How To Waterproof Drywall in Garage (Complete Guide)

An important thing people overlook when working on their garage is waterproofing their drywall. While waterproofing drywall in your garage isn’t necessary, it’s an important step. After all, your garage is at risk of water entering during rains, which can cause significant damage to your floor and walls.

How to Waterproof Drywall in Garage

You can use waterproof paint and primer or water-resistant drywall. You may also want to apply a waterproof membrane, fiberglass-reinforced plastic (FRP), or use non-drywall materials in your construction.

Let’s look at each of these options in further detail. By the time you’re done with this article, you’ll have extensive knowledge on how to protect the drywall in your garage from water.

This will ensure you’ll have significantly less maintenance work you’ll have to do in your garage after the rains for years to come.

1. Use Waterproof Paint and Primer

A waterproof primer is the most popular solution for waterproofing the drywall in garages. It’s also the easiest.

Waterproof paint and primer is exactly what it sounds like – a waterproof paint and primer you can use to paint your drywall and protect it from water.

Most brands roll their waterproof paint and primer into a single solution, so you only have to paint an area once.

Here’s how to use these materials to protect your garage:

1. Choose the paint and primer in your chosen color.
2. Clean the drywall in your garage thoroughly, especially the areas when the paint and primer will be applied. You should use both a dry and wet cloth when cleaning the drywall to ensure no microscopic debris is left behind.
3. Check the paint/primer label to see whether it can be used on a wet surface or not. If the paint requires the surface to be dry, allow the drywall to dry completely. If not, you can start working immediately.
4. Use the paint and primer to paint the garage area you want to protect from the water. Both oil and latex-based options are readily available, and you should easily be able to find the paint/primer of your choice at your local hardware store or online.
5. Paint a thin, even coat of the paint/primer with a roller. Apply the primer to harder-to-reach areas like corners with a paintbrush.
6. Allow the paint/primer to dry.

If you use two different products – a waterproofing paint and a waterproofing primer – first paint the drywall with the primer.

Once the primer has dried, paint over it with the waterproofing paint. You can use the method described above when using both the primer and the paint.

Waterproof paint and primer will protect your drywall from dampness, mold growth, and mildew growth. A good primer will stay in place between two and five years before it needs to be reapplied.

However, if you’re unsure how long your chosen paint/primer will last, ask the sales associate or check if there are guidelines on the paint bucket.

Alternatively, you can perform an annual check on the status of the paint/primer. Choose a small spot of the drywall and pour a little water on it to see how the coating reacts. You can easily tell whether it is still waterproof or if you need to do a touch-up.

2. Use Water-Resistant Drywall

Perhaps the simplest way to “waterproof” your drywall is to use water-resistant drywall instead of regular drywall in your garage.

Water-resistant drywall is pretty self-explanatory. Like regular drywall, it is made with gypsum and can attach to studs.

However, it generally comes with sea-foam green paper covering one side, distinguishing it from regular drywall. This is also what gives it its nickname, greenboard.

It should be noted that a greenboard isn’t a waterproof material. Rather, as the name implies, it is water-resistant.

Unlike other waterproofing methods like waterproof primer/paint, greenboard does not always prevent mold growth. However, some brands of greenboard are pretreated for this purpose, so it is possible to find mold-resistant greenboard.

Because greenboard isn’t entirely water-resistant, it’s highly recommended that you don’t use it in extremely wet areas of the house, such as the bathroom. However, in most cases, it should be okay to use in your garage.

Additionally, this limitation is not only limited to greenboard. Several brands of “waterproof” paint and primer are not designed to be used in the kitchen or bathroom, as the constant exposure to water will destroy their effectiveness.

When priming/painting your bathroom with waterproof paint/primer, choosing a formula specially designed for high humidity areas is essential.

Another “waterproof” drywall is purpleboard. Like greenboard, purpleboard’s name comes from the color of one of its surfaces – in this case, a light purple. Like greenboard, it’s a water-resistant drywall.

The advantage of purpleboard over greenboard is that it’s inherently mold-resistant and is also resistant to mildew. Furthermore, there are variations that can withstand dents and even act as a soundproofing material.

That said, it’s essential to keep in mind that purpleboard is a significantly more expensive product. One estimate puts the price of purpleboard at 30% over that of regular drywall.

While greenboard is more expensive than regular drywall, it’s less costly than purpleboard.

Additionally, purpleboard is only manufactured by a single company. There’s no market competition, so it’s unlikely that purpleboard prices will go down.

You can also consider blue board drywall. Also known as plaster baseboard, this drywall gets its name from the blue paper covering on one side.

This extremely water-resistant drywall is commonly used for high moisture areas, such as the bathroom and kitchen.

It has a similar price to greenboard, making it a smart option if you’re looking for something closer to a genuinely waterproof material without breaking the bank.

Blue board drywall is also a good idea if you live in an area with strong monsoons and expect a lot of rain to make it inside your garage.

Finally, there’s the case of paperless drywall. Like regular drywall, it has a gypsum core – but, instead of a paper outside, it’s covered in fiberglass.

