To what degree is a heated slate floor-on-basement-slab vapor open?
LloydPDX
| Posted in Green Building Techniques on
We’re midway (I hope) through a basement remodel brought on by mold remediation and a thorough waterproofing project. Now considering replacing the existing small 6×8 bathroom slate floor with a mat-heated (such as “warmly yours” products) version. (Is this kind of installation considered vapor open?
Our home is in Portland, OR USA.
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Lloyd PDX,
Most common tile types are not vapor open, not sure what slate would come in at. The grout is certainly vapor open in that water splashed on the floor will make its way down. Presumably, a wet slab would migrate moisture up through grout as well. Not that you want a wet slab to work on.
It is not clear what form of water problems lead to your remodel so without that knowledge it is very hard to say much else beyond the floor heating wires I experimented with in a past kitchen did warm the floor pretty well at the closest allowed spacing.
The kitchen was a test bed in anticipation of a complete new build. I set the wire pattern in three zones to see how tile would spread the heat. Good thing I did, the heat did not spread across the tiles at all like I expected. At 2.5" between wires it was pretty easy to feel the bands of heat under foot. The tiles were 98 cent HD specials, but I believe the material density and behavior would be true of most materials.
I incurred two sensor failures and one thermostat failure in the five remaining years the kitchen survived. Fortunately, on advice gleaned here on GBA I had put in three sensors. Maybe the last one would have survived. There was a very pronounced disconnect between the thermostat and the floor warmth sensor. In order to keep the floor active and warm, it was necessary to set the thermostat very high. Even in our very drafty old kitchen it provided too much heat if we wanted warm feet.
I know you want a warm bath floor, so plan on a waiting a good bit to feel the heat or look into what is safe to use as a timed heat cycle. I am not sure if the wires can take sustained current. I do know that setting tile over the wires and staple contraptions was a royal PITA. The Schluter system or the film types of heating elements would deserve a very close review.
Per your description, peeling up a slate floor (even a small one) could be a real chore. If comes up easily that is a warning sign that the slab is going to fight you. Overall the vapor openess of a small area of the basement concerns me less than how much vapor is being pumped up across the rest of the basement slab. Do you have other flooring or carpeting in the same basement to describe before the remodeling? Are you sure the mold problem was from wall based issues and not wall and slab issues?