I did a hotcoat about a week ago and it is still tacky. It is not as tacky as a lam coat but it still clogs the sandpaper within a few strokes. I know I set it off pretty hot because it gelled as I was still brushing but that only left a few drag marks as I was almost finished anyway. The resin was a few months old so that could be it.
Is there anything I could do to get this hardened up? I was thinking another thin hotcoat but the board is already rather heavy and I would like to avoid this if I have to. If I have to do another hot coat is there a good way to get the first hotcoat off?
Look in the archives. There’s plenty of comment on this one. If your resin was old the wax probably settled. Just re-hotcoat with a “piss-coat” surfacing resin cut 10-15% with acetone, then sand. Anyway you do it it still requires a fresh hotcoat. McDing
Do as McDing advised, the thin overcoating will harden the one below. If you’re concerned with the weight, sand down to the weave using 80 grit and a slow speed. Next time measure your catalyst, add a little more if pigmenting.
you can’t harden resin once it has set. The chemical action just isn’t there. What you can do though is overcoat with a properly catalyzed hot coat, then proceed as usual.
What you need to analyze is why this happened in the first place. There are several causes, but you mentioned the probable cause already: overcatalyzing. The resin went off so fast, the wax didn’t have time to rise to the surface and seal it. Second, you were still brushing it when it went off, so your were “mixing” the wax back into the resin, again preventing it from rising to seal the surface.
Next time, don’t set it off so fast. Obviously, it produces a poor finish for several reasons, wastes catalyst, and overcatalyzing weakens the resin. Resin cures hardes at about 1 percent catalyst, which will give a 10 minute life here in Honolulu (plus or minus for local temperature, humidity, and several other variables).
There’s nothing wrong with a “hot coat” that doesn’t go off in five minutes. They are called hot coats because you want them to go off fast, so a lot of resin will stay on the board, particularly on the rails where it would otherwise drain off. This gives you a lot to work with and you can do a good job sanding. But really, if you haven’t squeegeed your lam too dry, a normal batch of lam resin plus surfacing agent will be all you need. Dump it on, spread it out, cross stroke once, long stroke once, and don’t to set it off so damn quick.
I think someone else already said this, but it has to do with the wax. If the wax isnt mixed well or if there isnt enough it will set up tacky. The main difference between lam and sand coat is the wax.
I’m pretty sure it was a combination of it being old resin with the wax not mixed through properly and my setting it off to hot. I didn’t mean to set it off that hot, hence I got the drag marks in it. I’m going out to try that wax paper trick right now. If it doesn’t work I guess that I will just have to eat it and do another hotcoat.
Try this- get some PVA and paint it on there and let it sit for a day. This works to harden up gel coat so it can be sanded. That is get coat is polyester with no wax in it so it should work for you . It works for me. PVA is poly vinel alcahol. It is used as a parting agent on new or funky molds as well as to get bummer batches to harden up. If you can find some one that is makeing molds for boats you can get dixe cup full and get it done. It is water souluble and can be painted with a cheapo brush. Fiber glass hawaii has it but you gotta get a gallon which will last for a few lifetimes. Let us know how ya do.
