I have to make a custom bumper for a car. I am familiar with the mold process but what I do not know is what type of expandable foam I should buy. I am planning to make a wooden box ( form) to pour the foam in, then attatch it to the car and start cutting and sanding to get the desired shape. What I need is something that will expand and still be closed cell enough to handle cutting, sanding and shaping, then can handle bondo being applied to get that oh so smooth ready to be painted, finished buck.

Tap plastics used to sell a resin foam, it was pretty tough stuff, but a little on the heavy side. My project cam out like sh*t but thats just me.

Use polyurethane two-part foam, The foam from diy shops is rubbish for your purpose - it leaves big holes as it expands.

I don't have much experience, but if you want to pour foam, use a 2lb poly foam. To let it cure nicely and keep from being super porous, you probably will want to pour in multiple stages.

It might be easier to used closed cell insulation-type foam from Home Depot or Lowes (the blue is typically used), and form with a hot knife and then belt sander.

Have you considered using Styrofoam and shaping it instead of a using a mold.
I have done things this way as well as it is the standard for making fiberglass surf and sailboards.

Just throwing it out there....

Try looking at some of the projects on here.....

http://www.fiberglassforums.com/

I'm a member to this forum and they have some good folks that can help you out.

This place seems to have a lot of information. I did a bunch of reading there a few years ago, but haven't been able to put anything into practice yet.

http://www.fiberlay.com/

edit:

The expandable foam link is on the left, couldn't get a good link directly to where I was trying to show you.

Order some surf board blanks

There's surf shops all over on the Left Coast

I see the pink insulation boards that you can get at Home Depot being used a lot. I plan on using them when I make a new piece for my car.

One of the shows I saw on TV used sheets of florist foam...they laminated sheets of it together with gorilla glue to get the thickness needed and then shaved it down to shape. They were making fender flares.

Mike

The spray on foam seems to be used also...


Before

Click to view attachment

After

Click to view attachment

Scotty,

Use the simple spray foam and cover it entirely with plaster or paris.
the plaster will not degrade with the fiberglass epoxy.
Use the plaster like bondo.
Rich

comes in 914 colors

Use the pink stuff from Home Depot. You can rough the shape in with a course wood file, then finish sand to shape w/ 80 grit sandpaper. But, you need to cover it with something before laying fiberglass over it, the resin will melt the foam.

I just used it over the holiday to make a mold for my "GT" seat project. Worked great and now I have two 914 seat shells w/ extended bolsters. Next step is to learn how to do upholstery.

Click to view attachment

Click to view attachment

Click to view attachment

I have used the spray foam. Cheap and easy, oh ya

The sheets and particularly spray foam just isn;t going to cut it. I'm talking about a whole front bumper. That stuff may be great for a small project or a home doer, butI have to keep this within a reasonable budget. Surfboard blanks crossed my mind but the amount I would need would be $$$$ plus shipping got to be even more $$$$$$. I am looking for expandables because they are smaller to ship, they will fill a large box fairly quick and easily, and it looks so cool when it starts to grow I'll check out the sites Paul and Jim posted Mike, I hadn;t thought about florist foam, I know I can get that locally in large chunks but will it hold up to the ibeglass resin ? A lot of foams will disolve. I will be making a female mold off of the buck, but will keep the buck just in case. If this turns out well I am going to try and sell them. Under wraps for now so dont ax not for a 914 though, but it is in la familia

Shhhh

Yer phone is broke

Yes the green foam used by the flower folks will not get eaten by the resin. I just used some today.

This place has all the "glassing" supplies you'll ever need.
http://www.cstsales.com/
I used thier Rohacell foam when I had to modify my front bumper. The stuff is a little spendy but works very well.

Paul

--><div class='quotetop'>QUOTE(scotty b @ Jan 5 2011, 10:08 PM) </div><div class='quotemain'><!--quotec-->
The sheets and particularly spray foam just isn;t going to cut it. I'm talking about a whole front bumper. That stuff may be great for a small project or a home doer, butI have to keep this within a reasonable budget. Surfboard blanks crossed my mind but the amount I would need would be $$$$ plus shipping got to be even more $$$$$$. I am looking for expandables because they are smaller to ship, they will fill a large box fairly quick and easily, and it looks so cool when it starts to grow I'll check out the sites Paul and Jim posted Mike, I hadn;t thought about florist foam, I know I can get that locally in large chunks but will it hold up to the ibeglass resin ? A lot of foams will disolve. I will be making a female mold off of the buck, but will keep the buck just in case. If this turns out well I am going to try and sell them. Under wraps for now so dont ax not for a 914 though, but it is in la familia
[/quote]

Worse comes to worse.... cover it in aluminum foil. Then glass over it to make your mold. I've never personally used it... but that's how they did it on the TV episode.... I think it was the show Musclecar on SpikeTV.

