Thought I was being clever using a heat gun to speed up glue drying on a spine...

I was working on a 16th century style binding replica last Saturday and decided to use my heat gun on low to hurry up the PVA on the spine. Well, I got distracted for maybe 45 seconds and ended up charring the leather right through the mull. Now I have a crisp black patch that looks like I dropped a cigarette on it. Has anyone else melted something they shouldn't have with a heat gun?

3 comments

3 Comments

thompson.nathan8d ago

Hang on real quick. PVA glue actually has a pretty LOW heat tolerance, so a heat gun on low is already pushing it past what the glue can handle. The heat probably softened the adhesive before it even had a chance to dry properly, and then the leather just took the brunt of it. You might have better luck just letting PVA dry naturally or using a fan on low to move air over it.

andrew_rodriguez8d ago

Honestly, that's a really good point I hadn't even thought about. So if the heat gun softened the glue too fast, would you say the best move is to just let PVA dry completely on its own, like overnight? I'm kinda wondering if a low fan would still mess with the glue's bond since it's just moving air around. Has anyone tried that with leather before and had it work out okay?

felixlee6d ago

Andrew actually brings up a good point about the fan, but I think the real question is did the heat gun mess up the glue's bond before the charring even happened? Because PVA is thermoplastic, so it softens when it gets warm and then hardens again when it cools. If you hit it with a heat gun, even on low, it might have softened that glue layer and let the spine move around just a tiny bit, creating weak spots where it re-dried. Ive seen that happen with book hinges where the glue never quite sets right after being heated too fast. So even if you avoid the leather damage, the actual structural bond could be compromised, which is way worse than a cosmetic burn in the long run. Did you test the joint strength on yours after it cooled down or just notice the black patch?