Bathroom Floor Waterproofing on Slab
2001 home in N GA area, CZ 3A/4A
Complete gut reno
Do I need to add waterproofing before installing tile on the slab in the bathrooms? The home has a plastic vapor barrier in the slab, but we have noticed some small amounts of moisture coming through when it rains really hard, so it likely is no longer as effective as it used to be. My contractor mentioned that adding a moisture barrier to the slab (whether it’s painted on, plastic, Schluter, etc.) could end up directing the moisture that’s seeping up from the slab towards the framing, so he’s hesitant to add any waterproofing. He said that installing the tile directly to the slab should allow it to “breathe” and dry in both directions. Thoughts?
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Vapor drive is a powerful force and most tiles aren't very permeable so you could end up with popped tiles. I would fix the source of the problem before adding new finishes. What is your exterior grade and drainage like? Do you have gutters?
We recently removed all of the overgrown shrubbery that was up against the house, and the exterior is about to be finished. So at the moment, it's just soil against the slab, and there aren't any gutters. We plan to grade the land so that it slopes away from the home, add gravel in the flower beds, and of course have the new gutters installed. We didn't notice the inward vapor drive until we removed the plants and gutters, so we are hoping that addressing those things will help significantly!
Bubbling this back up, as we are still making decisions about flooring. Is installing porcelain tile directly to the concrete slab an acceptable practice?
We are also considering LVP on top of DMX 2.0 for everywhere except the bathrooms.
Thoughts? Pros vs cons?
tjones,
You want a decoupling membrane to isolate the tile from the concrete below.
Does that apply to the whole home, or just the bathroom?
Any specific product recs?
tjones,
Anywhere there is tile on slab. I like Schluter's Ditra
Is the main purpose of the uncoupling membrane to prevent cracks in the tile/grout, or are there other reasons?
tjones,
https://www.schluter.ca/schluter-ca/en_CA/Membranes/Uncoupling-(DITRA)/Schluter%C2%AE-DITRA-&-DITRA-XL/p/DITRA
Thank you! What are your thoughts on the peel & stick version? Just as effective?
tjones,
I haven't tried it, but don't see why it wouldn't work well.
Is there any risk with trapping moisture if the slab's moisture barrier is no longer effective? Or are the "vents" in the ditra enough to help it dry? Would not sealing the seams or edges help with dryability?
tjones,
Just as with stem-walls, moisture isn't trapped in the concrete, it simply comes into equilibrium with the moisture around it. If the underside vapour-barrier is compromised, the Ditra becomes the primary one.
How about using ~1/8” wedi board for a bit of insulation and bring the tile up to hight with DMX2 and LVP. It would act as decoupling as well.
Malcolm, would that mean that any moisture that makes its way up the slab would be unable to dry if the ditra is blocking it from traveling any further? To me, if the ditra is the primary barrier, could that mean that moisture could be essentially pushed to other areas like the framing if it doesn't have a drying path? Thank you for your help - I have a hard time wrapping my head around building science.
tjones,
It's no different than if you had an effective sub-slab vapour-barrier. You don't want the concrete or ground underneath to dry up into the house. The is an inexhaustibe supply of moisture there. Blocking the movement of moisture doesn't sent it elsewhere, it stops it. That's really the definition of a vopour-barrier.
Thanks so much, Malcolm! On the subject of flooring, do you have any experience with a dimple mat like DMX 1-step for under LVP? If we go the LVP route, I don't want to install the LVP directly to the slab since there are areas where more moisture comes up. Any suggestions here?