Expansion Joints and Pre-Compressed Sealants



Benchmarks of Performance for High-Movement Acrylic-Impregnated, Precompressed, Foam Sealants When Considering Substitutions

EMSEAL has set the standard for precompressed foam sealants. 

This bulletin describes why the performance of EMSEAL's 100% acrylic impregnated precompressed foam sealant is different and unique.  It also offers simple testing procedures that validate these claims.

UPDATE: In recent years, and with advancements in hydrophobic chemistry, it has been shown that when carefully formulated, precompressed sealants can be produced with wax or asphalt as a component and not bleed at the extremes of movement claimed. Regardless of the impregnation formulation, it remains prudent for specifiers to require that precompressed sealants be proved, by testing, to ensure that the products specified will not bleed-out their impregnation when compressed to movement claimed and at temperatures known in the field to induce that compression.

The primary drivers of the performance of EMSEAL's precompressed sealants are:

1) The incorporation of a 100% acrylic chemical emulsion into a high-grade open-cell polyurethane foam, and the use of 'impregnation' instead of 'saturation' in the relationship of these component materials.

Specifiers should require the claims of precompressed foam sealant manufacturers be tested and certified to the same performance conditions described in this bulletin.

We believe these performance conditions accurately reflect those expected to be experienced, or reflect the designers expectations of performance, in applications for which the materials are being specified and installed. 

The following photographs validate the performance claims of acrylic-impregnated, precompressed sealants by comparing their claimed performance to the claimed performance of a wax-saturated alternative under conditions simulating real-life application demands.


Figure 1: Acrylic-Impregnated Foam

2-inch nominal acrylic-impregnated foam sealant compressed to 1-inch (-50% of movement claim),

heated to claimed high-temp resistance of 185oF for 3-hours (to simulate mid-summer, Southern exposure on a dark metal substrate).

1) The material compresses easily with acceptable force (11.32 psi) to the minimum of published movement.

2) No bleeding (expulsion, melting, or leaching) of acrylic impregnation occurs


Figure 2: Wax-Saturated Foam

2-inch nominal wax-saturated foam sealant compressed to 1-inch (-50% of movement claim),

heated to 185oF for 3-hours (to simulate mid-summer, Southern exposure on a dark metal substrate).

1) The material compresses with great difficulty requiring 35 psi force to move the foam to the minimum of published movement.

2) Bleeding (expulsion, melting, or leaching) of part of the wax saturate occurs.

A precompressed foam sealant relies for performance on a careful balance between the properties of its cellular foam component and its chemical emulsion component.

The chemical emulsion fills (in the case of saturation) or coats (in the case of impregnation) the cells of the foam.  The foam in turn provides the elastic memory that ensures an inherent active backpressure.  The amount of emulsion put into the foam affects the degree to which the mechanical back-pressure of the foam is dampened or deliberately restrained. 

Some dampening is essential to slow the expansion rate of the foam in order that the product can be practically installed into a pre-constructed joint opening.  Too much dampening can negatively affect the product's ability to expand as the joint opens when temperature drops.

Impregnation vs. Saturation:
Two philosophies have been employed in the production of precompressed foam sealants--impregnation and saturation. 

Impregnation is the process of using a controlled amount of emulsion distributed over the cell walls of the foam.   This measured coating is designed to avoid choking the foam and over-dampening it's spring-like elastic memory.  To achieve watertightness in the foam itself requires the use of an amount of impregnated foam that when compressed achieves a density impermeable to water.

Saturation, by contrast, substantially fills the foam cells and relies on less foam but a greater amount of chemical emulsion to achieve a seal.  This approach has worked historically in some markets where climate and design practice limits the movement range to which the product will be subjected. 

Hybrid Precompressed Sealants:
In response to the need primarily in North America for materials with higher movement range, as well as with market demands for colored seals, hybrid sealants were introduced by EMSEAL into the market in the early 1980's. 

The hybridization involved incorporating the dampened-spring feature of impregnated, precompressed foam sealants with a factory cured silicone liquid sealant in the form of a tensionless bellows. 

Asphalt, Wax, Acrylic--The Evolution:
Historically, the families from which chemical emulsions have derived are asphalt, wax, and acrylic.  The original invention in the 1950's was based on bitumen or asphalt.  The patent for this invention was circumvented in Europe through the use of a paraffin wax compound. 

