glassing over body filler?

[LKJR]

ok this is kind of offtopic I guess but relavent.

I'm building an icebox to go in the floor. The unit is insulated with rigid foam pieces I had laying around from someone's crazy packaging from shipping something I bought. So...

I did the inital layup on the foam with everything in place so I knew it would fit right. I started with resin then course fiber then some finer stuff but the last layer of finer stuff I tried doing it all with one piece and glassing in two phases.....well that didn't work out so well. next time just use seperat pieces no real reason to do it with one. But experiment it was.

I've gone back now and cut all the blisters out of it and sanded it down but I"ve got potholes as you might say where the blisters were.

So the question is if I come back and use plastic filler to smooth things out can I put a final coat of resin over that? or does it have to breath? I could use saw dust and resin but I'm using epoxy for this whole boat and it gets expensive fast. I'm going to paint this with a top coat paint btw. only exposure to water will be ice in the box and it will drain the water out the bottom.

[DavidJ]

Well the official word is if the icebox is made out of epoxy then no you can't use body filler. Epoxy resin contain unreacted acids that inhibit polyester based resins(which body fillers are) from curing. I would recommend epoxy thickened with cabosil if the "potholes" are less than a 1/4 inch thick and say half dollar sized. Any bigger and you should laminate in some fiberglass patches first and then fill over that if necessary.

That's the official word. Now you didn't hear this from me but polyester fillers often work fine over epoxy. I never use them if the fills need to be deeper than 1/8 inch, but most of the time they are great time savers. I don't mess around with different brands though. At my work we just find things that work and then stick with them. Too much money is wasted on trying out new wonder products. We use west 105 epoxy and polyfair(a marine fairing compound similar to body filler) all the time with no problems. Just make sure the epoxy is well cured, give it a good sand and spread it on there. I would definitely recommend doing a test one first because I have seen this not work. What happens then is there remains a soft uncured layer of filler between the cured filler and the cured epoxy. So go ahead and try it but don't blame me if it doesn't work.

[Tim B]

You can get stuff called micro-balloons which are tiny (foam?) particles which will turn normal epoxy (SP 113 or whatever) into a thick filler, but if you do it this way, for god's sake sand it before it sets off rock hard!!

If you've got deep holes then a little expanding foam will fill most of the hole (not structural though) and then a little filler and glass over the top works well. I used this trick recently to fair a center-board case into a hull (just to get rid of pools of water). If you can find yourself a model-aircraft/boat shop HobbyLobby or HobbyStores they should have some soft water-based type filler which will give a very smooth finish (usually in a white pot, looks like ready-mixed polyfiller) .it will absorb a bit of resin when you lap up the glass over the top, so it will set reasonably hard in the end. It is only useful for very thin finishing though.

You can get away with car body filler, but the trick is let it set off over-night before you epoxy over it. The polyester/epoxy bond is never the strongest, but if it's a finishing job then strength is rather secondary. What you want to do is keep the weight down.

Personally, I'd fair it with foam/model-aircraft filler, then give it one layer of very thin glass cloth, followed by a finishing layer of epoxy. when you're doing the glassing, it is easiest to do each face individually and over-lap up the sides a little way (2 inches or so).

Hope this helps,

Tim B.

Aircraft Spruce and specialty may still offer an extremely lite weight filler called "Super fill" if I remember correctly. Works well, easy to sand and bonds tenaciously.

[LKJR]

well guys I didnt get any responses in time so I went ahead and made some filler out of the resin and micro balloons I had. Just wanted to same some money and time!! the epoxy seems like it has to setup for a long time (practically overnight) before I can sand on it. (but I"m only at my shop for a few hours at a time.

thanks for the replies and most of all the experience related responses