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. 

Other than EMSEAL, there is only one US-based manufacturer of precompressed foam sealants.  This other manufacturer while offering its own branded products also private-labels their isobutylene-and-wax-base saturated products to all (nine (9) at last count) other US-based expansion joint manufacturers who claim these products as their own.

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 and reveal the shortcomings of both wax and asphalt-based technology predecessors. 

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

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

EMSEAL's own asphalt-compound impregnations as well as the wax-saturations of other alternatives are not capable of the same performance as acrylic-based products.

Should you encounter products being offered with the same performance claims, we would encourage that these claims be tested and certified to the same performance conditions described in this bulletin.

We believe these performance conditions to 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, fills the foam cells completely 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.

Movement, Recovery, and Trade-Offs:
Because a large movement capability combined with high temperature stability and low temperature flexibility are the overarching performance requirements in high performance (100% total movement capable) sealants, it was realized by EMSEAL that it would not be possible (as in its 50% movement capable COLORSEAL product) to achieve watertightness in the foam backing while being able to accommodate the full range of movement across achievable temperature conditions.   

For this reason EMSEAL has never claimed that the foam backing is performing a waterproofing function in the 100% movement-capable SEISMIC COLORSEAL product for example.  Instead, the acrylic-impregnated foam provides:
a) the support for the watertight silicone bellows;
b) thermal insulation in the joint it is sealing;
c) a non-invasive anchoring mechanism;
d) the dampening mechanism by which the material can be precompressed and practically inserted into the joint rather than forced into the joint.

Claims of 100% movement capability AND watertightness in the foam backing AS WELL AS high temperature stability in combination with compression should be treated skeptically.

SEISMIC COLORSEAL is a hybrid silicone-and-precompressed-impregnated foam sealant.  The silicone component is a factory-applied bellows on the weathering face.  The benchmark performance claims are:

1.  Movement Capability:  100% of nominal material size.  More explicitly this 100% is comprised of  -50% compression AND +50% extension from nominal size. This means, for example, that 2" nominal material has the capability to be compressed to 1-inch and extend to 3-inches during the thermal cycling of a substrate.

2.  Application and Substrate Suitability: These materials are offered for use in applications involving porous substrates such as concrete, brick, stone, etc. and non-porous substrates such as the metals used in curtain walls and metal panels.

3.  Active Backpressure: Precompressed sealants are claimed to actively recover as the result of the stored-strain energy of compression in the foam backing.

Typical descriptions include back-pressure inherent in the elastic open-cell foam backing.”, and “works under its own constant internal pressure”.

5.  Temperature Stability and Resistance to Bleeding:  High temperature stability of 185°F (85°C) is typical. 

By “stability” it is assumed that the chemical emulsion is stable or will not melt, soften, or bleed from the foam matrix in which it is retained.   "Bleed” is assumed to mean the loss of the chemical emulsion from the foam matrix into or onto adjacent substrates or building materials.

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

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, temperatures of 180o F (82o C), and 185o F (85oC) were 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 formulated for as much as one-third the cost of 100% acrylic dispersions, by virtue of their inability to perform under conditions reasonably determined to simulate real life conditions they should not be considered viable alternatives to higher performing 100% acrylic-impregnated 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. 

Regardless, manufacturers should be held accountable to prove their product performance to the claims they make in data sheets.

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:

All products to be certified in writing to be free, according to independent testing using FTIR and DSC,  in composition of any waxes or asphalts, wax compounds or asphalt compounds.  All substitute candidates shall be certified in writing to be:
a) capable of withstanding a minimum of 185°F (85°C) for 3 hours while compressed down to the minimum of movement capability dimension of the basis of design product  without evidence of any bleeding of impregnation medium from the material; and b) that the same material after the heat stability test, and after cooling to room temperature 68°F (20°C), will self-expand to the maximum of movement capability claimed within 24 hours.

Independent Lab Certification--Wax Free
Fournier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) testing conducted by an independent laboratory is a simple way to determine if the pre compressed foam sealant being considered contains wax that might affect performance.

All of EMSEAL's foam sealants are certified by independent laboratory to be free of wax or wax compounds. Click Here to access the test reports.  Demand the same of substitutes.

Still Skeptical? 
Request samples of any of the following acrylic-impregnated products from EMSEAL and request the 'equals' from others. 

Open, handle, and even run these simples tests to compare for yourself.  We are confident you will agree that it is possible to offer the best possible performance while delivering the best value, custom made for your job, at lead times that respect your project schedule:  SEISMIC COLORSEAL, COLORSEAL, DSM SYSTEM, BACKERSEAL, SJS SYSTEM, HORIZONTAL COLORSEAL.

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.


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: April 26, 2015

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