Tile onto concrete: need pointers

[whiskeyjack]

I've decided to re-tile our 1/4 bath as a learning experience.  It's a small area that I thought would give me a feel for it.   We've pulled the old vinyl up and repaired the 'interesting' toilet plumbing installed by the builder.  (6 wax rings!)

Now I've got all the vinyl up and I'm scraping up all the bits of residual glue and what looks like paper.   My first question is: how pristine does this floor need to be?   I'm pulling up anything I can feel but if there is something left that looks white and not the gray of the concrete, but I can't feel it, do I need to get a wire brush and scrub it off?   I've hit it with a wire brush drill attachment and it will come up that way, eventually, but I'm not sure what it is I'm taking off at this point.

Second question:  I'm going to pour a thin layer of self-leveling compound to even everything up and fill some small holes.   What should I use as a barrier to stop it from running under the drywall?   Cardboard?  Something that won't stick to it?  Just thin it out at the edges?

YouTube has been letting me down on these points!

Thanks for your help.

[lthenderson]

For floors I just scrape up the loose stuff and don't worry if the floor isn't pristine concrete to tile over. I would be more concerned if it were walls or a ceiling.

For sealing cracks before self leveling, I just use caulking and foam depending on size of the cracks.

Try as I might, I can't even imagine a scenario where six wax rings could be used even if one wanted to use that many. How I wish you had a picture you could post on here of that situation.

[whiskeyjack]

I don't have a proper level - just a 2 foot one, but laying that down I can find some areas with 1/4" of gap.  The whole bathroom is only 5x5'.   The other holes aren't cracks exactly but 1cm holes drilled into the slab by the anti-termite folks.   I wasn't sure how to best deal with that.   Is that too much for the thinset to handle?  I was also thinking that if I put down a smallish tile/mosaic it would be more forgiving of some unevenness.

I'll stop trying to wire wheel the crud off the floor.

And I'm sorry I didn't take a photo!   The toilet never sat quite flat and once we pulled it up it was because the drain was installed well below the slab and they'd cut out a hole around it wider than the base of the toilet, then propped it up below the vinyl with some scrap wood which had started to shift/rot over time.  The stack of wax seals was to make up the height difference.  Somehow it didn't show any signs that it had been leaking.  (I've been corrected - there were only 4.  I guess it just looked like more to me.)

[kendallf]

I don't have a proper level - just a 2 foot one, but laying that down I can find some areas with 1/4" of gap.  The whole bathroom is only 5x5'.   The other holes aren't cracks exactly but 1cm holes drilled into the slab by the anti-termite folks.   I wasn't sure how to best deal with that.   Is that too much for the thinset to handle?  I was also thinking that if I put down a smallish tile/mosaic it would be more forgiving of some unevenness.

I'll stop trying to wire wheel the crud off the floor.

I'd put the self leveling stuff down if it's 1/4" or more out of level.  You can probably compensate with thin-set, but it'll be easier if it's flat.  Stuff something into the gap between the drywall and the floor, and then pull it out when the pour sets up a bit.  I'd avoid bridging the gap to the floor with caulk or anything that might let water wick up the drywall later.  The 1 cm holes won't matter, the thinset will have grooves from your trowel that are almost that big.

[whiskeyjack]

I don't have a proper level - just a 2 foot one, but laying that down I can find some areas with 1/4" of gap.  The whole bathroom is only 5x5'.   The other holes aren't cracks exactly but 1cm holes drilled into the slab by the anti-termite folks.   I wasn't sure how to best deal with that.   Is that too much for the thinset to handle?  I was also thinking that if I put down a smallish tile/mosaic it would be more forgiving of some unevenness.

I'll stop trying to wire wheel the crud off the floor.

I'd put the self leveling stuff down if it's 1/4" or more out of level.  You can probably compensate with thin-set, but it'll be easier if it's flat.  Stuff something into the gap between the drywall and the floor, and then pull it out when the pour sets up a bit.  I'd avoid bridging the gap to the floor with caulk or anything that might let water wick up the drywall later.  The 1 cm holes won't matter, the thinset will have grooves from your trowel that are almost that big.

Does the SLP set up 'a bit' fast enough that I'll be able to pull the barrier out before I've finished pouring the whole floor?  In my head I'm imagining trying to lean in from the door and pull it all out at once and I'm tall, but not that tall.

Thanks again.

[kendallf]

Does the SLP set up 'a bit' fast enough that I'll be able to pull the barrier out before I've finished pouring the whole floor?  In my head I'm imagining trying to lean in from the door and pull it all out at once and I'm tall, but not that tall.

Thanks again.

No, not particularly.  I was meaning just use something flexible like wadded up paper or the like, then pull it out after it sets up.  If the self leveling compound won't reach the drywall, I wouldn't worry about it anyway; there's presumably a base plate for the wall behind the drywall that will stop the mud there.

[meghan88]

Check out the John Bridge tile forum:  http://www.johnbridge.com/vbulletin/ - there are a lot of really good people on there who are happy to help with advice.

You might consider putting a decoupling membrane such as cement board or Kerdi over the concrete.  Often, tiling directly onto concrete will result in cracks in the tile and/or grout.

Also, for floors, it always makes sense to use plain old grey grout.  Whatever you do, don't use white grout on a floor, ever.  Or light beige.