Leave foam in new panels or not?

[Don]

A discussion about whether to keep foam in between adjusted panels came up in a buod thread so I thoughtI wouidl start a new discussionn here to get more folks input without fillingup the buiold thread.

Wayne (dobie44) added new, wider fenders to his 308 panels to get a 288 GTO inspired body. The foam used was the stuff you can buy from Home depot that in sheets.

We took the rear clip off after he fiberglassed over the top with 4 layers of 1.5 oz mat and resin. At this point, he is about to either cut the old skin out and remove as much of the foam as he can or leave it as it is and concentrate on cleaning everything up on the outside.

Question for everyone:

Should the inner skin and foam be removed and a couple more layers of glass be laid on the inside or can the foam stay in place?

Looking for experience, opinions and examples if possible please.

Thanks
Don

[Don]

I will start the discussion.

I have always been an advocate of removing all the inner panels and foam to reduce weight and add more room inside. I also usually used the expanding two part foam in my parts creation/adjustments.

I remove the foam so that there will not be any expansion and continued off gassing of the foam under the new skin that may cause expansion and cracking etc. Seemed like a prudent thing to do but I have never seen any hard evidence or examples that contradicted or supported my thoughts.

Given that the foam used is the Home Depot variety which will have long ago off gassed, is there a danger of expansion in the heat of the sealed foam/air pocket between the two skin layers? Not sure.

I am coming around to the thought that the foam doesn't really need to be removed and that will save a ton of work and time on the project...

I open the floor to others....

Cheers
Don

[murcie-me]

Um, why is there foam behind your panels in the first place?

[Don]

Murci-me;

There is foam because Wayne added foam to the rear quarters and back panels and carved it to shape before putting fibreglass over it. He wanted to create a 288 GTO inspired car so started with a set of 308 panels and added foam to get the wider stance etc.

Cheers
Don

[TDW]

I'm of the opinion that the foam used for shaping a panel should be removed after the outer skin has been "finalized".

The so-called "proper" way (at least what I was taught) to make a new panel is to create the plug, finish it to perfection, make a mold, take a part out of the mold to use as your "final" part. This is not always practical, so doing one-off's is not uncommon, BUT removing all the "stuff" that it took to create the new one-off part, makes it most like an ideally created, finished part out of a mold.

The foam and original glass is not going to "hurt" anything by being there, it's just not very pretty and does add weight and bulk. Taking it all out is allot of work, but after it's done, you can lay in a layer of fresh matte (or cloth) and it will resemble what you'd have ended up with by doing the long way around with the plug-mold-part method.

I guess another approach would be to lay an additional layer of thin (like 3/4oz.) matte on the inside, sandwiching the foam and original panel in between itself and the new outer panel. Good insulation?

In the end, it's up to the individual what they want to end up with.

[dobie44]

Thanks for starting the thread Don this will be interesting reading!

[RCR]

I don't think there's anything "wrong" with leaving it. It's not much different from using a laminated core from my perspective. Just a matter of personal taste...

Bob

[RHK]

Is there any way that the foam could absorb water? If so, I'd be concerned that it could mold/mildew or freeze and warp. I'd be really tempted to leave it, but I think it'd be best to remove it. Just my opinion though.

[dratts1]

foam core adhered solidly to an inner and outer fiberglass skin would be far more rigid than just the outer skin. The outgassing is something I have no experience or opinions on. Water absorption would depend on whether it is close celled foam or open cell and even then I have no idea whether it could be an issue.

[TDW]

I was told by the man I learned fiberglass from, about a project he did early in his own career. It involved a race car body that the owners wanted to make as light, yet as strong as possible. They had done quite a bit of work to all the rest of the body to lighten it, but they were drawing a blank when it came to the doors. My understanding was that it had to be at least as strong as it was from the factory, which meant they couldn't just leave the outer skin and pitch everything else.

To make a long story short(er), he made a fiberglass reproduction of the inner and outer skin, and put foam (not sure what kind, but he worked allot with triple expanding when I knew him) in between. When the owners asked him if it was strong enough, he suspended the finished door between two chairs and had them stand on the middle. The "sandwich" construction makes a structure very strong.

In the case of Wayne's car, you already have the inner "skin"(the original panel), the foam was added and is already sandwiched between glass. Only thing you might want to do is make sure it's sealed good at the bottom.

[MacGyver]

So far it seams like everyone thinks leaving foam in shouldn't hurt anything. I think I am going to disagree with that one. The panel may be stronger but I believe it will be prone to warping over time. Once the panel is out in the hot sun and winter cold, the foam may swell or shrink causing waves on the body panels. I think it would be much safer to remove the foam.

[Havemurci]

I used the foam from the local home supply store once and over time the stuff continued to expand and warp the panel,had to cut into finished bodywork to relieve the pressure.
Just my .2