile the shower. What should I have him do as far as taping those seems? I think right now he’s just planning on coming in a slapping on some thinset and tiling since I told him I’d put up redgard.
Thanks
Hey Andrew,
The redgard needs to be cut out of that gap and the seams need to be taped and mudded. Redgard can then be installed over the tape and thinset. Taping over it now will do absolutely nothing to lock the sheets together, that gap needs to be filled with thinset and taped.
Sorry, I know that’s not what you wanted to hear.
Hi Roger,
you’ve got an amazing site here. Thanks for helping out the uninitiated (yet brave). Reading your threads has really helped scope this project for me but I have a few unanswered questions.
I’m redoing my bathroom. I’m installing a new tub and intend to tile the surround to the ceiling and replace the old floor tile as well.
I’ve removed the old, avocado tile and the almost 2″ of chicken wire and “concrete” – all the way to the bare studs. Issue number one is is the existing window. It was a retrofit and built in over the old tile. As I chipped away the tile and mud it ocurred to me that I will need to build up the ledges or gasp, get it all out of there and replace the window. Any suggestions on how to build up the ledges and fuse them to the existing tile and base? Material? I do know that I’ll need to be sure the bottom ledge is sloped to ensure water doesn’t settle at the window but I assume the sides and top can be square with the window.
Issue two is mating the cement board to the existing wall. Oddly, the house’s wall are drywall on the studs, a roughly 1/2″ thick cementeous covering, and then paint so it’s not as easy as tape and fading mud. Would you suggest I add new studs to the existing studs but butt them out so the backerboard is level with the old walls or is there something better? You’ve already made me aware of the critical need for Redgard….
If I may, issue three is where the tub meets the wall. I’m installing a drop in cast iron tub. It has a downward sloping, flat bottomed lip – approximately 4″ all the way around. I intend to simply install 2×4 braces around the tub to ensure it doesn’t rock. Do I need to have an exposed ledge (tiled) to make the transition between the tub and wall? Spece is absolutly minimal so I would like to avoid the ledge. But I’m concerned about the sloping lip meeting the wall tile.
Thanks again for your help!
Marty
Hey Marty,
the easiest way to deal with that window would be to add a new frame around the perimeter of it then screw backerboard to the new framing to whatever depth you need. There are several different types of windows and the way they were dealt with but that is essentially the basis of retro-fitting one for tile. yes, the remaining three sides can be square with the window.
If your current studs are plumb you can just add additional furring strips in front of them to the depth you need. If they are out of whack you can add new studs to the existing, it’s called sistering the studs and we do it all the time.
Whatever will work best to be both solid and the correct depth.
The drop-in tubs are not supposed to be used in a shower application. Lecture over.
The best way to work with that is to install the tub directly against the studs so that the backerboard sits above the horizontal arm. You didn’t say whether the lip sloped toward or away from the tub. If toward that should work fine. If it slopes away you will need to figure out some way to pitch that lip into the tub. Otherwise you will have sitting water just trying to get back into your wall. A tiled ledge above that arm, perhaps? The slope cannot slope toward the wall, though, that will create all sorts of problems.
Hi –
If I need to install a ledger board to tile the shower, what’s the best way to seal the holes in the RedGuard and durarock after I remove the ledger?
Thanks!
Hey Bob,
You can use 100% silicone or you can go over it again with redgard (a couple of times) until it seals them up. Either one will work fine – the silicone is much faster.
Please don’t hate me, but I am taking the easy way out for our tub surround, and tiling right on our blue board. Underneath the blue drywall is a layer of plastic on the back wall (protecting the insulation on the outside facing wall), but not on the other two (the wall with the shower head and the opposite one). I was wondering if I should put Redgard on any of the walls, or just make sure that I seal the grout very well. This is not a job that is expected to last a lifetime, or I would be using concrete backer board, but how do you suggest I make it last the longest with the scenario I have laid out.
Thanks,
Aaron
Why would I hate you, it isn’t my shower, or one I’m responsible for. Build it out of paper mache if you wanna.