Mike

Plastic wrap can work as well, no?

that's for wrapping around the middle to help you lose pounds.

anti wrinkle cream there might be.... but anti fat bastard cream there ain't

No, the final buck needs to be perfectly smooth and actually painted as if it were the finished bumper. That then gets coated with mold release, gel coat and then the glassing begins. THAT makes the female MOLD that the real parts are made from. That is why the initial buck needs to be bondo'd and worked to perfection, any imperfection will come out in the gel coat on the female mold.

SWEEEET a battle of the bigguns. Someone call Donald he needs in on this

--><div class='quotetop'>QUOTE(scotty b @ Jan 5 2011, 08:08 PM) </div><div class='quotemain'><!--quotec-->
The sheets and particularly spray foam just isn;t going to cut it. I'm talking about a whole front bumper. That stuff may be great for a small project or a home doer, butI have to keep this within a reasonable budget. Surfboard blanks crossed my mind but the amount I would need would be $$$$ plus shipping got to be even more $$$$$$. [/quote]

You're not going to find anything cheaper than foam sheet and the spray can foams. Here is a shot of a ricer that had his front bumper using the only stuff from Home Depot, so it can be done on the cheap. Fill in the voids with the spray foam and make your female mold. It will take some work to get the mold perfect.

Click to view attachment

[quote name='URY914' date='Jan 6 2011, 05:01 AM' post='1414236']
--><div class='quotetop'>QUOTE(scotty b @ Jan 5 2011, 08:08 PM) </div><div class='quotemain'><!--quotec-->
The sheets and particularly spray foam just isn;t going to cut it. I'm talking about a whole front bumper. That stuff may be great for a small project or a home doer, butI have to keep this within a reasonable budget. Surfboard blanks crossed my mind but the amount I would need would be $$$$ plus shipping got to be even more $$$$$$. [/quote]

You're not going to find anything cheaper than foam sheet and the spray can foams. Here is a shot of a ricer that had his front bumper using the only stuff from Home Depot, so it can be done on the cheap. Fill in the voids with the spray foam and make your female mold. It will take some work to get the mold perfect.

Click to view attachment
[/quote]

I like that fancy holding device. As for the foam I would have to agree with using the pink stuff and just layering it to get the size you need. I've noticed that the florist foam stuff costs a little more per volume than the pink stuff..

The polyester resin will eat up a lot of stuff and most foams. Surfboard blanks are made of polyurethane foam than can stand up to the polyester resin. I made a mold of my targa top and the polyester resin ate thru all the wax mold release compound and wrinkled up the paint. Try using an epoxy resin for the first layer of your mold. The epoxy will not melt thru the various materials. After it cures, you can add a bunch of stiffening layers to the mold using the cheaper polyester resin. FWIW

Florist foam, the green stuff, holds up to "some" resins, but not all.
Some of the epoxy resins will eat up that type of foam also.

Still, the cheapest way to go is pink foam for major build, spray foam for the cracks...smooth it all out and use plaster to cover the whole thing and smooth it out perfect.

try this place.
www.foamation.com

rich

O.K. I'm going to try the pink foam since it is both cheap and local. I'll post pics when I get to that point. I won't be starting this for a couple weeks. Thanks much for the info

Woo hoo!! Pics ROCK!!!

at last we'll see what this secret non-914 project is.

Then I can copy you and make a ricer front end for my car that is still 914-esque in style.

Drywall mud? Or is the same thing as plaster?

Stay away from from the polyester resins; unless you like shrinkage and warpage. And I can only imagine how that long span will twist on you. Try this: http://www.aircraftspruce.com/menus/cs/epoxy_aeropoxy.html
http://www.aircraftspruce.com/catalog/cmpages/rutan.php
or my favorite
http://www.aircraftspruce.com/search/searc...ss&search=1

Is weight a factor? If so, you'll need to fab up a vacumn bag set up, also.

Scotty b,

Definately worth your while to go to the fiberglass forums as URY914 suggests. Follow his link; I believe there's a auto body exterior section (or something like that). Everything in this thread and more is discussed there, plus you're likely to get many other valuable tips, tricks, and ideas. You'd be remiss not to go there.

Andys

The cafe racer board I frequent also swears by florist foam and when necessary cover in foil for that first layer to preserve the mold. Back in my model airplane days, I would use monokote(sp) to save the mold and function as a mold release too once waxed. Think of that as iron on adhesive backed mylar shrink film.but that's my experience.

I believe Blueovalz did his car using the florist foam - might try contacting him for any tips? He obviously knows his way around doing foam and fiberglass body mods:
http://www.cardomain.com/ride/2168777/1971-datsun-240z

He currently posts on the Yahoo/Manta groups site - switched his focus to doing a full tilt LSx powered Mirage.

Jeff