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National City  CA  91950
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Resolite Products




Corrosion Resistance

Since the 1950's, fire retardant polyester resins have been used for building panels in corrosive atmospheres. There are many resin systems available having varying degrees of corrosion resistance. Based on required characteristics and the intended use as an exterior FRP siding or roofing panel, Resolite established guidelines to select the optimal resin system.

First, it had to be flame resistant and able to meet Class 1 flame spread ratings. Second, it had to perform in all types of severe weather conditions. And third, it had to be resistant to a host of various chemical and corrosive elements. These criteria must be satisfied while maintaining an inherent toughness and resiliency and an ability to meet the stringent load/span requirements of the major building codes. Resolite's high quality isophthalic halogenated polyester resin system is the ideal solution.

Isophthalic polyester resins have some major advantages when compared to orthophthalic polyester resins. While orthophthalics offer good corrosion resistance, isophthalics provide higher heat resistance, greater retention of physical properties, better chemical resistance, and greater composite strength when bonded to fiberglass reinforcement. In laboratory tests, a fiberglass reinforced isophthalic polyester resin panel showed 10% higher flexural and 20% higher tensile properties than a comparable panel using orthophthalic polyester resin.

Vinyl ester resins are another possible choice. They have good corrosion resistant qualities, in some environments better than polyester resins, and may perform satisfactory at slightly higher temperatures. Fire rated vinyl ester resin systems, however, have a major drawback; they have poor resistance to UV and will weather very quickly. Vinyl ester resin is not recommended for use as an exterior wall or roof panel since severe color changes and UV degradation will occur.


The first fire retardant panels had good corrosion resistance in a host of harsh environments. However, they had very poor weather resistance and soon yellowed from ultraviolet attack. Fibers were also becoming exposed in three to five years. Coatings and films were tried but none of these proved to be a long term solution.

Resolite soon realized that weathering, mainly UV degradation, was a major factor that impacted the quality and long term performance of its products. For decades, Resolite has been in the forefront of providing solutions to this difficult problem. We were one of the first FRP producers to utilize SFTS (South Florida Testing Service), an internationally recognized environmental testing company, to evaluate long term outdoor performance. In addition, Resolite has had its own outdoor weather testing program for over 50 years.

Resolite's Research and Development Staff utilizes a Xenon-Arc Weatherometer. This device provides comparable natural outdoor weathering correlation at an accelerated rate. Resolite is able to evaluate the latest resins, pigments, reinforcements and additives in as little as 6 months instead of the standard 3 years required by traditional outdoor test methods.

The Superior Solution

Over 50 years of FRP evaluation and testing has led Resolite to the fire retardant isophthalic polyester resin system currently utilized. This system with neopentyl glycol, acrylic modification and UV stabilizers provides the best combination of performance characteristics. All Resolite fire-rated products, including FS25A, CRFS25A, Tred-Safe and RFM, utilize this superior polyester resin system. Coupled with a standard embossed resin rich surface, Resolite FRP panels provide the utmost in long term corrosion resistance and weatherability.



To further enhance panel corrosion and weathering performance, a C/W Barrier is incorporated by Resolite. C/W Barrier is a protective layer that is fused into the resin/fiberglass matrix to give the panel even greater protection against degradation. C/W Barrier is available as a standard on many Resolite FRP panels and as an option on others. Consult product descriptions or contact Resolite Customer Service for availability.

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