Two things you should do for that incorrectly-built shower – coat the hell out of every wall inside of it, even the one with plastic. If you’re feeding mold it doesn’t matter if plastic is there or not. And make sure your homeowner’s insurance is up-to-date.
‘Sealing the grout very well’ will do absolutely nothing to prevent moisture from getting behind your tile. Sealer does not waterproof, it stain-proofs. (actually stain-resistance, but that’s simply a semantic difference in your situation) Oh, and keep a fire extinguisher next to your dog.
I guess I could’ve just read your response to Bruce, sounds like his is a pretty similar situation to mine. Thanks for the advice, I’ll keep an eye on my dog.
Bonjour Roger deMontreal Canada,
I am in the process of redoing a bathroom, tiling around the bathtub.I used a cement backerboard and megalite with a mesh to close the seams around the tub.Given I did not use a vapor barrier on the exterior wall reading from prior posts I believe it is not ecommended. People at H.D. made me aware of Redgard yesterday.Is it easy to use and how to apply it? would a paint roller do. and which kind to use. How long does it take to dry, would one coat be sufficient.Once it dries then I would use the mortar than apply the mosaics.No one at HD had the time to help me. I am a first -time DIY.
Regards.
Bonjour Jacques!
Redgard is very easy to use. You can use a paint roller with the thick nap roller on it. You will likely still need two layers, however. The finished thickness should be the thickness of a credit card. Use a paint brush to do your corners then roll the rest on. Once it cures to a dark red (couple of hours) do it one more time. Give that a full day to cure and install your mosaics with regular thinset mortar right to the redgard. Very easy stuff to use, you should be fine with it.
Hi,
My project is a bathroom renovation, specifically a shower floor. I’ve built up the shower floor as per your instructions on the site and am at the final stage before tiling. I was planning on using redguard as final prep to the entire shower surface (added insurance) before installing tile. I like the ease and application of ceramic tile adhesives for installing tiles on walls (never on floors), particularly OMNI Grip made by CBP, the same company of course as red guard. The product packaging does not recommend using a tile adhesive over redguard. Have you had any experience with this? What do you recommend?
Thanks in advance!
Hey Trevor,
Do not put a layer of redgard over your shower floor as a precaution. It will create two waterproof layers (membrane and redgard) with deck mud trapped between them. You’ll create a host of problems with your shower. Ceramic tile adhesives (mastic) also do not belong in wet areas such as showers. If you read that bucket it should also state it is not recommended for tiles over either 4 or 8 inches square – that’s because it will rarely fully cure when placed beneath a large tile – it requires air to cure. If you place it over redgard you are trapping it between two essentially air-proof products – it’s never going to cure. I recommend just regular thinset. It’ll hold your tile just fine and fully cure easily enough.
Provided you followed those instructions with your pan you don’t need any added insurance. They’ve been built like that well over 75 years and they last. Really.
Just redgard your walls and use thinset.
Hi Roger
I need your input. I plan to tile around a cast iron tub. The tub has a lip. I first installed building paper(felt, tar paper depending where you’re from) almost like origami,straight folds, pristine cuts around plumbing and caulked with Henry’s roofing emulsion around cutouts and on staples. The paper folds out over the tub lip and extends to 5 ” from the ceiling as we had intended for tile to run up to 60″ from top of tub. I then installed Hardiebacker and held it about 1/4 inch off the lip to prevent water wicking (would that be wiki leaks?) figuring I would drop the tile down to within 1/8 ” of tub and then caulk. The valve mixer started leaking and then design changes including raising the shower head so water would not land on the chest of the average guy. Fast forward to me removing the backer board and getting different mixer.The tile is now going all the way to ceiling and along one entire wall. Now I am planning to reinstall backer board and I notice the tarpaper is perforated with all these holes from where the screws were. I am re-purposing the used board to go all the way to ceiling and along one entire wall so these pieces will have errant screwholes in them as well.
