|Q||On this project the Structural Engineer has specified a brand name epoxy or APPROVED EQUAL but the contractor wants to use a different brand – “the equal”. What constitutes an equivalent epoxy?
|A||2/07 – Response prepared by Lee Mattis, Division Manager for CEL Consulting and a registered engineer in California
Let’s talk about the different types of adhesives first. There are two primary types of adhesives: pure epoxies, which depend on the physical mixing of the two parts (resin and hardener) and vinyl esters and acrylics, which depend on a polymeric chemical reaction between two parts (resin and initiator). There are fast set and standard (slower) set versions of epoxies. The vinyl esters and acrylics typically gain strength quickly and can have load applied accordingly. Acrylics work well at low temperatures. Some products do not have good long term creep performance, which is an issue when constant loads are applied.
The application drives what is specified.
The chemical formulations provide the performance characteristics and they can vary greatly. So it’s not just a matter of load-carrying capacity when looking to determine an “equal” or “equivalent” epoxy. The application drives what is specified. In some cases it may not make any difference which product is used (e.g., a hold down inside a wall). In others it is critical (e.g., a suspended ceiling). Therefore the issue of “or equal” for adhesives is something that only the specifier (project engineer) who knows what is needed for the specific application, can answer.
It should also be noted that when a specification included on Approved (Building Department approved) plans includes an allowance of an “approved equal” or “approved equivalent” the responsible design professional must provide the Approval. Where the plans include a simple allowance of an “equal” or “equivalent” the responsible design professional should be requested to provide their approval for a proposed substitution based on the variable performance characteristics of the numerous epoxies available as discussed above.
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