Concrete – Only apply primer to concrete roof


Our building has decided to paint a 13-ft x 13-ft section of the roof that's leaking (just a few drops with lots of rain). This roof has a fence since it's an "outdoor" area that we all share, so it's secure to work there. We live in the Caribbean, so this roof receives lots of sun. The roof is not covered.

Someone went over there to quote the job, and he said that he would apply a primer and then an "ultra-white" roof coating. I was checking in home depot, and most (if not all) roof coatings are very white.

So my questions:

Since we don't need the roof coating to reflect the sun or UV rays, is it possible to just apply a very good/thick primer and that's it? Many years ago they applied a white roof coating, and it was so bright that we couldn't sit up there.

We only need a product that will seal the concrete and stop leaks. I don't know much about this, but I was thinking of something like a Satin Clear Seal Concrete Protective Sealer or a Water-Proofing Membrane. Whatever we apply, it can't be a bright white.

The ideal product would have the following characteristics:

  • Seals the concrete and stops the leaking
  • Since the concrete is very rough, it'd be great if the coating's thick enough so that the concrete doesn't fill so rough if someone falls.
  • If the product has some color, that'd also be great. But it's OK if it's clear. It cannot be ultra-bright white.

Best Answer

You really need a sealer. White is chosen to reflect the heat AND this will last longer than black. When we used hot tar on roofs we then painted them silver or white. If we did not do this the tar would end up in puddles.

Primers are made to seal wood and wall coverings, not a concrete roof. You need a coating with some “body” that maintains flexibility and don’t go cheap, get it sealed before it gets worse. Multiple coats may be needed but a quality product will probably work with one coat based on your description.

So get the right product for the job and don’t go cheap.

Edited: I noticed the link for the Elasto lock , read the instructions this product suggests power washing, they mention acid etching to clean newer pours and do not mention primer at all. DO NOT USE PRIMER WITH THIS PRODUCT!. It needs the porosity of the concrete to bond as I have mentioned in several comments. But I believe it would be a good product to use to seal your leak. As I have not used the satin sealer in the original question I looked up some info. A question was asked about a concrete roof leaking here is rustolium’s response:

Rust-OleumSupport March 04, 2019 Thanks for reaching out, Richard. Rust-Oleum Sealkrete Clear Seal Concrete Protective Sealer will offer waterproofing qualities, but you may need to consider two coats for adequate coverage. You will get 150-300 sq ft of coverage and you can recoat the product in 2 hours. - Rust-Oleum Product Support 1

So so as I said I would not use that sealer it only had sealing properties, but the ElastO lock you linked to looks like a good flexible product made to seal cracks. And no priming is required but cleaning is.