Thermal mass floor tile conduction
Newbie, DIYer, trying to finish a direct gain passive solar residence by installing quarry tile with unknown (at the moment) thinset/mortar/adhesive over a very dense, 4″ concrete slab that has a machine-steel-troweled, nonabsorbent, slightly rough (but not fine broomed) profile. I’ve got two issues to solve sequentially;
1.) efficient thermal conductivity of the whole thermal mass sandwich (ie tile to thinset to slab) is in question because there appears to be no testing of the various thinset/mortar/adhesive conductivities, only contradictory opinions as to such.
One passive author states: a slab’s coverings (ie quarry tile in my case) and its thinset/mortar/adhesive that are poor conductors of thermal heat will clearly interfere with the flow of heat in and out of the heat storage mass. In extreme cases the heat storage material can be rendered useless. The thermal conductivity of both a tile and its thinset/mortar/adhesive should be at least as high as that of the slab. Tile should be bonded with no-air-pocket workmanship to assure a good thermal connection or continuity to the underlying slab…
The problem arises because the types of thinset/mortar/adhesive can include latex-modified Portland cement, acrylic-modified Portland cement, emulsified epoxy Portland cement, 100% epoxy mortar, 100% epoxy adhesive, furan, organic adhesive, and standard Portland cement thinset. Each has a different thermal conduction coefficient, with latexes and acrylics being suspiciously low (see this thermal conductivity chart for specific materials like acrylics, epoxy, dense concrete, cement mortar, rubber (latex is often called synthetic rubber?), porceline etc @ engineeringtoolbox.com/thermal-conductivity-of-selected-materials, but I can’t figure out how to use the formula to compute each approximate conductivity. ?
Other consultants say: the thinset/mortar/adhesive type doesn’t matter, none of them will interfere with your efficient conductivity.
Or others yet: definitely stay away from organic adhesive and latex-modified.
The National Renewable Energy Lab and the Dept of Energy’s office of Energy Efficiency both have no info re my question.
Both the concrete slab and quarry tile components of the thermal mass sandwich are well known to have acceptable conductivities.
2.) A better bond than standard Portland cement thinset (psst–it, naturally, has acceptable conductivity) is recommended by concrete technicians because this is a ‘cold joint’ application and not an ideal fine-broomed surface profile on the slab. They say that an epoxy adhesive would be an excellent choice if scarification of the surface is not an option for some reason (it isn’t an incredibly messy option!) and if epoxy adhesive can pass the conduction test (some say at least 10 BTU/hr-ft2-degree F) at its 1/16th” application thickness (only 1/16th” because standard Portland cement thinset can be applied over it if mortar sand is broadcast onto the wet epoxy to create excellent ‘tooth’ after curing)
Unimportant details: slab is well insulated from ground and perimeter stem wall foundation with 2″ extruded polystyrene and moisture proof with a tight vapor barrier. The gorgeous Sun-Glo quarry tile has already been purchased for the 700 square feet interior and I really want to use it if I can avoid slipping into stupid mode. The glass-to-thermal-mass ratio has been carefully calculated and built, control joints sawed appropriately.
Any furtive conductivity tests, quasi-engineer inputs, and general advice commentary would all be extremely welcome.
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