[VAC] Re: Balsa core flooring

[Dr. Gerald N. Johnson, electrical engineer]

I believe that the modern radiant floor heating is based on 120�F water,
not 180 and that the PEX is not rated for continuous use at 180.
Certainly that may be a warm temperature for the foam.

Why not Formica for the top skin? It could be a maple block pattern, or
green marble or many others. Its strong, can be the finished surface and
stands heat and other abuse.

If the foam was the same thickness as the tubing diameter, it would be
more productive to rip the foam into planks with a table saw than to
route it for tubing. The end turn regions would need to be routed.

Thinking about materials that are relatively easy to find, Menards
carries a fiberglass laminate panel for about $24 a 4x8 sheet. Most
every building store carries 1/2, 3/4, and thicker Dow blue board. Bead
board is not suitable. The only rub I know of for Formica (or
Wilsonarte) is that its sheets tend to be only 30" wide.

The adhesive of choice is probably water based contact cement, I know it
sticks dow foam well. There are probably some epoxies or polyester
resins that would work well. Solvent based contact cement will not work
with the foam, it disintegrates the foam on contact before the contact
cement can dry.

The lower skin needs to be a material strong in tension. Aluminum sheet
would work if its glued well. Its a bit harder to glue than wood or
scrap masonite.

Its a bit hard to insert tubing into a factory made panel though factory
panels can be inspiration for home made panels.

An alternative assembly might involve foaming after assembly. E.g.
spreading the tubing around the bottom sheet, then dropping on a top
sheet onto spacers with enough through fasteners to withstand the
pressure of the foam and some holes in one face or the other to allow
both squirting in foam and pressure relief. The through fasteners could
be removed after the foam had set and those holes filled with foam too.
Or the assembly could be held between two flat platen plates (might be
braced panels like concrete basement wall forms) and the foam squirted
in. This way the tubing would be anchored more tightly and would release
its heat a bit better than when kind of loose in rigid foam.

There are far more solutions that problem.

The insulation in the middle makes the foam with double aluminum facing
poor for putting the radiant tubing on the bottom of the assembly.
Aluminum conducts heat to the sides better than the insulation conducts
it through.

Aluminum as a top sheet on a home made panel would serve well to spread
the heat and to make a uniform surface. I'd consider a break in the
aluminum skin at the cabinets and the cabinets and not put heat plumbing
under those because they don't need warming, but the occupants do and
can only feel the heat that's not covered by cabinets. I'd put a thermal
break in the aluminum skin so the aluminum didn't conduct heat there
either.

I still think Masonite may be the optimum upper surface.

Gerald J.



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