Filling a hole in a cement floor before tiling

[dutts]

Apologies if this should be in a different forum, but I am ultimately going to be tiling this area.

I have ripped out our downstairs cloakroom to decorate, tile the floor and put in a new suite. Unfortunately as I was trying to remove the toilet, the screws fixing it to the floor had been covered with something that looked like cement and needed to be drilled out of the screwholes, after a good hour or so of trying to drill out the screws with no luck we ended up just taking a crowbar to it to lever it off the floor which has taken a chunk of floor with it as shown in the picture. The cloakroom is on the ground floor, I think the floor is cement. The black tile-looking things in the picture are actually the sticky black stuff that was fixing the original vinyl floor tiles which where under the carpet.

Untitled

• dutts
• 26 Jun 2012
• 1

The crater is a bit smaller than the size of a toilet base and upto 5mm at its deepest.

I was wondering what would be the easiest material to fill this with? I am going to be laying 9mm thick floor tiles and then there will be a toilet in the same position.

Would cement be ok?

Thanks in advance

Richard

 

[Karis]

Fill it out flush with cement powder based tile adhesive just before you tile & use powder adhesive to tile not tub mix. You need to prep that bitumastic coating before tiling or you will have problems.

 

[dutts]

Ahh bugger, thanks for pointing that out. It's horrible stuff, what can I do with it?

 

[Karis]

It’s not recommended to tile over bitumen adhesive & the problem is the stuff is almost impossible to remove by mechanical or chemical means, it just goes soft. Most adhesive manufacturers sit on the fence & won’t recommend tiling over it or guarantee their products over it.

The only bullet proof approach would be to put down a self leveling screed & then tile over that but you can prime with a cement/SBR slurry coat. Scrape off the thicker/uneven/loose bits but don’t use a heat gun or solvent as this will soften/reactivate the bitumen & risk a reaction with the adhesive. Prime the floor with a Portland cement/SBR primer slurry coat – ratio 2:1. Check it’s bonded well when dry & there is no bleed though before tiling & use a flexible tiling adhesive. I’ve heard of some priming with Ardex P82 primer but I’ve never tried it.

 

[dutts]

hmmmm ok this might have turned into a bigger job than I had intially hoped!

I feel a bit of an idiot now as I actually removed the thin plastic tiles which were covering this after taking the carpet up, some of them had been damaged by the removeal of the toilet so I fuigured it would give me a cleaner surface.

For future reference so I know if I come across these in other parts of the ground floor of my house, would I have been better leaving them down and tiling on top of the plastic tiles?

I have read elsewhere on this forum that a latex slc spread over the top would be ok?

 

[Karis]

You can tile over old vinyl tiles but they must be sound & the original bonding must be in no doubt. No need to feel like an idiot as IMO removing the old vinyl tiles was the right thing to do & is what I would always do. You can use a latex SLC & this is the bullet proof option I refer to in my post. The cement/SBR slurry primer is a much cheaper alternative & works but I obviously won’t give you a personal guarantee.

 

[dutts]

Thank you so much for your help mate, much appreciated.