How to Waterproof a Concrete Roof

A roof terrace with concrete tiling.
  • 3-6 hours
  • Beginner
  • 75-300
What You'll Need
Push broom
Dust pan
Masking tape
Silicone caulk
Caulking gun
Putty knife
Seam tape
Concrete primer
Paint roller
Vapor barrier
Paint sprayer
Concrete paint (optional)

Concrete rooftops are usually built on commercial buildings, however, flat concrete roofs and concrete shingles have been gaining popularity for use in constructing private homes. Still, even if this material does afford a much longer life than other choices, it is as susceptible to the elements as any other material. Adding a waterproof coating will help offset this downfall and allow your roof to last much longer. The following article will show you how to properly accomplish this task yourself.

Step 1 - Clean Your Roof

In order to successfully seal your roof, you first need to start with a clean surface. Use a push broom and dustpan to remove any dirt or debris. Take your time so you can do this thoroughly — anything left behind can cause your sealer to not adhere well.

Step 2 - Carry Out Minor Repairs

Concrete can crack and produce leaks just like any other type of roofing material, but it is easier to repair by far. These areas are prime spots for water to further erode the concrete, so inspect the entire surface for any damage first. Mark off any damaged areas you find with masking tape so they are easy to find again. Then use silicone caulk in a caulking gun to fill in the cracks, breaks, or holes. Use a putty knife to smooth out the sealant as well as to push it further into the area. Repeat this process until you are confident that the imperfection is completely sealed. Allow the silicone to dry before you move forward with waterproofing.

Step 3 - Use Seam Tape

Priming actually helps in the waterproofing process, but before you can add it, you will need to cover any seams in the concrete with seam tape if possible. Use a single piece wherever you can, and make sure it is centered over the seam when you put it down. Walk on the tape after it is laid to press it down further for the best hold.

Step 4 - Coat With Primer

Next, apply a coat of concrete primer to the entire roof. Start at one end and paint yourself into a corner; then, switch to a paintbrush to finish. Wait for the primer coat to dry completely before you determine whether you will need a second. The proper dry time should be indicated on your product label, so consult these instructions if you're unsure.

Step 5 - Spray on a Vapor Barrier

Pour your chosen vapor barrier into a paint sprayer after the primer is dry, and liberally spray an even coat onto the concrete roof. Work systematically from one end to the other, spraying in lines. Overlap the previous line every time you start a new one. Allow the vapor barrier to dry before you add a second coat. Then, after your final coat dries, you can choose to paint over it if you would like.