Waterproofing Drywall For Shower: 3 Step Definitive Guide

Whether you’re remodeling your bathroom or building a new one from scratch, the first thing to do before tiling your shower is to waterproof the drywall behind the tile. This step is crucial to prevent wall damage and mold problems. 

Waterproofing drywall for the shower requires you to coat the surface with a waterproof membrane. Elastomeric waterproofing materials are generally the best choice. Alternatively, you could use oil, shellac, or water-based polyurethane primer for drywall, although the shower’s lifespan will be shortened. Installing waterproof drywall or cement boards are other alternatives.

Also See: Drywalling a Bathroom in 6 Easy Steps

How To Waterproof Drywall For Shower

The only right way to waterproof drywall for showers is with a building membrane that creates an effective barrier against moisture. Alternatively, you can paint the surface with a waterproof primer. Regardless of the product you use, follow the quick steps below.

Things You Will Need

  • Drywall sealant 
  • Caulking gun
  • Putty knife
  • Sandpaper 
  • Waterproofing membrane or waterproof primer 
  • Paintbrush
  • Rubber gloves 
  • Respirator 

1. Choose the right drywall for your shower

The first step when building or restructuring a shower is choosing the right materials. There are several types of drywall, but not all are suitable to use in humid environments, such as the bathroom or kitchen. 

For your shower – and the rest of your bathroom, as a matter of fact – you should use mold-resistant drywall (blue in color). This choice can prolong your shower’s lifespan by preventing the growth of mold if the moisture somehow manages to pass through the tile and waterproofing coat. 

Without waterproofing, regular drywall resists up to ten years in a shower. Comparatively, you can expect mold-resistant drywall to last 20 years or more.

2. Seal the joints and cracks

After you’ve installed the drywall panels, sealing the joints and eventual cracks is a crucial step before waterproofing its surface. Otherwise, moisture could still get through and soak the panels, causing resistance problems as well as mold and mildew if you haven’t used mold-resistant drywall.

Drywall sealant is similar to caulk and comes in tubes that you can use with a caulking gun. Apply a thin layer of the product along the joint, then spread it with your finger (covered in a rubber or latex glove) to push the sealant inside the joint. Reapply if necessary.

To seal the cracks, apply a small quantity of sealant over the crack and spread it over the damaged area with a putty knife.

Let the sealant dry and cure for 15-20 minutes before proceeding

If you’ve sealed any cracks, you may have to smoothen the surface with sandpaper before applying the waterproofing coat.

3. Waterproof the drywall

Once the sealant has cured, you can proceed to waterproof the drywall. As explained above, you should use a waterproofing membrane for drywall

This product generally costs more than waterproof primer, but once cured, it acts as a strong barrier between the drywall and tile or paint topcoat. Alternatively, you could use a high-quality waterproof primer, preferably oil- or shellac-based.

Unlike wall paint, the waterproofing coat must be applied to start from the joints and then move to the center of the panel. 

Apply the product with a paintbrush in a uniform layer along all joints. You can then continue applying the waterproofing membrane or primer on the rest of the panel in a thin layer.

Let the first coat dry as instructed on the package (time could vary from four to 16 hours, depending on the product), then apply a second coat following the same application pattern.

Let the second waterproofing coat dry and cure for at least 24 hours before tiling or painting the wall

Throughout the process, maintain the room well ventilated to prevent the accumulation of toxic fumes and to speed up the drying process.

Related: How long should you wait for the grout to dry before showering?

Other Waterproofing Alternatives

Waterproofing the shower drywall with a waterproofing membrane or a waterproof primer is the best choice. However, you can also use one of the alternatives below.

RedGard Over Drywall

RedGard is a liquid-applied elastomeric waterproofing membrane similar to the drywall waterproofing membranes. It complies with the Uniform Plumbing Code and International Plumbing Code for use as a shower pan liner, and it can also be used to waterproof the drywall in your shower.

The product has a thick consistency and is slightly harder to apply compared to a primer, but the result is longer lasting.

RedGard is an excellent alternative to drywall waterproofing membrane if you haven’t found it in your local home improvement store.

Cement Board Instead of Drywall

Cement board is a common replacement for drywall in showers. Its main advantage is its long lifespan. Even if soaked with water, the cement board will not rot and will provide a solid backing for your shower tile. 

However, you should know that the cement board is not water-resistant (nor does it come waterproofed). While moisture won’t damage the board itself, the cement board lets vapor pass through, so you should apply a moisture barrier behind it to prevent vapor from soaking into your wooden wall studs. 

There are various solutions you can employ, from waterproofing the wall studs with an appropriate membrane to applying a waterproofing coat to the cement board after you’ve installed it.

In the latter circumstance, don’t forget to seal the joints first and the rest of the board after to prevent moisture from passing through. 

Moisture Resistant Greenboard

Greenboard is a term used when referring to moisture-resistant drywall. This type of drywall is called greenboard because the boards are green in color (just as mold-resistant drywall is blue in color). 

