Sprayable foam

[GasSavers_Ryland]

I have used this kind of foam alot in houses, and a little in building molds, and so on, you can normaly get it about 3 inches thick befor it gets to thick to cure, if you have an inclosed mold then yes, it will take much much longer, as much as a month or more if it's a compleatly inclosed mold, open top like a paint pan should cure in a matter of a few hours, to a day depending on the foam you get.
if you want to do an inclosed mold, get the two part foam, it comes in two tanks, and can be sparyed as thick as you want, the two parts react with each other and cure fully, it's commenly used in houses, the kind of stuff they would use to spray all of your wall cavitys full, only you can get it in smaller quanitys, altho I think for the two part stuff the cheapest set up is around $50, but I haven't personaly bought one, so I might be wrong.
another thing to think about is regular fiberglass, I recently made a fiberglass mold of a metal tractor seat, so that I could make copies for putting on recombent bicycles, useing foam as a core in a piece made from fiberglass works really well.

[VetteOwner]

patches holes quite nicely:

[MetroMPG]

Nice!

[Bill in Houston]

So here's another thought I had about the foam. If you can build a prototype out of something easy to work with, you can use this foam to make a mold to mold a more durable final piece. I know that didn't make any sense. I'll use an example.

Say you want some fiberglass wheel skirts. You built prototype wheel skirts out of something easy to work with, like, uhh, floral foam or cardboard or paper mache or whatever. Silly putty, whatever. Then, you cover the prototype with foil or plastic wrap. Then you spray on the foam. While it's goopy you put in some small pieces of wood or plastic or whatever to make it stiffer. Once the foam sets, you remove it from the prototype piece.

Now, you have a really good start on a mold. You fill in the wrinkles, sand it nice and smooth, seal it with something, sand nice and smooth again, and wax it up with some paste wax or whatever you want to use as mold release.

Then, you spray/paint in your gelcoat if you want, and then lay up the fiberglass like you normally would. Keep building until you get to the desired thickness, pop off the mold and voila, your nice pretty fiberglass fender skirt. And maybe you can use the mold again to make a skirt for your buddy with the same kind of car...

[trebuchet03]

Originally Posted by Bill in Houston

So here's another thought I had about the foam. If you can build a prototype out of something easy to work with, you can use this foam to make a mold to mold a more durable final piece. I know that didn't make any sense. I'll use an example.

Say you want some fiberglass wheel skirts. You built prototype wheel skirts out of something easy to work with, like, uhh, floral foam or cardboard or paper mache or whatever. Silly putty, whatever. Then, you cover the prototype with foil or plastic wrap. Then you spray on the foam. While it's goopy you put in some small pieces of wood or plastic or whatever to make it stiffer. Once the foam sets, you remove it from the prototype piece.

Now, you have a really good start on a mold. You fill in the wrinkles, sand it nice and smooth, seal it with something, sand nice and smooth again, and wax it up with some paste wax or whatever you want to use as mold release.

Then, you spray/paint in your gelcoat if you want, and then lay up the fiberglass like you normally would. Keep building until you get to the desired thickness, pop off the mold and voila, your nice pretty fiberglass fender skirt. And maybe you can use the mold again to make a skirt for your buddy with the same kind of car...

That's almost EXACTLY how we made our HPV fairing.... Bondo makes a great filler/fixer for any imperfections in your foam cast

Instead of making a second one from your foam negative - which is really a tool... Make a better tool with fiberglass off of your first part. Unless you just want to make one or two more. But if you're going to make 5-10+ a more permanent tool will make a stable platform to work from (plus it can be vacuum bagged)

[ArtFox]

1) Which plastic sheeting or wraps will protect the body paint when building up a clump of spray foam for wheel skirts and such?

2) Has anybody combined polystyrene (pink/blue) or urathane home insulation boards (foil backing peeled off) and spray foam to build up contours? Does the spray-on melt the polystyrene?

[JanGeo]

stick with the yellow urethan foam because the bondo will attack the polystyrene Probably! but not the urethane and it should also be used with urethane glue i.e. Elmers makes it in various bottle sizes (Home Depot) and if you hit it with steam or hot water it really foams up fast and is a lot harder than the insulating foam and can be used to bond it together. Urethane will not stick to Saran wrap and some plastic shopping bags too.

[bowtieguy]

i used the great stuff brand from home depot to make a grill block. after applying black paint, it's not even noticable with the exception of very near viewing.

[ArtFox]

Thanks for the advice.

I only have the "minimal expansion" foam around the house. I did not want to distort some window frames I was insulating. Must get the max expanding stuff!

I have rasps, carving tools and dust masks already...

[palemelanesian]

Acetone will remove it from your hands, while it's still wet. It says so right on the can, and I've verified that it works. Have some on hand! Once it's dried, though, it's too late.