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RedGard Waterproofing for Cement Board Shower Walls

RedGard waterproofing is an affordable way to waterproof shower walls.

But the problem is that many people use it the wrong way.

And sadly, that can cause mold and mildew problems inside shower walls.

In this tutorial, you’ll see how to use RedGard waterproofing on cement board shower walls. I’ve got a lot of invaluable tips that hopefully help you out.

Let’s dive in!

RedGard Waterproofing Questions

Is RedGard a good waterproofing?

Yes, RedGard waterproofing can waterproof cement boards (DuRock, Permabase, Hardiebacker). It’s a liquid membrane applied to substrates with a paint roller. Thus, it’s easy to apply. However, RedGard should not be used over drywall in shower areas per the technical data sheet.

RedGard Waterproofing

Can I tile directly over RedGard?

Yes, RedGard can be tiled over inside showers and on floors. RedGard has to fully cure before being tiled over. A polymer-modified thin-set that meets or exceeds ANSI A118.4 or A118.15 should be used to set tiles. Every thin-set mortar will have these ANSI ratings printed on the bag.

How many coats of RedGard should I apply?

For general waterproofing, RedGard waterproofing should be applied at a rate of 110 square feet per gallon in each coat. A minimum of two coats is required when using a brush or roller. The second coat should be applied at right angles to the first coat. A minimum 15 mils thickness is recommended above a tub surround or shower floor cove. Use a wet film gauge to measure the 15 mil thickness.

Is RedGard required for shower walls?

Liquid membranes like RedGard are recommended by the Tile Council of North America for cement backer board walls. However, if foam backer boards like KERDI-BOARD are used, then RedGard is not required. Liquid membranes like RedGard waterproof cement board walls and slow the rate of vapor transfer into stud cavities.

Cement Board Tips for RedGard

The last few posts about this bathroom remodeling project discussed hanging cement boards and how to work with Permabase inside showers.

Cement board is the cheapest backer board for showers.

I also like KERDI-BOARD because it’s faster to install. Whether you’re doing a small bathroom remodel or a large project, the tips in this tutorial are great.

Adding self-adhesive alkali-resistant fiberglass tape to all the cement board seams is a really important step.

This tape needs to be applied to every area where the cement board panels butt against each other or other sections of drywall/plaster.

I added tape to all the seams and then used a thin layer of polymer modified thin-set to embed it onto the cement board.

The mortar consistency should allow it to just barely hang off a margin trowel or putty knife.

Smooth out the thin-set before it dries. Use a damp sponge to feather the thin-set because any ridges or bumps will cause the tile to lay unevenly.

Use a level to check and fix any peaks or valleys.

I also applied a thin layer of thin-set to all the screw heads in the cement board.

By the time you’re done with doing all this, your bathtub space will look like the following picture.

The thin-set will need to dry for about a day.

This is especially important if you’re installing subway tile showers.

The smaller the tile the flatter the backer board has to be.

Otherwise, the tile will be wonky and look super unprofessional.

Prep Work for RedGard Waterproofing

The prep work for RedGard waterproofing is straightforward.

Since it does have a thick texture, RedGard should be applied only to the areas where there will be tile.

Also, don’t get RedGard on the tub.

I used blue tape along the edge of the tub where it met up with a cement board.

Then, I placed a piece of cardboard on top of the tub to further protect it from any RedGard drips.

The last step for RedGard prep is to dampen the area where it will be applied lightly.

This is especially important for porous substrates like cement board.

I used a bucket of water and a sponge.

Take special care to get the corners of the cement board damp as this is the location where you want the RedGard to adhere.

Lightly Dampen Porous Substrates Prior to RedGard Waterproofing

Now the RedGard is ready to be applied.

And this is where a lot of folks make mistakes.

RedGard Creates a Waterproof and Crack Resistant Membrane

Applying RedGard to any surface is super easy.

If you can paint a wall you can use RedGard. And for this shower, we only needed one gallon.

RedGard Waterproofing

There are two ways to get RedGard on cement board panels:

  1. Roll it on the wall with a 3/4-inch nap roller
  2. Trowel it on the wall

Use a good roller that won’t shed into the RedGard.

I like Purdy rollers and used a 3/4″ nap roller for this project.

How to Apply RedGard Waterproofing

The first application was put on vertically.

Waterproofing with RedGard

Use a paintbrush for areas that are unreachable with the roller.

I pay close attention to applying a good coat of RedGard to all the corners and spaces adjacent to the tub since these are the areas that water likes to penetrate the most.

RedGard Membrane

How long does it take for RedGard membrane to dry?

I let this first coat of RedGard dry until the panels appear red. This took about 1 to 1.5 hours.

Drying time depends mostly on temperature & humidity.

And the surface will appear pink until the RedGard has completely dried.

How many coats of RedGard

When the RedGard appeared red and wasn’t tacky I applied a second coat horizontal to the first.

Again, as you roll it on the walls, check to ensure there are no bumps or small lint boogers in the coating.

The end result should be a bathtub surround that is red in color.

RedGard Waterproofing on cement board

The bathtub walls are now completely waterproof and the RedGard also serves as a crack isolation membrane.

This means RedGard will expand and contract ever so slightly to prevent cracks from forming in the shower tile.

Keep in mind, that the thickness of RedGard should factor into how far to set a shower valve like the Delta R10000.

What’s Next

One of the biggest problems with bathroom remodeling is piecing together all the different parts.

Understanding the nuances of waterproofing, tile work, and plumbing can be confusing.

And that’s why I created our Home Repair Tutor Platinum Membership.

It explains all these puzzle pieces in detailed step-by-step tutorials.

I promise it’ll make your project easier and give you the results you want.

Tap the button below to learn more



RedGard Waterproofing