I was planning on using redgard on the backer board because I worry that now the paper is perforated I have lost my moisture barrier. Theoretically if moisture found its was through the grout,along a screw it would not penetrate to the framing but run down the face of the tarpaper out over the lip and back to the tub via a weep hole. But now that I have essentially a tarpaper doily wouldn’t I be better off coating the screwholes and the thinset taped seams and inside corners at least? Is it either or? Either redo the tarpaper entirely, or Henry’s tar mastic over the holes in tarpaper, or leave the holes in tarpaper and coat the entire face of the backer board with redgard? Or just coat the seams and extra screw holes in the re-purposed pieces? I know I’m overthinking this but I want this installation to last. One last question. If this emulsion is moisture proof how the heck could water get past it and then behind the backer board to linger and fester? What to do? Someone has to stop me before I hurt myself by wringing my hands this much. Would appreciate your wisdom. Thanks
Hi Delia,
I would either replace the paper with new or coat the old screw holes with the tar mastic. Simply coating the seams and corners on the hardi will not prevent moisture from getting back to the paper. It will go through the board – the entire board, not just where the screws are. Hardiebacker is not waterproof, it’ll soak in moisture. Water will get to your building paper. The best thing to do would be to simply replace the paper with new stuff. A couple of hours worth of work now will ensure a water-tight shower.
When you say ’emulsion’ I assume you mean the tar mastic? As I stated, hardi is not waterproof. It is water stable – it won’t disintegrate or fall apart when it’s wet, but it will soak in moisture. It’s completely normal. Unless you coat the entire board with the product water will get behind your backerboard.
Hi Roger,
Thanks for your “Shower Niche” procedures. I have started the process but am somewhat confused regarding the poly/redguard conversations, specifically on an exterior wall. I have Durock on all three of the shower walls above the tub. The two interior walls in the shower do not have poly or insulation, and I was going to use Redguard on all of the walls. The third wall, however is an outside wall (including window). On this wall I have insulation, poly, and then my Durock. is this wrong? Code here (Canada) states I require vapour barrier on this external wall. Please help!! I want to get this job overwith so I can start on the next bathroom. Any input would be greatly appreciated.
Hey Bruce.
Canadians, shoulda known.
Just kidding. I believe (although I’m not 100% positive about your codes) that the house wrap constitutes a barrier on that outside wall. Like I said, not positive. In any case it would be best to slice or cut slits into the poly over the studs so moisture doesn’t get trapped between that and the redgard. If, however, that nullifies your compliance with the building codes you obviously should not do that.
I’m a lotta help, huh?
O.K., what is worst case scenerio with the wall should I chose not to take the wallboard down and slit the poly? I will most likely do it, but just curious. Oh, sorry, I forgot to add Ehh at the end of my sentence like us Canadians all do.. Kidding.
Thanks Roger.
Hey Bruce,
Any moisture that is trapped in there will have no way to dissipate. If it just sits between those two barriers it may begin to feed mold spores. Mold doesn’t quit – it’ll continue to grow and eventually compromise your shower, structure, sanity and your dog may burst into flames. You always want a way for moisture or vapor to dissipate. Whether that is simple evaporation or down into the drain you want to be able to channel that moisture where you want it. You never want it to simply sit there and look for ways to wreak havoc.
Hi Roger,
We have the hardie backer up in our tub/shower and were preparing to Redguard when I realized that I didn’t know what to do with that gap between the tub. I see in your answers here that we should run silicone around the gap to fill it. However, I’m getting confused about leaving the weep holes that you’ve mentioned in other posts. Should there be NO gaps left in between the hardie backer and the tub? And the weep holes are just placed in the final silicone bead between the tile and the tub? Or should we leave a 1″ weep hole between the backer board and the tub? I’m guessing there should be no gaps between the backer board and tub, but just want to be sure we are doing this right.
Thanks
That is correct – no gaps between the backer and tub. Your weep holes are only installed into the bead of silicone around the tile itself. Moisture getting behind the tile will hit the redgard, run down and out those weep holes. If you have gaps in the silicone bead between the backer and tub the water can run into your wall – don’t do that.
Mornin’ Rog’!
No clever opening today. It’s Sunday &, quite frankly, I’m burned out from searching for a particular cure for my shower prepping journey. We’ll be using cement board w/hydroban for the walls. Wasn’t planning on tiling the top 8″ or so. (just because that’s where the old surround ended. If I chose to leave that 8″ for painting, how do I prep it? Cement to the ceiling or switch to green board? Or, since the space to the ceiling is so minimal, should I just tile all the way up??
