TECHNICAL
BULLETIN 002
Topic
Radiant Heat Performance
PUBLICATION
DATE
Fall 2001 |
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Gypsum Underlayment Performance in Radiant
Heat Applications
LEVELROCK Brand
Floor Underlayments are specially formulated binders that are mixed by USG
licensed applicators with sand and water in the field to pour floor
underlayments. The specially formulated binders consist of gypsum, Portland
cement, and other additives. Since gypsum is the primary component of the
binders, it is commonly referred to as a "gypsum underlayment".
USG's
entry level product with its nominal compressive strength of 2500 psi comes in
two types - Regular and Radiant Heat. This technical bulletin explains the
differences between the two kinds of the nominal 2500-psi product and
emphasizes the importance of using the "Radiant Heat (RH)" binder for radiant
heat applications.
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| For radiant heat
applications, use LEVELROCK Brand Floor Underlayment RH (Radiant Heat) to
minimize calcination. |
Chemically, gypsum
is chemically calcium sulfate with two water molecules attached to it
(CaSO4. 2 H2O). When exposed to temperatures above 300
degrees F., the water molecules are removed to varying degree from the chemical
structure. This phenomenon is called "calcination". The speed with which
calcination occurs depends on the actual level of temperature and the duration
of exposure. However, even at temperatures between 150 to 300 degrees F., slow
removal of water molecules take place. The removal of water molecules results
in loss of strength and hardness of gypsum casts over time. Research conducted
by USG Corporation and others over the last 50 years has shown that there are
special additives that can be added to gypsum casts to dramatically slow down
and control the removal of the water molecules from the chemical structure,
especially in the temperature ranges of 150-200 deg F.
These special
additives that dramatically slow down the "calcination" of gypsum casts and the
resultant strength loss are present only in the "Radiant Heat" class of floor
underlayment binders. Thus, use of regular binders in radiant heat applications
is an invitation to failure of the floor system. Over time, the use of regular
binders in radiant heat applications will result in gradual loss of strength of
the floor and may lead to problems such as powdering and chalking. It also will
lead to poor heat transfer performance. USG Corporation only recommends the use
of LEVELROCK Brand Floor Underlayment-RH (Radiant Heat) in radiant heat
applications (either hydronic or electrical). Specifiers, contractors, and
licensed applicators need to make sure that the "Radiant Heat" formula is used
in Radiant Heat applications.
If you have specific questions on the
use of LEVELROCK Brand floor underlayments, please call 1-800-USG-4YOU and we
will be glad to help you in deciding if your application is suitable.
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