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.