Both wax and asphalt suffer similar shortcomings--low temperature brittleness and high temperature instability. 

Recognizing the ability of acrylics to extend the low-temperature flexibility of asphalt as well as to simultaneously improve high temperature stability, EMSEAL evolved its asphalt impregnations to incorporate an acrylic component.  This in turn lead towards the development of first-generation 100% acrylic impregnations and ultimately to the latest in the evolution of precompressed foam sealant impregnation--microcell-modified, hydrophobic acrylic impregnations. Even more recently, advances in super-hydrophobic chemistry, has provided further enchancements in impregnation chemistry as regards hydrophobosity, or the effect of repelling water.

Given that movement and temperature are related, it is reasonable to test the related claims in unison. 

Take, for example, a product claiming -50% and +50% (total 100% of nominal size) movement capability. Given that if specified and installed into a condition that will utilize the full movement claim of the material, it is reasonable to expect that the products can be compressed down 50% from their nominal size and that this condition will occur during achievable high temperatures on a building. 

Actual substrate temperatures on dark-colored substrates like bronze or black curtainwall mullions, on a Southerly exposure, during the peak mid-day hours, in summer, are regularly recorded at around 180o F (82o C).  For purposes of this testing, then, temperatures of 180o F (82o C), and 185o F (85oC) should be used.

Given that these products claim the ability to follow joint opening movement through their inherent backpressure, and that if specified and installed into a condition that will utilize the full movement claim of the material, it is reasonable to expect the material to recover unassisted from the compressed state achieved at the claimed high temperature stability point to the maximum of its claimed movement range.


1)  Six-inch long pieces of 2-inch (50mm) nominal material are removed from their shrink-wrap and hardboard packaging, and any mounting-adhesive release liners are removed.

2)  The samples are installed between the faces of identical, aluminum, clamping jigs.

3)  By tightening the bolts in the clamping jigs, the samples are compressed down to 1” (the -50% movement claim.  This dimension would be achieved in actual applications during the heat of the summer as joints close due to the expansion of adjacent structural materials).

4)  The samples are placed on a metal baking sheet, in a scientific oven, tilted at an angle of 30 degrees.

5)  The samples are then baked at 185-deg.F (85-deg.C) for 3 hours.  (This temperature chosen to simulate a south-facing, summer season, mid-day exposure on a dark-colored, metal substrate like a window mullion).

6)  After 3 hours, the oven door is opened and the samples observed for signs of instability of the impregnation, bleeding, and/or any change in the material.  If bleeding has occurred, the test is failed and discontiued.

7)  The samples are allowed to cool to room temperature. 

8)  The clamping jig bolts are loosened to allow the samples to recover. The recovery of the material over the next 3-24 hours observed.

As illustrated in the photographs above, under conditions achievable in field applications, the the acrylic-impregnated SEISMIC COLORSEAL material shows no evidence at all of bleeding, leaching, or melting of acrylic impregnation either onto the substrates or out of the foam.

As the temperature slowly drops to room temperature the substrates are moved slowly apart. The acrylic-impregnated SEISMIC COLORSEAL begins immediately to self-expand and the silicone bellows achieves expansion to 3-inches (75mm) within 3 hours while the acrylic impregnated foam backing expands to beyond 3-inches (75mm).

While wax-compounds, like asphalt-compounds, can be carefully formulated to perform as offered, they must be tested to perform under conditions reasonably determined to simulate real life conditions or they should not be considered viable alternatives to proven alternatives.

While there remains a place in the market for low-movement, moderate-temperature applications for asphalt or wax-based products, many of today's construction environments and applications call for higher performance. 

Consequently, should you be specifying an impregnated foam sealant product we suggest you require proof of movement capability and temperature stability in combination, and incorporate the following language in your specifications:

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 content@emseal.com.  Thank you.

For complete guide specifications for EMSEAL products, please go the individual product pages at our Product and Application Index.



Update: March 2016


EMSEAL JOINT SYSTEMS LTD. 25 Bridle Lane, Westborough, MA 01581
EMSEAL LLC. 120 Carrier Drive, Toronto, ON M9W 5R1



1-800-526-8365 -- 508-836-0280 --  techinfo@emseal.com -- Fax: 508-836-0281

Last Modified: March 2016

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