# will mold form under ceramic tile?



## joecaption (Nov 30, 2011)

It's done all the time with no problums. In fact it's one of the best type floors to use in a basement.
Just do not lay a layer of tile board under it. Go right over the slab.
As long as there's not a flood and the grout is kept sealed every few years it should last longer then you and I.


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## oh'mike (Sep 18, 2009)

Tile is used in pools and fountains--

Use powdered thinset (cement based) and you are good,even if it get wet every now and then---Mike---


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## Amateuralex (Mar 17, 2012)

OK I really appreciate the advice, thanks guys.


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## Maintenance 6 (Feb 26, 2008)

Mold needs an organic food source. There aren't any organics in ceramic tiles or cement or concrete floors.


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## Bonzai (Oct 29, 2010)

I would always advise to use some form of crack prevention membrane when laying tile on slab ... As a very minimum use a modified thinset that has a high elasticity content. The crack prevention membrane (or uncoupling membrane) however will also act as a waterproofing layer so that any moisture penetrating the slab from below does not get to the thinset and loosen the bond. Whether this is really necessary also depends in part on where you are located ... Not a lot of ground moisture in the Arizona desert for example ;-)


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## Amateuralex (Mar 17, 2012)

Bonzai said:


> I would always advise to use some form of crack prevention membrane when laying tile on slab ... As a very minimum use a modified thinset that has a high elasticity content. The crack prevention membrane (or uncoupling membrane) however will also act as a waterproofing layer so that any moisture penetrating the slab from below does not get to the thinset and loosen the bond. Whether this is really necessary also depends in part on where you are located ... Not a lot of ground moisture in the Arizona desert for example ;-)



That's very helpful advice. I am hoping to avoid using a crack prevention system, just to avoid the work. It's 650 square feet. There are a few very tiny cracks with no height difference and it's a 35 year old house. That makes me feel good about the cracks. I'll definitely use a modified thinset. I am planning on using 18X18 ceramic tiles, and will probably use this stuff (medium-bed thinset from reading other posts on this forum) from the Orange store: Custom Building Products 50 lb. Marble and Granite Fortified Premium Mortar.

The lower level is about 4 feet underground at the deepest. It has a walkout and low windows all around. It has a tile drain system and sump. It's flooded once in 30 years, but that's only because the previous owners abandoned the house, the utilities were shut off, and the sump pump lost power for 6 months. There's no evidence of water through the cinderblock walls or up through the slab.

How much of a pain is a crack prevention membrane to install on 650 square feet? In my situation, does it sound necessary?


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## Bonzai (Oct 29, 2010)

If you go with Ditra (Schluter product) then it is pricey and takes some time for that amount of space however you get what you pay for in terms of uncoupling ability. However you could use something like Mapei HPG or RedGard which are both roll on liquid membranes ... They look kind of like a tub of thick yogurt (without any fruit lumps) and it's just like painting to apply it. We use these a lot for exactly this sort of application as well as waterproofing shower walls. Would take a couple of coats and when dry you have a rubber membrane on the slab. You may need about 4 tubs for that space ... Here in BC I pay around $60 for the Mapei HPG .. RedGard is closer to $80 for the same size. The big saving is in the labour as so quick to apply ... It dries in about 90 mins. 
Whether you need it is hard to say ... It gives an extra level of protection. We guarantee our work so this is what we do to be comfortable giving that guarantee. Is it worth spending one more day and maybe $300 in relation to what you are already spending on the space ?


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## Amateuralex (Mar 17, 2012)

Huh OK very interesting. Something like Redguard seems very plausible and relatively easy. I'll definitely consider this, thanks again for the advice.


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## Bonzai (Oct 29, 2010)

Amateuralex said:


> Huh OK very interesting. Something like Redguard seems very plausible and relatively easy. I'll definitely consider this, thanks again for the advice.


It may well work without but as a contractor I need to give guarantees so I go the extra step. Minimum code does not require it but I am not a great believer in scraping by minimum code.


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## Amateuralex (Mar 17, 2012)

Bonzai said:


> It may well work without but as a contractor I need to give guarantees so I go the extra step. Minimum code does not require it but I am not a great believer in scraping by minimum code.


Understood, makes sense.


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## wkearney99 (Apr 8, 2009)

Man, a whole floor painted with Redguard... that's going to look like a slaughterhouse! I've used it behind bathroom tiles, interesting to hear someone using it for a whole floor.


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## Bonzai (Oct 29, 2010)

wkearney99 said:


> Man, a whole floor painted with Redguard... that's going to look like a slaughterhouse! I've used it behind bathroom tiles, interesting to hear someone using it for a whole floor.


The OP is going to tile on top of it ... Personally I would use the Mapei HPG as it is cheaper (here) and I find it goes further, plus it's a nice shade of baby blue as opposed to Barbie pink ;-)


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