A.Jim Hamrick
responds: There are two "subjective" tests
that can be used to check for the presence of
excessive moisture levels in a slab on
grade.
The simpler is the "Rubber Sheet/ Plastic Mat
Test." Using duct tape, carefully tape the edges of
a 2x2-foot piece of 4-mil poly to the slab for 72
hours. If you observe any moisture droplets or
surface color darkening of the slab, excessive
moisture is present.
A more definitive approach is the "Bond and
Moisture Test." Install a 3x3-foot piece of the
actual flooring material per specs, using the
proper adhesive. Seal the perimeter of the test
area tightly to the floor with duct tape and allow
it to cure for at least 72 hours. Remove the tape,
and pry the flooring from the slab. You have a
moisture problem if the tile comes up easily, the
adhesive appears damp and stringy, or the adhesive
releases from the concrete and stays on the
flooring material.
A more scientific test is the "Calcium Chloride
Test," where moisture migration rates are measured
using a petri dish covered by a plastic dome. If
this test is to be used, contact the flooring
manufacturer for the range of acceptable
values.
A good reference is the Armstrong Engineered
Installation System manual, available from the
Armstrong company (Armstrong Installation Products
Division, P.O. Box 3001, Lancaster, PA 17604;
717/397-0611).
Jim Hamrick is an architect in
York, Pa., and an instructor at Stevens State
School of Technology in Lancaster, Pa.