How to prepare concrete floor for waterproofing?

[Madelon]

Hi, I am preparing my shower & toilet room flooring for waterproofing. It is only a small area, but there are some dents (from removing old tiles and glue and rougher patches in the concrete. I believe for the waterproofing the Crommelin range will be used, but should I do something to fill in the dents and remove the rougher patches first? I can't increase the floor level much as it opens to an already tiled area which will be flush once the tiles are installed on the floor... Thank you so much for your help.

[MitchellMc]

Hi @Madelon,

Yes, it’s a good idea to prepare the concrete as smoothly as possible before applying waterproofing. Small dents and rough patches can create weak spots in the waterproofing membrane or paint, and they can also make tiling harder later.

For shallow dents or glue residue, you can use a thin patching compound designed for concrete floors. Apply it lightly just to level out the dips or fill the rough areas, and make sure it dries fully before waterproofing. Avoid adding too much thickness, since you want the floor to stay flush with the adjoining tiled areas.

Once the surface is smooth and clean of dust, grease, or loose particles, you can proceed with the Crommelin waterproofing. A well-prepared substrate will help ensure a continuous, durable waterproof layer.

Please let me know if you have any questions.

Mitchell