Using Brass Strips with Thin Set Epoxy Terrazzo
From the designer’s point of view, the use of brass strips is extremely important, because it gives them greater flexibility and design creativity. Brass strips have been and are still used as a strong and important design element in the aesthetics of cement and epoxy terrazzo.
Back ground: Several years ago we were asked by our key terrazzo contractors to formulate a thin set epoxy terrazzo matrix that could be used with brass strips, without fear of immediate or future amine induced staining. Their desire, as well as the desire of the design and specification community, was to have an epoxy matrix that would not chemically react with the copper in the brass strips.
Pre-coated brass strips: The practice of pre—coating the strips, with a protective coating, had been determined to be a non—viable option, because of numerous field failures. In a large number of cases, the coating on the pre— coated strips failed to protect the brass strip from coming in contract with the aggressive epoxy hardeners. This was because the coating was damaged or removed when the strip was cut or bent. The pre-coating was also removed during grinding of the floor and then it would be exposed directly to the epoxy, and/or worn off later through use.
Chemical attack: Chemical attack of the copper in brass strips by the corrosive hardeners had lead to many field problems, resulting in an unsightly blue staining of the marble and epoxy matrix. The design community and the contractors strongly objected to the staining for aesthetic reasons. Finally, even if the brass strip survived the grinding process without staining, it would subsequently be exposed directly to the corrosive epoxy hardeners when the system was grouted and finished.
Solution: General Polymers solved this problem and introduced a brass strip compatible epoxy terrazzo matrix. The formulation, now over twenty years old, does not react chemically with the copper in the brass. This scientific break through resulted in a product that met the design communities and contractors needs, alike.
Why it works: One of the reason it works, is because General Polymers 3520 epoxy terrazzo matrix formula does a superior job of “tying up the amines (hardener) in the chemical complex”. The absence of free amines means that the hardener will not react with the copper in the brass strips. This is not the case with competitive products.
Competitive Product Staining: The brass strip color change and leaching (resulting in staining the marble and epoxy matrix in competitive systems), is caused by a chemical reaction between the amines in the hardener and the copper in the brass strips. The copper is chemically attacked by uncured or free amines from the curing agent in the epoxy systems. If the formulation is not especially tailored for this application and mixed exactly right, the brass strips will be attacked chemically by amines present in the epoxy hardener, prior to cure and after cure if the amines are not tied up in formula. Therefore, if the contractor errors even slightly with the mix ratio, staining will result. General Polymers has introduced a product to help solve this problem. FT 837 Brass Blue Stain Remover is applied to a stained epoxy and will chemically react with the metal to remove the stain from the epoxy terrazzo.
Weakened Epoxy Matrix: Excessive bluing of the marble and epoxy matrix may also be an indicator of product miss mixing. Several products on the market are extremely mix ratio sensitive. Meaning, if the ratio (“A” to “B’) is slightly off, the matrix will not gain its reported physical and mechanical properties. An amine rich system (excess hardener) accelerates the staining and may be an indicator of more serious problems to come. Miss mixed material, leading to an incomplete cure may also affect the terrazzo’s appearance in other ways, such as inconsistent color, inability to clean, easily worn away, etc.
A hardener-starved matrix attributable to miss proportioning is considered to be “non—durable”. Non—durable terrazzo usually deteriorates faster at the strip or joint lines. The effect of a weaker leading edge has a severe long-term durability consequence that will not be immediately observable.
General Polymers system is mix ratio “tolerant”, therefore you do not have to worry about staining, even if a slight mixing error does occurs. (General Polymers insists that ratio mixed be correct, because other physical properties will be affected, even if staining does not occur.) General Polymers 3520 thin set epoxy terrazzo resin and hardener was designed to be user friendly, with a mix ratio of 4:1. Placing thin set terrazzo floors is an art, not a science. It is a difficult art, requiring expert installers. Let us consider the advantage of General Polymers 3520 4:1 mix ratio vs. the 10:1 mix ratios regarding the subject of field miss proportioning errors, examples:
A 4:1 ratio means the system is 80% resin and 20% hardener. A 10:1 ratio means the system is 91% resin and 9% hardener. The 10:1 mix product has a B side which contains 2.5 times the relative amount of amine functionality as compared with the 4:1 product. The same volume variation in mixing the b-side of both products results in a 2.5 times excess amine relative to the 4:1 ratio product. Most of the 10:1 ratio materials require absolute proportioning, because if their ratio is off, even slightly, the excess amine will attack the brass, if this occurs the supplier simply blames the terrazzo contractor.
Epoxy is inert: Some manufacturers will argue that cured epoxy systems are inert (neutral pH) after cure. That statement at face value is true, however if uncured amines are free to migrate out of the system, then the system is not inert. Cured epoxy is often thought of as inert, but unless the reaction is complete, free amines will exist. These free amines are ‘available’ to attack the copper in the brass strips for the life of the system or as long as they are available to migrate out of the system. This helps to explain the long term blue staining that may appear.