Hey there, I have a fiberglass heater box that is in good shape, but the fiberglass is kind of dry. Its not cracked or broken, and doesnt need any real repairs. I have heard of people "soaking" fiberglass with resin to get the resin to soak back in so it isnt as brittle. (usually associated with Corvette body repair) What is this process called, and what can I use to do this? Im not finding anything really online and my search here only brought up stuff for fixing cracks and adding shapes to already cured stuff. Im not sure what this is, the only thing I can think of is "reconstituting" fiberglass but that doesnt sound right. Thanks!
You can thin polyester resin up to 10% with acetone. Make some thin resin, amount of hardener based on amount of resin before thinning. Heat the part with a heat gun. Not melted but hot to the touch. The warm part and cooler resin will draw in the resin to replace contracting air. If the part is cold, the heat of catalyzing resin will expand trapped air and make for bubbles (works for epoxy on wood too). The heat will kick off the resin faster, you aren't building anything, shouldn't be an issue. The surface should level out and look nice. If you really want a better surface, vacuum bag, it's not hard and YouTube is your friend. You could use epoxy the same way, it sticks good to old, porous, polyester/fiberglass (maybe not so good to gel coat). Epoxy thins with denatured alcohol, lacquer thinners and acetone. It stinks less. Heck, I wouldn't be afraid of a couple coats of epoxy rattle can paint. Mike
Thank you for that! Would you have a preference of using the resin, or using the epoxy paint? Ultimately I would like to respray the firewall black, and the heater box to match, but too, this isnt going to be a show car and Im not planning on keeping it. I would like to do the job right so it lasts and works.
Are you sure it is fiberglass? I am picturing a heater box in my mind and I couldn't say positively that it was made of fiberglass. Just saying that if you aren't sure, you might be better to verify first.
What you got there is SMC or sheet molded compound , or really shity fiberglass , it has to be repaired with SMC resin, not fiberglass resin !!!
Yeah, that's the stuff I was picturing in my mind. Although I agree that it is somewhat similar to fiberglass, I just don't think that's what it is made of. Luckily it looks like Larry K has an answer for you
Is the method of "soaking" this the same as mentioned by Accurate Mike? Or will there be specific directions on the container?
Got curious, did a search on the "interweb", from what I can see there are two processes, SMC and BMC, I think what you have is BMC which is resin and fiberglass strands injected into a mold. To fix what you have the first thing you'd have to do is strip the paint off by grinding or sanding as you can't use paint stripper (the chemicals would stay in the pores of the part), then you'd have to identify what resins were used as they are not interchangeable or compatible, then apply resin, cure than sand. Instead of fixing what you have it may be easier, quicker and cheaper to find a replacement.
BMC usually uses very short fibers. I do not think what is being shown is BMC. SMC is smooth on both surfaces unlike fiberglass that will be rough on the bottom. SMC also does not have any sort or gel coat on it.
You said there is nothing wrong with the part , correct ? your flipping the car if I read this properly ? Clean it , paint it , call it done . It’s a heater box , not a stressed suspension part that requires attention. if you have some soft spots or questionable areas use some 5 minute epoxy and be done .
Hello, It is a type of sprayed-in fiberglass compound from a commercial application. Near our old Westside of Long Beach house, were several different boat manufacturers and their outside yard was always in use with boat hulls, cabinet forms, plus other barebones parts. They had this hose connected to a giant pump and there was a mixture coming out of the hose that looked like thickish, white glue with stuff in it. The guys were fully covered including eyes and mouth. They proceeded to spray the inside of the hulls and the other molds. This created a surface that was eventually strong and with many other layers, provided structure to the empty hulls. Some manufacturers made different molds for other fiberglass sprayed items. We lived about a mile away and downwind from the ocean breeze that was a guaranteed happening everyday. The West winds came wrapping over the coastal hills, into the lower flatlands and blasted anything in its way, every afternoon. We grew up smelling fiberglass aroma from elementary school through high school and beyond. Jnaki In our later sailing years, we had several sailboats that had various methods of building from different manufacturers. Some had single layer sprayed on fiberglass hulls. If one could see the interior walls inside of the non public areas of the sailboats, the surface looked like that photo of yours, but in a nicer condition. If the area was in a public portion of the sailboat, then it had an additional smooth coat applied and looked like a nicely finished surface. It depended on where it was on any boat. Hidden, rough, exposed to sight daily, smooth additional layer sprayed on top was usually the case. If you ever follow boat building, there are some manufacturers that add in a second layer creating a dual layer outer hull for insulation and structural protection. Those are on the higher end boats and if you are inside during a cold winter night, then there will be no moisture building up on the inner surfaces. With a dual layer hull and good finishing components, the insulation makes the inner surface warm and show no moisture. The single layer after a night's sleep, one can see moisture on the inner surface and water dripping down to the bilge. It was/is a normal happening. So, it is sprayed on fiberglass and you cannot put on anything to melt the components. Various commercial enterprises were contracted out to built different specific parts for different factories. The process was/is dangerous and hazardous. If you sand or grind, make sure you wear an air purifier mask not just a white paint face cover. But, you can add on a smooth compound of something over that funky surface material, if it is prepped well. YRMV
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