Thread: fibergalss fun

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Like the title says, having some fun working fiberglass.

One thing I figured out on my own, a heat gun is your friend! Especially on a cool day.

So, some questions. How economical is the bondo brand fiberglass kit?
Is there a cheaper and available alternative?

When do you use matt, and when cloth?

I have always used brand name fiberglass kits. There are a few but I never used the cheapest . I always found cheapest is just that, crap.
I like using cloth in areas that require some strength. I also will sandwich either pieces of aluminum or steel between the cloth for strength. Matt is good for hard to get areas because you can soak it in the resin and remove the air bubbles then push it into the area.
That's the biggest reason why some matt or cloth will fail...........air bubbles........make sure you force them all out so the cloth and/or matt is see thru. I have always used a stiff bristled brush with the bristles cut back to dab on the cloth or matt to force out bubbles. I have seen guys use a roller and that works but you better get it clean or you use it only once.

west systems .

Mat goes on the outside (near the paint surface), and can be "rough" sanded, cloth (the stronger of the two) goes underneath the mat, you cannot sand it and paint on top, it would have to be covered with bondo as when sanded the strands become visible. If its on the outside of a vehicle I would only use tooling resin and punt on the cheaper parts store resin, order offline from a supplier. Tooling resin is harder, stronger and doesn't shrink near as much as standard resin, and when ordered offline cost is marginal. Cheaper parts use cheaper resin, its easier to work with and sands easier saving them time. I did a post earlier on fabbing glass parts by starting with foam but don't know how to get back to it...

veil cloth works good if your repairing . lay it over the cloth . i use epoxy resins .

Originally Posted by Matthyj

...I did a post earlier on fabbing glass parts by starting with foam but don't know how to get back to it...

Left click your screen name, and then select "View Profile". There you can select "Find all started threads" if it's one that you initiated, or "Find all posts" if it's something you added to someone else's thread. That's the quickest/easiest way to find your old stuff that I've found.

Most fiberglass bodies are made of multiple layers of mat, with just enough resin to saturate the mat. You can buy mat in different weights (thickness). The Bondo product takes 3-4 layers to add up to 1/8". I would never sandwich steel or aluminum with fiberglass, to make a part stronger. The rates of expansion are much different between the materials, with the steel being far lower than the fiberglass or aluminum.

Fiberglass body builders found out long ago that glassing steel reinforcement to the inside of a body would result in read-through, where the reinforcement would show through to the outside.

It's always more expensive to buy resin in quarts, but if all you need in 1-2 quarts, a gallon would just go to waste. It doesn't keep forever.

After I worked it down and sanded it smooth, I applied a skim coat of resin to fill some tiny holes, and it isn't curing fully. Undoubtedly I was a few drops shy on the hardener. It's still slightly tacky, just enough that I can't sand it, even though it sat in the sun all day.

Any tips to get it to fully cure? I seem to remember that in the past I have mixed some more resin, super "hot" with hardener, and skimmed the part.

Try using a heat gun, if the area isn't too large. Don't over do the heat. An oven cure could be used on a small part. It's important to get enough hardener into the mix. For small batches, you need to have a reliable measuring device and use 10-12 drops per ounce (for the Bondo resin). I've done most of my fiberglass work in the winter, when my shop is only at 68 degrees and never had a curing problem. If I think that the resin is curing too slow, waving my heat gun over the area (briefly) has always done the trick for me. I have a 1 ounce measuring cup that I use for small batches.

I found one small area on one of my fiberglass fenders where the resin was still gummy, after more than a year. The car had been out in the sun a lot, but that didn't do the trick. I ground the gummy material out with a rotozip bit and applied new fiberglass to the area.

Firebird, the amount of hardener is extremely temperature sensitive, and is also specific to the product you're using. For example, the can I have right now says for ambient 91F and higher 10 drops/oz, 71-90F 12 drops/oz, and 60-70 18 drops/oz. If you mixed it light and it didn't harden you've used up the reaction of the MEKP and no amount of heat is going to cause the required catalytic reaction at this point. Mix up a small batch, enough to put a light coat over the problem area, and go up to 50% higher on the MEKP than called for. The new layer will react with the surface of the old, sticky stuff and you should be OK, provided you didn't put it on too heavy.

I use a shot glass marked in fractional ounces for the raw resin, to be accurate on the hardener to resin needed, and pay strict attention to the temps.

i buy paper mixing cups from taps warehouse . in cool weather preheat the area before applying the resin .

Originally Posted by shine

west systems .

Shine nailed it!! Get the video or maybe youtube!! Great tips on thicken the resin for vertical and overhead work!!
WEST System 105 Epoxy Resin Pete

Firebird, I would try to refrain from making a part simply out of mat, as mat needs backed with cloth for strength. If mat only is used and the part is stressed its going to be prone to cracking. I always back my mat with cloth on the backside and not the little thin cloth you find at the auto parts store, I head to a boat repair or a fiberglass supplier and get both heavyweight mat & cloth. The way a body is made is in reverse, a gel coat is sprayed into a mold, then a few layers of mat is applied, its saturated with resin and the air bubbles are worked out, tear you mat don't cut it as a sharp line doesn't saturate very well. After the mat is put on the gel coat the cloth is cut and layered over the mat for strength, and it is saturated with resin, the strength is in layers. Unfortuantely when repairing or making small pieces we don't have a mold and we don't use gel coat so we go a little backwards we skim coat the mat with bondo and smooth it out for paint. I have cloth I purchased that has mat on one side already saving a step. I think we have all had the non cure part before, Rogers method might be worth a try as I generally scrape it out, old resin sometimes seems to do this. I have never used the epoxy resins but the nice thing I don't think they dissolve foam but I see it can't be used on some mat?? check out the fiberglasssupply web site for supplies, great prices. I found some really great videos on youtube for fiberglass work, nice tips also. My best tip is use safety glasses with the mekp, I read somewhere if it gets in your eye you have only a few minutes before permanant blindness (found that out after using it several years!)

I did another skim coat, super 'hot' and let it sit in the sun. That did the trick.

Unfortunately, I worked it down far enough that I found another air bubble. So, laid in a tiny bit of matt, and tomorrow I'll try to finish it out.

Tomorrow I'm finish sanding, It's looking good.