Would you fibreglass them?
 

I'm trying to make rear wheel skirts for my car but there is a problem that the body of my car curves in very agressively from way above center line of the wheels,therfore the wheels are sticking out so I could only put a little hitler moustache on for wheel skirt as it is, which would look silly and possibly not do any good for aero.

So I decided to bring the body line out at least close to flush with the wheels by creating these...I don't know what to call them wheel air deflectors/fairings?

I want a descrete look so they are going to be painted to the color of my car and clear coated.
Since they are made out of styrofoam,before I can apply any Bondo or primer I will have to either tape over the entire foam surface or (testing now) use spray adhesive and wrap it in aluminium foil so the foam does not melt away due to the chemicals.

My question is: Should I fibre glass over the fairings (over the tape or alu foil)?

And then Bondo,sand,primer etc. Or just skip the fibre glass and Bondo over the tape or foil and continue paint prepping.

What will I gain fibre glassing them? Besides that it will take a kick or a rock better than without it.

Easier mounting due to better structural strenght?

Please share your experience/opinion and give me a reason to go either way!
I just don't want to mess with the glass unless there is a good reason.

In the pictures you will see the piece trailing the tire is already wrapped in alu foil so it is hard to see. The piece in front of the tire is bare foam. And in the car pics the silver part is held up to the car by a piece of scrap foam against the ground,don't let that bother you : )

Thanks!
Barna

dude, those look really cool. Did you shape those by sanding down a bigger foam block?

IMO you will want to fiberglass them first. Bondo is really more of a surface prep, and not designed to be structural. It's very brittle and I suspect if you just layer bondo over the aluminum foil you will find it cracking like an eggshell and then flaking off. If you do a layer or two of glass this will give it some structural rigidity and the bondo can be used to smooth it for paint prep.

Thanks Geo! Makes perfect sense the way you put it. I will actually wrap them in tape then foil to try to protect the foam from not only the fibre glass seeping in but the heat it might make during curing. They are relatively large pieces and as much pain in the butt they were making,I really don't want to repeat.
As to your question,
I wish I had a large enough block of styrofoam to start with but no these are 2" thick insulation sheets hot glued together and then I used everything from razor knife, saw blade , hot wire (mostly for the inner curve a half loop of heating wire from a hairdryer on 12V DC) sanding block etc. to shape them. Challenge to match the compound curvatures of the rear bumper.Lots of fitting and shaping!

Thanks for the input!

Barna

I'd recommend fiberglass cloth (6 oz) in epoxy. If you lay it on the bias it will form a compound curve easily (in other words, it stretches very easily on the diagonal). Epoxy works very well with styrofoam, unlike polyester resin. Also If you are doing this at home, it doesn't stink up the whole house the way polyester resin does.

The nose on the Zing! was made like this. After the fiberglass is on, then you can use bondo to fill in any little dings from sanding the foam.

The disadvantage to epoxy is a longer cure time, and higher cost.

old school traditionalists use latex paint - house paint - to paint the styrofoam so the fiberglass doesn't eat away the styrofoam. use several thick coats.

then pva on top, then make your mold.

@Ken Fry- Thank you for the advice! My biggest issue with epoxy resin is....that it is not on the shelf for me to purchase! ( in lowes or home depot ) So I have to go find a boat place somewhere and/or ask around/run around to find some.
I have 4-5 packages of cloth but it does not state how many oz just says 8 square ft. I guess the typical stuff that comes with the polyester resin as a repair kit. I will have to talk myself into aquiring epoxy resin! It would make working with styrofoam so dang much easier.
BTW the Zing is very cool!

@drmiller100- Thank you! I would never had thought of using latex paint to coat the foam! Awesome! I don't think I will make a mold as I don't plan on mass peoducing them unless I saw a bunch of old proteges running around : )
Thanks for the ideas!
Barna

I have used white glue to make a barrier before with good success. You might want to try the resin over some scrap pieces that have been coated with glue or paint first, just to be sure you like the result. Awesome job on sculpting the foam. Making the other side to be a perfect match might be harder than the first set though. I'm no expert, but from what I've read here, air flows off of sharp edges better than rounded ones. You may want to square off the ends of your rear mold or give it a sharp edged reveal at the back like the new Prius. I'm looking forward to seeing the finished result and hearing how they function. I'd like to do something similar on my car someday.

Thanks!

I use RAKA epoxy (ordered via internet), which is not too awful in price. There are all sorts of fillers you can add for various purposes, including making stuff like body putty -- although I have usually found Bondo quicker and easier (other than the fumes) to work with.

The Varieze (a Rutan experimental aircraft) was made with glass in epoxy over styrofoam, in a process called moldless composite construction. Aircraft Spruce and Specialty used to sell a book written by Rutan and a kit of stuff to experiment with. Dunno if they still do.

At the time when the photos were taken,I already had the other side done. Before I started on it,I was thinking that it will take a fraction of the time making it as it did to make the first one due to the fact that I can just kinda copy the mirror image of the piece in front of me,faster rough cuts etc. However I ended up fiddling with it about as long as the first piece took to make!
Funny that you mention the sharp rear edge! You can't tell from the pics but it does protrude a little past the rear curvature of the bumper (about less than an inch) and the inside has a sharp flat surface filling the gap back to the rear of the bumper. Little batman wings. I doubt it has any significance because it is really behind the bumper at that point but that's how I made them anyhow.

It will take some time for me to complete them due to my job interfering with my tinkering (fortunately I might add) but I will post progress here! Thanks!
Barna

3dplane, where in Florida are you? There's a fiberglass shop in Daytona Beach called US Composites that has epoxy resin, and for good prices. If you're not nearby, you can mail-order it. Their website is uscomposites.com