[Kellytacy2]

Hi there. Quick question on laying tile on (above grade)concrete slab.

I have done a few DIY tile projects (baths and one kitchen)but always on hardi-backer that was laid on subfloor/wood/OSB. We have a backbathroom in house we just bought that has bare concrete. I can tell some floorcover was there before which has been removed. Assume tile but can’t be sure.

Anyway, its at/above grade and in good shape (maybe 10 yearsold). No cracking, just a few once I get it cleaned up (rough patches or whatlooks like could be adhesive). Can I tile right on top of it? Would be usingprobably porcelain/ceramic 12x12” or 12x6 inch or smaller tiles. Do I have toput hardi- backer down? Or any crack prevention membrane (like redguard I usedonce years ago, though we were “Below grade”). Thought I don’t see any cracks Ijust have never laid right on concrete and while the pad is at least 10 yearsold, could it still expand and contract and cause tile or joint failure?


Welive in Charlotte North Carolina so while we do abut an exterior wall here, Idon’t have freeze or flood concerns here in winter.

 

[nld09]

I don't see why not. I have done it a few times (3x) and didn't have any issues with it. I am just a diyer so I could be wrong though.

 

[chandler48]

It will be fine. I don't know how else to do it, unless you have cracks. Then you would pop the cork on a bunch of Schluter membrane, but I doubt it would be called for in your situation.

 

[Brother Antioch]

If you use a good modified thinset you should be fine, so long as there are no cracks in the concrete, and there is no paint or similar finish to the concrete. If there is, the thinset will bond to the paint and not the concrete, and will fail.

Cheers,

BA.

 

[Brother Antioch]

It will be fine. I don't know how else to do it, unless you have cracks. Then you would pop the cork on a bunch of Schluter membrane, but I doubt it would be called for in your situation.

Personally, I've found Laticrete Blue 92 is a MUCH better option than using Ditra. Similarly, I use Laticrete's Hydroban for waterproofing a shower rather than Kerdi mat.

There's much better choices than Schluter on the market for around the same price point, but it's like a Corvette vs. a Bugatti Veyron...just because most people have heard of a Corvette, doesn't make it a better sports car than the Veyron.

Cheers,

BA.

 

[akeyes]

I recently tiled over concrete (in a basement tho). Used the Schluter Ditra underlayment. It all worked great, but I'm not sure it was really necessary. One thing that could help you decide is the height of the surrounding flooring / baseboards / etc. If you 'need' to raise the subfloor a bit, then it's an easy fix to add some type of underlayment/membrane, instead of laying it directly on the concrete, then having to add quarter round or remove and replace baseboards and whatnot.

On the other hand, the membrane will give you a lot of confidence that the tile will last for a really long time with no cracks or gaps. If it's a small(ish) area, and you can get away with just one roll of the membrane, I'd say go the extra step and add another layer or protection. So, there's that

 

[jeffnc]

Personally, I've found Laticrete Blue 92 is a MUCH better option than using Ditra.

They are not even close to being the same thing. And how exactly is Laticrete Blue "MUCH" better than Ditra?

There's much better choices than Schluter on the market for around the same price point

What is a "much better" choice than Schluter Ditra, for example?

 

[jeffnc]

You will probably be fine just going over the top of it. Of course there's no guarantee it won't develop cracking in the future. I guess it depends on how much you can count on "probably". If I were doing this in someone else's house, I would use Ditra underneath (or similar). (HardiBacker or other cement board buys you nothing in this case.) If I were doing this in my own house, I might skip the Ditra.

 

[udraft]

Concrete would be a preferred surface for hard tile. Hardi-backer and the like are really trying to be concrete. Even some settling cracks will not hurt a thing, as long as it's solid and done settling.
Just be sure the surface is clean and dry. Old black mastic, if enough is there, can seep up thru the grout joints. We like to let fresh concrete cure for a while, but an old slab in good condition is ideal. TSP can be used if it needs cleaned.

