00CaliforniaZ28

iTrader: (11)

I used poly expanding foam from a spray can to fill in an unwanted opening in a piece of fiberglass, and now want to fiberglass over it, but after sanding the foam to the shape I wanted, the surface of the foam is porous and potmarked, and I dont feel comfortable trying to glass over it. Im guessing had I used the denser 2-part foam, this wouldnt have been a problem. I tried using some wall spackling in a small area, and it didnt seem to really help. Any ideas what I can use to smooth the foams surface? Thanks!

99345hp

bondo will work.

00CaliforniaZ28

iTrader: (11)

Was thinking that, but I guess for some reason was trying to outsmart myself and try something different.

I guess let me ask another question: The open area was pretty big, say 12"x10". What is the best way to cover that? The original plan was to fill with foam, then smooth the foam, and then glass over it. But I've been thinking, if I smooth out the area with body filler so its flush with the rest of the panel, and then glass several layers on top of that, then its gonna build up over the area and no longer be flush since the glass will be on top of something that was already smooth. But I dont trust using filler alone for that large of an area. How about fiberglass reinforced filler? I'm fairly new to bodywork, but have a lot of spare time so was trying to do some work/learning as I go along.

TA-Swede

iTrader: (4)

Never done bodywork on cars, but I've worked a lot with fiberglass in other applications.

For an area that big, I'd start out the way you did, but once you've bondoed the area, I'd paint it (to get it smooth), then paint it with release agent. After that, I'd use the area as a mold for making a negative out of it with fiberglass.

Once you have the negative, just do the same thing. Sand, bondo, paint, release-agent, and fiberglass it. Make sure you make the negative (and this final part) bigger than you actually need.

Now, trim the hole and the fill-panel you just made to the same shape. Fiberglass the part in place by applying strips of fiberglass from the background (4" overlap).
After that, I'm sure you can figure out how to fill in the seam between the part and the fill-panel.

If you complete this, I congratulate you. You've learned the basics for making your own fiberglass parts. It'll come in handy several times later on, I promise.

00CaliforniaZ28

iTrader: (11)

Thanks for the reply! I actually had thought about trying to make a negative mold, my only concern was that there is really limited access from the backside in order to glass the two pieces together. Id have to hack up the hood pretty good to be able to have access to fiberglass all the way around the joint from underneath.

Perhaps I can ground out the top enough to make a little lip, and then I have some 3M high strength adhesive I could maybe use to join the parts and fill in the seam. I guess Ill have to think about it some more, and it doesn't help that its a pretty curved surface I'm working with. Thanks again for the reply though, and I welcome any others with some advice!

99345hp

can you get your mold out? If you can then just build your foam to the correct shape just below flush. Then take the mold out and put on a skim coat of bondo. Paint then mold release the piece. Place it behind the panel to be repaired and grind the fiberglass thin next to the edge and feather it out. Then you can start laying your fiberglass matting and resin. Keep laying it down until it is flush with the outside surface. Then you can start finishing the piece.