Due to the moisture-resistant in its name, some people believe that it is suitable to use in showers without treating it in any way. However, while greenboard is more resistant to moisture compared to standard drywall, it isn’t designed to use in areas that experience a great amount of water, such as your shower stall.

In other words, you will still have to waterproof it for use in the shower. You can waterproof greenboard in the same way you’d waterproof any other type of drywall or cement board.

5 Reasons Why It’s Important To Make Drywall Water Resistant

Considering that drywall isn’t very expensive and waterproofing requires time and resources, you may be tempted to skip this step. However, waterproofing is important for several reasons. 

Prevent mold and mildew damage

Unless you’re installing mold-resistant drywall, mold and mildew will start growing on the drywall panel as soon as moisture passes through the tile. Mold growth in your bathroom is more than a mild annoyance. In addition to stains, it can affect your health.

Things are even worse if you or someone in your family suffers from allergies. Mold can cause serious respiratory problems and trigger asthma attacks

A waterproof coat prevents moisture from soaking into the drywall, keeping your bathroom dryer and reducing the risk of mold and mildew growth. 

Protect your wall structure 

Vapors soaking into drywall rarely remain there. In most cases, moisture will work its way into the internal structure of your walls, soaking the wall studs. 

Since wood is an organic material, the studs will eventually start to rot, compromising the stability of the entire wall. 

For this reason, you should always install a waterproof barrier between the shower panels and the internal structure of the wall, waterproof the wall studs with a specific membrane, or waterproof the drywall in your shower.

Prolonging your shower’s lifespan

In most cases, drywall in a shower only acts as a support for the tiles. What you may not know is that moisture can work its way through the grout into the drywall. 

Drywall is made of a gypsum core covered in a type of paper. The paper layer can swell due to moisture, detaching from the tile adhesive. Without the support, the tiles will eventually fall off. This is one of the main reasons why waterproofing the drywall panels before tiling your shower stall is essential. 

In addition, the gypsum layer can also become brittle in time. As mentioned above, drywall isn’t very expensive. However, replacing drywall panels is messy and requires time. Thus, you can save yourself the hassle and waterproof the boards before tiling them.

Prevent bad odors 

We already mentioned the mold and mildew. In addition to these microorganisms, a constantly moist environment also provides the perfect place for bacteria to thrive. All these germs combined represent a health risk and could cause foul odors in your bathroom.

Save money on repairs

Lastly, waterproofing drywall may mean that you have to wait for a day or two before tiling the shower stall, but it can save you a lot of money on repairs.

As mentioned above, drywall that lets moisture pass through can lead to numerous problems. Perhaps the costlier is a damaged wall structure that would require you to replace the wall studs, but retiling a shower stall is also costly.

Drywall panels are affordable, but if you don’t know how to replace them yourself, paying a contractor can take a fat chunk out of your budget. 

Getting rid of mold is also costly, especially if you have to hire a specialized team to deal with the problem. Moreover, you may have to repaint the entire bathroom to get rid of the bad odors. It’s easy to understand that waterproofing the shower stall drywall is cheaper and less of a trouble.

Related Questions

You now know how and why to waterproof the drywall for your shower but still have questions? Check out the answers below.

Can you tile over Sheetrock in a shower?

Sheetrock is a specific drywall brand often used in high-humidity environments, such as bathrooms and kitchens. According to its manufacturers, tiling over Sheetrock is safe in areas such as behind your sink but should be avoided in areas exposed to excessive wetness, such as your shower stall or around the bathtub

The reason why you should avoid tiling over Sheetrock in these areas is that moisture will eventually penetrate under the tile layer, possibly causing mold problems, damage, and pest infestations. 

That said, you can tile over Sheetrock in a shower if you take all steps to waterproof the panel’s structure beforehand, as explained in this guide.

Is RedGard paintable?

Painting over RedGard is not recommended, as it will void the warranty the product comes with. Moreover, some paint products may not adhere to RedGard. However, if you plan to use RedGard to waterproof your shower walls, you may as well paint over it or tile the wall after you’ve applied the product.

For the best results, you should use a 2-in-1 paint and primer. One-coat products tend to work best, but it is possible to apply two coats and still obtain great results.

Is mold-resistant drywall worth it?

Yes, mold-resistant drywall is worth it. These drywall panels are infused with a fungicide and bactericide mix that prevents mold and bacterial growth even if the panels are soaked in water. Generally, you can expect about 20-25 years of lifespan without a waterproofing coat. 

Comparatively, standard drywall may need replacement after only 5-10 years if you install it in your shower and don’t waterproof it before tiling.

Final Thoughts

Waterproofing the drywall in your shower is crucial if you don’t want to replace the stall after a few short years. An elastomeric waterproofing membrane is your best choice, but you could also use a waterproof primer. In addition to waterproofing, you should also install mold-resistant drywall for a longer lifespan. We hope this guide can help you carry on with the task like a pro.

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