 

[Brother Antioch]

They are not even close to being the same thing. And how exactly is Laticrete Blue "MUCH" better than Ditra?

It allows you to use a full modified thinset, as required for almost all floor tiles these days, as ceramic tiles are pretty well used only on walls. It's thinner than Ditra. The mesh laid into the rubberized compound provides even more elasticity. This is tile setting 101...

What is a "much better" choice than Schluter Ditra, for example?

I get it. You must belong to the Church of Schluter. But what makes you think Ditra is the be-all and end-all of substrates? I use hardie backer board, screwed to the wooden subfloor. It adds rigidity, it sets me up for the perfect level to meet with 3/4 wood floors, and it allows me to use the proper mortars (ie: full modified) which is verboten with Ditra.

Then there's the cost...hardie board is almost 1/2 the price of Ditra, and in my professional opinion is a superior product. In ten years of using it, I've never once had an issue or a call back, but I've seen nightmares when people use Ditra improperly, or try and use a modified thinset for porcelain tiles or natural stone. Unless you have 30 days to let it sit before grouting, it's simply the wrong choice, period.

And on a side note, why so adversarial?

 

[jeffnc]

It allows you to use a full modified thinset, as required for almost all floor tiles these days

We've been over this before. You're just not listening.


For one thing, modified thinset is NOT "required" for tile floors. You use the thinset that holds strongest. When thinset can dry well, modified thinset is better. When thinset can't dry well, as when trapped between a waterproof barrier and porcelain tile, then a thinset that does not need to dry to get to full strength is better - i.e. unmodified thinset.


Second, Schluter does allow modified thinset, but only certain ones are formulated to reach high strength without needing to fully dry, such as Schluter All Set. They warranty that because they know how it's made. They also warranty rapid set thinset, which is polymer modified. Otherwise, use the cheaper unmodified thinset (although a good quality one obviously). They also warrenty these unmodified thinsets.

I get it. You must belong to the Church of Schluter. But what makes you think Ditra is the be-all and end-all of substrates?

I don't, and I don't. We've been over this before too, but you're not listening. I don't think Ditra is particularly better than most other uncoupling membranes (although it is a waterproof solution, so there is that if you need it.) You're the one who said there are MUCH better options out there, so the onus is on you to prove it. I'm saying there are not, or there are minor differences one way or the other.

I use hardie backer board, screwed to the wooden subfloor. It adds rigidity

We've been over this before, but you're not listening. Backerboard is NOT a structural element.

it sets me up for the perfect level to meet with 3/4 wood floors

Only when it does, and not when it doesn't. Sometimes it's too high and that's when you want 1/8" Ditra to match a lower height. Or maybe 5/16" Ditra XL matches the height better.

and it allows me to use the proper mortars (ie: full modified) which is verboten with Ditra.

You're not listening very well, again. This is incorrect.

Then there's the cost...hardie board is almost 1/2 the price of Ditra, and in my professional opinion is a superior product.

It offers no structural support, no uncoupling, and no waterproofing. How the heck is it superior? Is it good enough? Sure, often it is. Add in the cost of the screws and the price isn't quite as good. But it doesn't do what uncoupling membranes do.

We've In ten years of using it, I've never once had an issue or a call back, but I've seen nightmares when people use Ditra improperly

So what you're saying is that backerboard installed correctly works well, and Ditra installed poorly does not work well? Big deal! I'd go so far as to say that tile installations done well work well, and tile installations done poorly don't work well.

And on a side note, why so adversarial?

Because we've been over all this before, and you're not listening. You're close minded, opinionated, and as far as I can tell unwilling to listen, learn, or do any new research. So there's no need for you to be misleading DIYers. And speaking of DIY, Ditra and other uncoupling membranes like it (which we have gone over before, Mapei, Laticrete, et al) are FAR easier to carry, cut, and install compared to backerboard. (Not even mentioning the additional benefits of uncoupling, and if necessary waterproofing.)