Like the other three types of drywall, it’s moisture-resistant. It’s also resistant to mold and mildew.

The price of paperless drywall is significantly higher than that for greenboard and blue board drywall. Depending on the make and model, paperless drywall can be double or more of what you have to pay for greenboard and blue board.

Ultimately, you should consult a professional if you’re unsure which of these many “waterproof” drywall options are right for you. They’ll be able to offer you advice designed for your unique needs.

3. Apply a Waterproof Membrane

Waterproof membranes are water-tight materials that are laid over any surface you want to waterproof, including drywall. These membranes can come in plastic, rubber, or fabric coated to make them waterproof.

To apply a waterproof membrane, first, get your drywall ready. Then:

1. Clean the drywall of any dust and debris. Damp the surface of the drywall with a wet sponge – this will prevent the thin-set from setting too fast before you have managed to apply the membrane.
2. Cut the membrane to size.
3. Apply thin-set to one drywall. The thickness of the thin-set will depend on which brand you’re using – for example, for the Kerdi membrane, you will need a relatively liquid thin-set. Work on one wall at a time so the thin-set doesn’t dry out. Some membrane brands will require you to use a particular thin-set to maintain the warranty, so you should check this before applying any.
4. Smooth the thin-set such that all trowel marks are in the same direction.
5. Press the membrane against the wall, pushing it into the corners to ensure the drywall is properly waterproofed. Work your way by pressing down the membrane from top to bottom, smoothing it out so that no air bubbles develop.
6. Use a trowel or putty knife to ensure the membrane is flat against the drywall and that there are no air bubbles.
7. Pull back the membrane to check the coverage.
8. Cut away any excess membrane.
9. Seal the seams, joints, and floor-wall connections with a waterproofing strip. Most waterproof membrane brands sell waterproofing strips to be used in conjunction with the membrane. Use a waterproofing strip from the same brand as the membrane for best results.

For a better idea of how to install a waterproof membrane over drywall, check out the video below from Home Repair Tutor on YouTube:

While the video looks at the application of a waterproof membrane in a shower, the process is the same when working on your garage. The only difference is that you’ll probably not be cutting around a valve for water.

Not all waterproofing membranes are solid at application. For example, one popular waterproof membrane type is polyurethane liquid membrane, which (as the name implies) is a liquid membrane made with polyurethane.

It should be applied with the help of a roller or paintbrush. Generally, two layers of membrane and a layer of sand are applied before your surface is waterproofed completely.

4. Apply Fiberglass-Reinforced Plastic (FRP)

FRP is essentially a thin sheet of plastic resin reinforced with fiberglass. These panels can be applied over your existing drywall surface to waterproof it. They are highly moisture-resistant, so their use isn’t only limited to your garage – you can also use them in high-moisture areas like bathrooms.

To apply, here’s what you need to do:

1. Ensure the surface of your drywall is level and free of any dust and debris.
2. Cut the FRP panels to size.
3. Apply FRP adhesive to the back of one panel. You will need to coat the entire back surface with FRP adhesive (ideally in a cross-hatch pattern if possible).
4. Press the panel against the wall. Use a laminate roller to roll over each panel and remove any air bubbles that may exist.
5. Repeat this process for the next FRP panel. Remember to keep about 0.125 inches (0.32 cm) distance between each FRP panel. This ensures that when the panels expand, they’ll not overlap and start to break.
6. Seal at joints and seams with silicone sealant. If you plan on attaching trim or top molding, do so before applying sealant.

5. Use Non-Drywall Materials

If none of the options discussed above works for you, the other solution is to use a substrate material that’s not drywall.

Of course, given that waterproofing is the aim, you should choose a substrate that is waterproof, or at least more water-resistant than drywall. Some options you can consider include:

Pegboard

You can install a pegboard over the studs instead of drywall. Pegboard has pre-drilled holes that can be used to hold pegs or hooks and can also be used to hold shelving, making it a practical alternative to drywall.

Pegboard is generally made of wood or plastic, and plastic pegboard is waterproof. (While metal pegboard is available, finding it in sizes large enough to cover whole walls can be challenging).

You can also paint the pegboard in the color of your preference.

Wall Panels

Wall panels are essentially a single piece of material cut into a flat, rectangular shape. You use it to cover a wall, and it serves as an attractive alternative to drywall.

These panels are available in numerous finishes and materials, including 3D textured wall panels. Most people use these panels inside the house, but you can also use them in your garage.

Because of the variety of wall panel options available on the market, you can also find waterproof wall panels, which you can install in your garage.

The main challenge with this material is that it can be significantly more expensive than drywall. However, if you have the budget, it’s a faster alternative and results in a more aesthetically pleasing space.

Final Thoughts

You can waterproof the drywall in your garage by applying a waterproof primer and paint, using water-resistant drywall, applying a waterproof membrane over the drywall, or installing FRP panels on the drywall.

Alternatively, you can use a substrate other than waterproof and/or water-resistant drywall, such as plastic pegboard or waterproof wall panels.