***RedGard is not paint.***
It does not waterproof by color, coverage, or the number of coats you apply. RedGard only works when it is applied at the manufacturer’s required thickness, over a proper substrate, with reinforcement at seams and changes of plane. A red wall does not mean a waterproof wall.

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. 

Your cement backerboard must be installed correctly WITHOUT A VAPOR BARRIER BEHIND IT! You do not want an additional barrier behind your backerboard if you are installing a topical waterproofing membrane over the front of it.

You HAVE to tape and mud the seams and any changes of plane (corners) as described in the post I linked to above. Just applying the fiberglass tape with Redgard over it is not sufficient. You need to install the fiberglass tape on all your seams and corners with thinset, let that cure, then paint the membrane over it.

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 consistency 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.

First, let’s talk about the REQUIRED minimum thickness for these products in order to guarantee that they actually waterproof your shower. Every manufacturer has a required thickness for their product.
Redgard’s required cured thickness is 30-35 mils (walls) and 60 mils (floors).
A mil is one-thousandth of an inch, which makes as much sense as every other Imperial measurement.
Hydroban’s required minimum thickness is 15-22 mils for walls and 22-30 mils for shower floors.
But I’m not gonna make you whip out a micrometer.
A standard credit card is 30 mils.
See how easy that was?

So let’s make it harder: these membranes shrink as they cure. By about half. So a 30 mil cured layer will need to go on at 60 mils – double.
These products also recommend two coats.
Only two coats. (more, thinner layers IS NOT better). So when you begin coating your substrate you want to put it on at about the thickness of a credit card. It will dry and shrink to about half, then install another layer at the thickness of a credit card, which will then dry and shrink by about half.
When you’re finished you’ll have two layers at the correct cured thickness (~30 mils).

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 lieu 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. Note that the required minimum thickness for the membrane on a shower floor is different than required on the walls. It’s normally double (but again, every product is different).

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.

RedGard website

Laticrete website

 

 

Common Mistakes and Fixes

Applying RedGard too thin

Each manufacturer has their own required thickness to guarantee the product will waterproof your substrate correctly – READ THEM. Seriously. The minimum thicknesses for Redgard and Hydroban are listed in the post above. If you use one of those – check them anyway. Products change, sometimes the installation procedures change with them. Ensure that you check the requirements for whichever product you choose.

Skipping reinforcement at changes of plane and seams

You must first ensure that your backerboard is installed correctly. That includes alkali-resistant mesh tape and thinset at all changes of plane (corners) as well as all seams. This reinforcement is necessary. Start with properly installing your substrates. Redgard alone is not sufficient to bridge gaps.

Installing RedGard over an improper or unprepared substrate

Drywall IS NOT an acceptable substrate for liquid waterproofing. You must use cement backerboard (or fiberboard). Before you install the membrane you must either prime it (with a watered-down coat of the membrane) or sponge it down to remove all the dust, and ensure it’s what’s called SSD – Saturated, surface dry. This is to make sure the backerboard does not prematurely suck moisture out of the membrane. Just sponge it down really well, then when the surface is dry you can install your membrane.

Frequently Asked Questions

How thick does RedGard need to be to be waterproof?

Redgard’s required cured thickness is 30-35 mils (walls) and 60 mils (floors). Redgard shrinks about 50% from the wet thickness to the cured thickness. It needs to be put on in two coats. Two coats only, more, thinner layers is not better.
A regular credit card is 30 mils thick.
So: Install your first coat the thickness of a credit card. When dry, it will be about half as thick. Apply your second coat at the thickness of a credit card, once cured your entire installation will be the proper thickness of a credit card.
Each product has it’s own required cured thickness. Check your particular product for their requirements.

Do I need mesh tape or fabric with RedGard?

Yes. But the mesh tape with redgard over it is not sufficient. You need to install the tape and embed it in thinset while you are prepping the backerboard installation. You do that just like you would with drywall.

How long do I wait before applying the second coat or tiling over RedGard?

Redgard (specifically) is ready for the second coat in 1-1.5 hours. You can start the second coat once the first turns to a dark red and is no longer tacky to the touch. You can begin installing tile over it once it is cured (not dry – cured). That takes 12-24 hours. Humidity, temperature, and other factors come into play to determine the amount of time, but a full 24 hour cure will ensure it’s ready to tile.
As with all these products, each manufacturer has their own specifications, be sure to check your product for the answer.

Can I use RedGard over cement board / drywall / existing tile / mud walls?

Yes, you can use it over cement board. No, you cannot use it over drywall, You MAY be able to use it over existing tile. Yes, you can use it over mud walls. As a general rule it can usually be used over any water-stable substrate (that is any substrate that does not degrade or change dimensionally – swell, warp, etc., when exposed to water) . The issue with drywall is not that it won’t make the surface wateproof, it will. But moisture, vapor, etc. can get into the substrate from behind it as well. If your substrate degrades it doesn’t really matter whether the paper on the front is waterproof.
The biggest two issues with going over existing tile is the stability of the installation and whether the redgard will properly bond to it.

Related Posts

Installing cement backerboard for your shower walls
Shower tile basics
The divot method

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.