Non-Frost Resistant Slate in frost area - Is it possible?

mrlegoman · 10-23-2010, 10:09 PM

We are tiling our front porch (11'x18') with a pattern of 6x6, 12x12, and 24x24 slate from Home Depot. We have 3/4" plywood on 12" centers I think. I'm going to lay down 1/2$" backerboard and a layer of Ditra. The porch is covered, but the sides are open, so it will get wet and some snow.

We live near the southern part of Va and temps are already starting to dip near the 30's at night. I was planning on sealing the stone with Quikrete Natural Look Waterproofer:
http://www.quikretecoatings.com/quik...erproofer.html

We got the slate in and they are generically labeled "Premium Natural Stone - Gauged Classic".
On the 12x12 slate there is a big sticker "Non-Frost Resistant Slate".

So I'm starting to worry that I may be heading down the wrong path. I see people using slate all the time for outdoor projects.
Did I simply pick the wrong type of slate? Should I stop now and select another type?
With proper sealing, should I be ok?

JazMan · 10-23-2010, 11:10 PM

You've selected the wrong materials for outdoor use if there's a possibility for below freezing temps. Even some slates that are not labeled "non-frost resistant" may only resist for a number of cycles. After that you can vacuum the pieces.

You should find a real porcelain tile that claims an absorption of .05% or less. Plenty of slate looking porcelain tiles out there.

We always want two layers of plywood totaling 1 1/4" as a base when installing natural stone. The concrete backer does not add anything to the structure except height. Ditra is a good choice if all the other requirements are met. It would also be nice if you had a slopped substrate for water run off.

The other spec to keep in mind is the joists' deflection rating. Natural stone requires much stiffer joists (L720) than porcelain and the normal home construction norms. (L360). Let us know; the type and size of the joists, their condition, species and grade, double check the on-center-spacing, measure the span from support to support.

Sealing the installation will not make the installation waterproof, it'l just make it easier to maintain. Water will get in thru grout and hair line cracks.

Jaz

mrlegoman · 10-23-2010, 11:22 PM

Thanks for the quick reply Jaz. I'm heading to the house site tomorrow and I will double check all the dims of the support structure.

I'll also talk to the boss (wife) and see of she'll accept something other than a natural stone.

Will post what I find tomorrow. Thanks again.