Impregnated Open-Cell Foam Instead of Just Closed-Cell EVA Foam?
Impregnated, open-cell, foam is used as the backing for precompressed
sealants because it features very
low compression set.
Compression set is the permanent loss of the
ability to self-expand that results after a material is subject to normal
compression cycles. Compression set is made worse by simultaneous
exposure of certain materials to heat.
Closed-cell foams suffer on average
25% permanent compression set under movement and temperature cycles typical
in construction-related structural expansion joint applications.
The most common type of closed cell foam offered as an
expansion joint seal is Ethylene Vinyl Acetate or EVA. You may be
familiar with products that use the letters "EVA" as part of their name.
This is becasue that are made from ethylene vinyl acetate closed-cell foam.
Exploration of the suitability of EVA as the main component
of an expansion joint sealant is decades old. Attempts by EMSEAL more than 25 years ago, as well as repeated
more recent exploration using closed-cell EVA foam backings confirms that this approach does not offer
comparable alternative to
acrylic-impregnated, pre-compressed products for applications involving
movement typically experienced at structural expansion joints.
Despite this loss of active backpressure to compression-set, closed cell
backed materials are offered as inexpensive alternatives to the
impregnated, open-cell backed products.
Because the material is
not supplied precompressed, it must be force-compressed in the field and because compression-set further limits the
recovery, closed-cell based
hybrids should not be considered equals to impregnated foam sealants.
|Why not use lightweight, inexpensive
closed-cell EVA backing?
(EVA)-backed hybrid shown at
supplied size of
2-1/2" for compression into a 2" joint opening.
Permanent loss to compression set of 25% of
the movement capability of the product.
This means that in
extension to the claimed movement of +25% (when the structure cools),
this product would go into tension at the bondline and within the
fragile closed cell sructure of the EVA foam backing material.
This permanent compression set results after a single 3-hour
cycle with the material compressed to 1-1/2" and heated to 150-deg.F
(i.e. -25% of nominal size per movement claim at a very commonly
experienced summer substrate temperature).
Once again, your
feedback as to the conditions of performance used to validate our claims, or
challenges to facts presented are invited. Please send them to
email@example.com. Thank you.
For complete guide
specifications for EMSEAL products, please go the individual product pages
at our Product and