Burnt in NY,
Lori
Hey Lori,
I always run the cement board to the ceiling. You can coat it and prime it for paint just like regular drywall. When possible I like to run the tile to the ceiling as well, I just think it looks better. That, however, is merely a personal choice. You can paint over primed backerboard if you need to.
In the process of redoing the entire bathroom, insulated and put up a poly vapor barrier on all walls, then put up cement board for the shower, walls and ceiling. Was planning on using Redgard but it sounds like this is a no no from reading previous comments and I’m not sure I want to take all the cement board off in order to take the poly off! If I just leave the walls as is and then apply my thinset and tile will I be as protected for water damage, leakage, etc. Is Redgard an absolute necessity or an added preventiitive measure.
Hey Rob,
As long as your barrier laps over the flange of your tub or base so moisture can run down into the drain rather than into the wall then you’re just fine. Redgard is one particular method of waterproofing a shower, as is a barrier behind backerboard. They are two different methods of accomplishing the same thing.
Great site and advice. We are remodeling the Master Bath. The tile contractor is going to use RedGard over 3/8″ Hardibacker for the shower. Two walls of the shower are exterior walls. The exterior wall insulation paper face was not sliced (I just read that may be a concern). We live in the north Atlanta, GA area.
The tile and 3/8″ backer board will go to approximately 7′-2″ A.F.F. with 1/2″ green gypsum board for the highest two feet (note the offset in thickness). The contractor has used regular drywall joint compound to level the joint between backer board and green board. He has used green mold resistant fiber mesh tape at all joints. He is going to simply RedGard over the mesh tape (no bedding of tape at hardibacker joints) and the drywall joint compound joints before thin setting the tile. I think he anticipates only one coat of RedGard but some joints are as much as 1/4″ to maybe 5/16″ gap in the corners. Also, he is going to RedGard the floor concrete slab then install the sloping thick pan then another coat of RedGard over the pan before he starts tile. Does this create a double moisture barrier problem? Currently the floor drain is about 1/4″ above the concrete slab (before the pan is installed).
How does this all sound? Do you see any problems? Can address them all for me?
Hey John,
Paper face on insulation is not as dire a problem as a plastic barrier would be. It should be sliced, but it isn’t imperative, that alone should not cause problems.
Greenboard is NOT an approved substrate for a wall, tiled or not, inside a shower.
One layer of redgard is rarely sufficient to get the required thickness, it can be done, but it would need to go on very thick to achieve that.
Regular drywall compound is never a good idea, but it can be done up that high (higher than the shower head) in a standard shower provided it was the powdered type mixed with water and not the pre-mixed stuff – it re-emulsifies when exposed to moisture.
Not sure what ‘green mold resistant fiber mesh’ is – never seen it. What you need to be concerned with as far as the mesh tape is alkali resistance. Thinsets contain alkaline which will break down regular mesh tape or tape not made to handle them. Dunno if the green stuff is or not?
The seams and corners NEED to be taped and mudded with thinset – this solidifies the installation and creates one large monolithic structure. If they are not mudded each board may move independently of the adjacent boards and may lead to cracking tile or grout. There is no way in hell, no matter how thick he applies the redgard, that he is going to get those filled and not have it shrink back – it just won’t happen.
Redgard on the concrete, deck mud, then another layer of redgard IS NOT an approved method, nor is it a viable one. The weep holes in the drain need to be accounted for when using a topical membrane with a three-piece clamping drain. Not only does that create a moisture or mold sandwich, it leaves access for moisture to get below your waterproofing through the weep holes. The concrete may be redgarded in this scenario, but 1/4″ of stagnant water laying on a flat, dark floor with no way to drain nor dissipate…well, you get the idea. That is not correct or acceptable by any standard at all.
I put plastic sheet in as a vapor barrier but had to cut it in several spots to fix my mistakes. I know that it isn’t adequate as a vapor barrier and want to use Redgard. Will I have problems if I have Redgard and plastic if I did a crappy job on the plastic?
