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The ease of application and huge yield from a single can of pro-style foam is reason enough to use a gun rather than a straw, but like many other carpenters, I’ve long been frustrated with the reliability of my foam guns. I’ve tried a lot of brands, and sometimes had them quit working after only a few weeks. But after several conversations with industry insiders, I learned that the problem wasn’t the gun—it was me. With a better understanding of how the gun works, and what can cause it to fail, I’ve learned the secrets to keeping this tool working well for years. Moisture is the key The first step is to understand foam chemistry. Canned foam has three main ingredients: polyurethane resin, propellant, and fire retardant. Some foams have additional ingredients for specific purposes, like capsaicin for pest control or dye to differentiate the color of, say, foam construction adhesives vs. foam for filling holes. No matter what type of foam you’re using, the chemistry behind how it works is the same. The can keeps the propellant in a liquid state, but when you pull the gun’s trigger, the pressurized propellant is released as a gas, pushing the liquid…
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