Issues with Tiling Over Old Concrete Slab—Looking for Advice

[JustinScott]

Hi everyone,

I’m working on a tiling project over an old concrete slab, and I’m running into some concerns about adhesion and long-term durability. The slab itself is structurally sound, but there are a few hairline cracks and some slightly uneven areas that have me wondering about potential problems down the line.

Here’s the situation: The concrete was previously used as a garage floor, so it’s had exposure to oil stains, moisture, and heavy traffic over the years. I cleaned the surface thoroughly, but I’m unsure if there’s still any residual contamination that could affect the bond. I haven’t applied any primer or moisture barrier yet because I want to make sure I take the right approach before committing.

Has anyone here tiled over a similar surface? Do I need to do anything special to prep for adhesion, or will a standard thinset work fine? I’ve also heard mixed opinions on whether an uncoupling membrane is necessary when working with concrete that has minor cracks. Would it be overkill, or is it worth using to prevent future issues?

Thanks for any help!

 

[JustinScott]

Hi everyone,

I’m working on a tiling project over an old concrete slab, and I’m running into some concerns about adhesion and long-term durability. The slab itself is structurally sound, but there are a few hairline cracks and some slightly uneven areas that have me wondering about potential problems down the line.

Here’s the situation: The concrete was previously used as a garage floor, so it’s had exposure to oil stains, moisture, and heavy traffic over the years. I cleaned the surface thoroughly, but I’m unsure if there’s still any residual contamination that could affect the bond. I haven’t applied any primer or moisture barrier yet because I want to make sure I take the right approach before committing.

Has anyone here tiled over a similar surface? Do I need to do anything special to prep for adhesion, or will a standard thinset work fine? I’ve also heard mixed opinions on whether an uncoupling membrane is necessary when working with concrete that has minor cracks. Would it be overkill, or is it worth using to prevent future issues?

Thanks for any help! https://www.concretesrichmondva.com/

Just realized I didn’t check whether the concrete was sealed in the past. If there’s an old sealer still on the surface, could that be affecting adhesion? I know some sealers can cause bonding issues with thinset, but I’m not sure how to tell if it’s still present. Has anyone dealt with this before? Would lightly grinding the surface be necessary, or is there another way to ensure proper bonding?

 

[Kastar UK]

do a test with scrap tile see if can pull it up the day after ?

 

[JustinScott]

do a test with scrap tile see if can pull it up the day after ?

Good idea! I’ll try a test tile and see how well it bonds. If it pulls up easily, would you recommend a different adhesive or surface prep method?

 

[Kastar UK]

Good idea! I’ll try a test tile and see how well it bonds. If it pulls up easily, would you recommend a different adhesive or surface prep method?

I cant see it an photo no good i cant feel it

Tile bonded to adhesive ?
Adhesive bonded to unknown ?
unknown bonded to concrete ?

Depends where fails first when taking back up the sample ?