Hey Steve,
I honestly don’t know. How badly did you massacre the plastic?
If it were me I would likely remove the plastic and reinstall the backer. If you have one area between two studs where the plastic is intact that is essentially a column of two waterproof barriers with backer sandwiched between them – moisture cannot dissipate, not between those studs anyway. I think I would sleep better at night if I removed that barrier behind the backer before using redgard. You may or may not have problems with it.
I’m a lot of help, huh?
What to do if installer coated FLOOR with hydro ban? They did walls too but I’m concerened about the floor…it’s a standard shower/ not a steam shower. Thanks
Hey Brantley,
Let the installer continue to do his job.
Hydroban is a very good product rated for shower floors (submerged application) as well as walls. It is a standard installation practice. And it’s good stuff, so it sounds like he knows what he’s working with – people that don’t do not buy the expensive stuff. 
Oh, have another question on this subject too. While I would love to tile my shower all the way up the wall and over the ceiling, I’ve decided I don’t want the hassle of doing the ceiling. We had a bulkhead for some reason over our shower that we ripped out, and we used hardie-backer on the ceiling. Since I won’t be tiling it, I’m not sure what is appropriate to put on top of the hardie because it’s rough and the screws leave those rough edges when drilled down. We are using Redguard for our waterproofing. Can we redguard first, then cover the ceiling and 8″ of the upper walls with drywall cement to get a smooth surface for painting? Or if we use some type of filler over the screws and sand down the rough edges, will the redguard make the surface smooth enough to paint right over it? I don’t want to mess up the top after we will have spent so much time tiling.
Unless you have an enclosed shower (dropped header on top and sealed) or a steam shower there really is no need to waterproof the ceiling, although you can if you want. Get a drywall sanding sponge and that’ll knock off those edges right off. The redgard will leave it smooth enough to paint. You can use drywall mud but be sure to use the powder you mix with water and not the pre-mixed stuff – it’ll disintegrate. You can simply skim over the hardi and paint it as normal.
Hi,
I was reading your article on Ditra and one of the questions was regarding laying slate on a patio. Your advice was to not paint the flooring base (plywood or concrete) with a waterproofing compound like Hydroban as mortar will not be able to grab properly onto/into the plywood/concrete. This makes sense, but as I understand one can paint the floor in a shower or other small wet areas which will be tiled. Is this because such a small area is considered “low traffic” and has a low risk of the bond detaching from the Hydroban paint? Thanks.
Hey Paul,
You’ll need to be a bit more specific about the particular comment for a complete explanation, I don’t actually remember all 2700 of them.
If the question was regarding painting the waterproofing liquid onto the substrate before installing ditra then I advise against that due to the fact that you would be thinsetting a waterproof membrane to another waterproof membrane – no real need for that and you may end up trapping moisture between the two with no way to dissipate. Thinset sticks just fine to hydroban whether it’s a large area or a small one – there must have been other factors at play for me to advise that – or, you know, I may have been drinking.
Michael-
Great article. A question on taping seams- the instructions say that redgard is ok to use on gaps 1/8″ or less- do I still need to tape?
Hey Greg,
You don’t need tape but it will make your job easier and use a lot less redgard. Redgard shrinks as it cures so you would need to put four or five coats to get that gap filled. Also, regardless of how big the gap is in the seams you still need to tape and mud them with thinset – always. Makes no difference whether you are using a vapor barrier or redgard. This is to tie them together and control movement – it has nothing to do with waterproofing.
I’d like to retile our shower. It currently is backed with regular drywall. Redgard seems like a good product to use over the existing drywall, then retile. What problems would you see with that?
Hi Michael,
Redgard is not approved for drywall. You need to replace the drywall with cement backerboard or other suitable substrate. Drywall is only an acceptable substrate for shower tile if used with a sheet membrane such as kerdi.
Roger, will I need to use a special thinset for Red Gard, or will Versabond work? Also, since I’ll be using Red Gard, do I need to put either fiberglass tape or silicon caulk on all joints, corners and along top and bottom? Thanks.
Hi Richard,
No special thinset needed – versabond will work just fine.
