Tile on Concrete?

Started by hpinson, May 31, 2017, 01:10:00 PM

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hpinson

I am redoing 2 bathrooms.  Currently we have vinyl tile on concrete in both, and I want to replace the vinyl tile with ceramic tile.  The concrete underlayment is smooth, flat, and 30 years old, and in excellent condition.

Do I thinset the tile directly to the concrete floor, or would be better to install some underlayment on top of the concrete and thinset to that?

Also, any opinions about using Georgia Pacific DensShield as tile backer in the tub shower? I am tending towards that, and read good reviews, in that it is quite waterproof, and easier to work with than cement board.

MountainDon

Ceramic tile on a concrete slab in good condition is fine. No need for anything else other than thinset.

I've never used Denshield, but that and the product by Ditra or Schluter all read like being superior products.  I have a shower plan about 2 years in the future.
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glenn kangiser

The only time I used a vinyl slipsheet underlayment to put the thinset on was in going over a wood floor.  The wood changes width too much during seasonal moisture changes.  This was a successful remedy. :)
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hpinson

Good reference. I will look for it. Thanks Nathan.


ChugiakTinkerer

#5
You want to make sure your slab is dry.  Sometimes moisture can migrate through the slab and into the house, in small quantities that it is never noticeable.  But it can effect the quality of the tile job.  One thing you can do to check is put a piece of plastic down on the slab, duct taped at the edges, and leave it here for several days.  After a while peel it up and see if any moisture accumulated.

Another great resource on tile is the John Bridge forum.

John Bridge is a bit of a proselytizer for Schluter Kerdi products, but having used the membrane on a bath retile I can see why.  The stuff is amazingly tough and waterptoof yet still easy to work with. 

EDIT: Forgot to mention, if there are any cracks in the slab you should consider an underlayment to decouple the tile from the slab.
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hpinson

Wow. 1110 viewing that John Bridge Forum at 8AM on a Friday morning...

busted knuckles

I used some Schlueter waffle type underlay on a concrete floor before putting tile down. Did I need to? Not sure. It was easy and not very expensive. I believe it helps prevent cracking (to a degree) from affecting then tile/grout. And preventing moisture from coming through.
you know that mugshot of Nick Nolte? I wish I looked that good.

Mike 870

Another thing to watch out for, is test how thirsty the slab is.  In some cases it can suck too much moisture out of your thin set and cause failure.  Otherwise Concrete is a great substrate.


hpinson

Mike 870 - the slab does seem thirsty. I was cleaning it last night, and when sponging, it was clearly pulling in moisture.  What would be recommended in that case. Some sort of sealer first?

NathanS

#10
Just a few notes from the TCNA handbook I mentioned earlier. They show 24 methods for installing glass or ceramic over an interior slab floor. Another 11 for slabs with radiant heat in them. Then another 21 ways for natural stone over interior slabs.

Quick flip through, mostly they just say about slabs - "Slab to be well cured, dimensionally stable and free of cracks, waxy or oily films, and curing compounds." Edit: Also saw "Slab to have steel trowel and fine broom finish free of curing compounds. When used, mechanical scarifying is necessary."

In my opinion make the slab moist when you put down the thinset, that will give it something to stick to. If you use a membrane to waterproof it, I liked using redgard. It goes on fast.

hpinson

well cured: check

dimensionally stable: check

free of cracks: check

waxy or oily films: has remnants of vinyl tile mastic which I am having to remove with Goof Off

steel trowel and fine broom finish: check

I will be using something like Redguard on the tub surround waterproofing - Latecrete Hydro Barrier membrane - would that work as well?

Or would just moistening the concrete surface as NathanS suggests be good enough?


NathanS

I hadn't heard of concrete absorbing water too fast before, not to say it couldn't be an issue. I have heard the opposite concern when pouring a slab, that if you have poly underneath it that it can only dry upwards and more likely to cause cracks. No idea if that's true, but on the west coast they started putting wet sand in between the concrete and the poly, theirs didn't crack either, but now for the next 15 years you can't put anything relatively vapor closed on the slab cause it will cause mold and mildew. Anyway, it really seems like with masonry and a lot of the trades if you ask 10 people how to do something you will get 20 answers, and they all might be right because if it works, it works. Even the TCNA handbook has like 50 ways to do tile on a slab because there are so many methods that work just fine.

Something like Redgard or a hydro barrier is really just for waterproofing the floor. I'd personally be more worried about that on a second floor, or over wood where you want to minimize expansion and contraction.

I bet that if you look at actual tile failures (cracked grout or popped tile) 99 times in 100 it's because there is too much deflection in the floor, either parallel or perpendicular to the joists.

Mike 870

Yea it's a real thing, if too much water is absorbed out of your thin set prematurely it won't cure to proper strength.  Not all that common but it happens with slabs, wonderboard, durrock etc.  redguard, aquadefence can be a safe preventative measure.  Sorry for the late reply.


UK4X4

Seal the slab before tiling, use PVA or similar or other wise the concrete wicks out the strength from the tile cement......in the UK we have mostly brick and concrete construction and we copiously use PVA everywhere to get correct adhesion of cement/glues/tile cement even wall paper !

I had two lots of render fall off my house due to the lime and sand cement wicking all the goodness out of the concrete..we then did 3 copious layers of pvs mixed with water until the whole wall was sealed...the last set of render has lasted almost 20 years with no cracking as yet !



hpinson

UK4X4 I looked up PVA - is this what you mean:

KILZ 1 gal. White Flat Interior PVA Primer-PX01001 - The Home Depot

http://www.homedepot.com/p/KILZ-1-gal-White-Flat-Interior-PVA-Primer-PX01001/202837010

I'm going to start a separate thread on this soon - completely redoing a bathroom, and this is just one part of what I'm encountering. I'm actually still pretty far away from tiling, but am preparing.

UK4X4

In the UK its a PVA glue/ sealer waterered down for use similar to this
http://www.screwfix.com/p/unibond-super-pva-glue-5ltr/29912

However googling it some people have had issues with PVA and certain tile glues.....

I just did my UK house kitchen floor but on a wood base and used the sealer recommended by the tile glue manufacturer

the one you posted seems to be a PVA based paint,,,not sure it would soak in,

This is the one I used on my kitchen floor

http://www.screwfix.com/p/mapei-primer-g-5kg/5309p?_requestid=322546

along with mapei tile glue.

So maybe worth looking at what tile adhesive you want to use and choose a sealer that is recommended by that supplier....

here is an example in the states...http://www.homedepot.com/p/Henry-336-1-gal-Bond-Enhancer-Self-Stick-Tile-Primer-12056/202046165