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Proper Use of Expanding Foam in Automotive Applications

Proper Use of Expanding Foam in Automotive Applications

Despite the obvious drawbacks - it's messy, sticky and impossible to remove once it cures - there is nothing better than spray foam for sealing air and water leaks (and so much more!).

expandi foam - bodywork made easy - ready for bondo and paint

Cut Cured Foam With a Bread Knife
A serrated knife with a flexible blade is perfect for cutting off excess foam. Just make sure the foam is completely cured and firm all the way through or it'll stick to the blade.

expandi foam - bodywork made easy - ready for bondo and paint

Seal Foam With Foam
It's well worth the effort to add insulation and seal any cracks and gaps. A good DIY approach is to cut rigid foam insulation to fit between the gaps.
Cut it about 1/2 in. undersized so it's easy to fit in. Shim the rigid foam in place with little chunks of foam. Then fill the space around it with expanding foam.
Don't forget to caulk or foam the joint between the sill plate and the foundation too.

expandi foam - bodywork made easy - ready for bondo and paint

Leave Accidents Alone
When foam goes where you don't want it, you'll be tempted to wipe it up. DON'T! You'll only spread the goo and make the mess worse. Instead, let it harden completely and then scrape or sand it off.

expandi foam - bodywork made easy - ready for bondo and paint

Big Holes Need a Double Dose
Some holes are so big that the foam starts to sag. For large holes like this, the trick is to fill the perimeter, let the foam cure and carve it off. Then add another layer to finish the job.

Remember, It’s easy to underestimate how much your foam will expand. This leads to overflow splurging out of nooks and crevices! If you drop the foam on the floor or spray it in an area that you don’t want it, wait until it’s dry. You’ll be tempted to wipe it up straight away, but don’t! This’ll just spread it and make the mess worse. Once it’s dry, carve it off the surface with a knife, sand the area, and re-paint if necessary.

With some practice you will achieve a professional finish in no time!

8.11.07

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