You need to tape and mud the seams and corners with alkali-resistant mesh tape and thinset. Let that cure then install your redgard. If you need to paint some of those areas where they go into non-tiled areas you can simply paint right over the cured thinset.
I am in the process of rebuilding a shower. I put in plastic on the ceiling between the insulation and under the cement board (no vapor barrier on that insulation). I had planned on doing the same to the outside wall over the insulation, I was going to score the backing on the insulation first before covering it. After reading your post, I feel that I should take the ceiling down and remove the plastic. Is that the correct thing to do? In the end my entire shower enclosure will be cement board then tiled. We had a bad experience with mold from the original builder. Don’t want that ever again. Thanks
Hey Bob,
If you are using redgard on your backerboard then yes, remove the plastic. You need one or the other – never both.
Thanks for the advice, looks like the wife will have to take the ceiling down now.
USED RED GUARD ON THE CEMENT BOARD IN THE SHOWER AREA. WILL BE INSTALLING TILE OVER THE RED GUARD IN A FEW DAYS. IS IT OKAY TO USE THE SHOWER BEFORE TILES ARE INSTALLED ??
Hey Michael,
Nope. The shower is waterproof but the pressure from the shower head may compromise the membrane. Think about placing rubber cement on a window and trying to spray it off with a hose – same thing.
I used a plastic vapor barrier behind Hardeeboard. I will be using RedGuard on the seam tape and screw surfaces only and then ceramic tiles. Am I going to have a problem with mold if I don’t coat the entire face of the cement board with RedGuard?
Hey Joe,
Nope, no problems at all. No real reason to do that, though. The vapor barrier is your waterproofing and the redgard is overkill that really serves no purpose. However, if it makes you sleep better at night that right there is reason enough, eh?
It won’t hurt anything.
Hi,
Were are redoing our bathroom and doing a tub with a tile surround. One of the walls is an exterior wall and we have faced insulation on that wall. We are using cement board on the floor and the tile surround. We will be using red gard on the tile cement board, so from what I am reading we would not use the poly vapor barrier? And the insulation would need to have slices to beathe?
We are using green board for the rest of the bathroom, what kind of insulation should go in the interior walls- and do they need to have poly there?
Thanks in advance for the help!!
Hi Bridget,
That’s correct – you need to slice the face of the insulation when using redgard.
Insulation is not required at all on interior walls, but you can always use it if you want. Just regular rolled batting will be fine. Walls in your bathroom, not in your shower, do not require a moisture barrier since they are not considered a wet area.
Sir,
I’ve been reading all the comments left here, and I’m not going to ask about the double moisture barrier. (I think I got it) I have the plastic behind the cement board, so i WILL NOT put redgard over everything. My concern is that in all these comments, it seems as if vapor penetration is inevitable. Is this true or is this just a worse case scenario assumption? The comments make it sound as if water is going to go behind the tile wether I like it or not. Isn’t the tile supposed to stop the water?
Hi Dustin,
It is a common misconception that tile and grout are waterproof – they are not. Every tile has what is called an ‘absorption rate’, this is a measure of how much water that particular tile absorbs when subjected to water – all tiles will absorb water. If this absorption rate is less than 0.5% it can be classified as a porcelain tile. Even with that you have 5/10’s of 1% that define the amount of water that porcelain will absorb – the less the better, but it will take in water. Thus water will get behind your tile.
Regular cementious grout absorbs water just like regular cement – it’s a cement-based product. Think about your driveway when it rains – it turns dark. It does that because it soaks in water. As the water dissipates either through evaporation or draining into the ground beneath the slab it will lighten back up. Your grout is the same way – it’s porous.
The only thing you can do is control the water and eliminate conditions in which mold and mildew and the like thrive – hence not using a double barrier. The method you choose to waterproof your shower – whichever membrane or barrier that may be – is what stops the water. You can take every precaution to lower the amount of water getting behind your tile, but it’s nearly impossible to eliminate it. The best method is to use a porcelain tile with the lowest absorption rate and use epoxy grout. This will eliminate nearly all the water behind your tile. There are tiles on the market known as ‘impervious’ tile like glass which does not absorb water, but it’s normally very expensive to tile an entire shower with it.