Fiberglass Work

[MR2-M1]

I have an MK1 with a fiberglass BMW M1 bodykit. I am in the process of repairing some fiberglass on the front. In the past I used woven cloth, but the areas I repaired have broken away. Granted this was several years ago but nonetheless they are in need of repair. So my question to you is, what is better for fiberglass repair, woven glass or stranded glass? Any info would help, thanks.

J

[canadam]

It might depend on the particular damage you have. Some experts around here should be able to help you

[turboguy]

Originally Posted by canadam

Some experts around here should be able to help you

I guess this is where I step in.


A chopped strand mat works great for a repair like that. Since I'm assuming you are going to paint this, the weave pattern won't bleed through like woven can.

Cut out the entire damaged area. DO NOT fiberglass over the damaged or delaminated glass. It won't hold. The easiest way to do this it cut out the bad part with a dremel and cutoff wheel. After you have your area cut out, remove the paint in the surrounding area and scuff it up good. Fiberglass won't stick to paint that well. Make sure the area is cleaned with an automotive prep wash and a tackcloth to remove anything that the resin might not stick to. After that, put duct tape accross the back to kind of form a reverse mold of the area you will be repairing.

Get out your mat and resin and measure up. Mix the resin per instructions. There are many different kinds such as a polyester which uses just a few drops of hardener to a cup of resin to epoxy which has more of a 50/50 mix. The ideal ratio of resin to fiberglass is 1:1. Weigh out the amount of mat to be used and weigh out the same amount of resin. This will make the strongest repair without oversaturating or using too little resin.

Now, saturate your glass mat with resin and press it into the area you are repairing one layer at a time. Let each layer set up for approx 15 minutes, or until the resin is tacky. Use a squeegee between each layer yo remove any trapped airbubbles and excess resin.

After you have the repair built up just above the surrounding surface, remove the duct tape from the back of the repair and add a couple more layers back there. This will further stiffen the repair.

Now, I'm sure you know how to use a sander, so, just sand the front smooth with the surrounding bumper. After its sanded smooth, you will notice little pinholes in the surface. This is almost unavoidable in doing a repair of this type without expensive equipment.

Once again, use the prepwash and tackcloth to remove any dust/grime. Now, break out the glazing compound (Bondo makes some very good stuff) and squeegee a layer ofer the repair making sure to work it into the little holes. Let this cure COMPLETELY before sanding. It usually takes about four hours. Sand smooth and repeat until the little holes are gone.

Clean it with the prepwash again, prime, and paint. Now you are done!!

[MR2-M1]

Thanks for the advice Turboguy. As mentioned before I have have done this before, but obviously didnt do that good of a job. I didnt clean it as good as you suggested. I also used woven cloth, and I didnt even know about weighing the mat. One more question, is this the same method to get rid of stress cracks? There are a few around the whell wells.

[turboguy]

Stress cracks are easier to fix. Take a dremel with a "V" bit and chamfer the edges of the crack inside and out. You're going to make some fiberglass paste here. Take a piece of woven fiberglass cloth and cut it up into really small pieces. Pull the fibers apart and try to make it as close to the consistency of sand as possible. Mix it 1:1 with resin. It is important you have a very accurate scale for this (talking grams here)

Apply the paste into the chamfered crack (you remembered to clean it, right?) Let it cure and put a couple layers of mat on the back side bridging the crack by at least 3 inches in either direction. This will help in keeping that crack from returning further down the road. After it is all cured and reinforced, sand down the outside, fill any pinholes, paint and go.

[feral4mr2]

a bit off topic, but would you mind posting some pics of your bodykit? or pm me with some.

thanks.

[PHOENIX]

^agreed, lets see some pics!

Originally Posted by Turboguy

A chopped strand mat works great for a repair like that. Since I'm assuming you are going to paint this, the weave pattern won't bleed through like woven can.

Could you explain why this happens a little more in depth? The reason im asking is I used both on my MR2 and havn't had any problems since the work has been completed. How does it bleed through since everyone that fiberglasses knows that a layer of bondo is used to catch the pinholes and imperfections before primer and paint?

I don't mean to second guess your statement, im just curious.

[MR2-M1]

I have lots of stress cracks, grinding with a dremel seems to take forever. I have decided to go with 100 grit on a smal angle grinder. Im just grinding enough to take out the stress cracks. There are several cracks throughout the front piece. Some are contoured edges. I planning on laying woven cloth as suggested above to help reinforce the remaining glass. If I could find on I would just by a new front clip.

MR2-M1

[turboguy]

Originally Posted by PHOENIX

Could you explain why this happens a little more in depth? The reason im asking is I used both on my MR2 and havn't had any problems since the work has been completed. How does it bleed through since everyone that fiberglasses knows that a layer of bondo is used to catch the pinholes and imperfections before primer and paint?

I don't mean to second guess your statement, im just curious.

Paint is not 100% opaque and can react differently to some materials. That is why a urethane bumper, a steel fender, and a fiberglass hood (for example) can be prepped the same and painted the same color, but have a slightly different color to them. This isn't as common in high quality paints anymore, but still can happen.

When a glaze coat (compound or bondo) is applied, its not used to build any thickness, just to fill pinholes and slight imperfections. After it cures, its almost completely sanded off to smooth the surrounding areas. With a woven cloth, there are high spots and low spots. The low spots fill with resin or bondo. The high spots are cured fiberglass. When you sand, you can have kind od a checkerboard effect of fiberglass and resin. After painting, this pattern can "bleed through" even if the surface is completely smooth. This is most common in blues and deeper shades of red.

When fg mat is sanded, it has no discenrable pattern to it. Its just a chopped strand mat. There are high and low spots too, but there are also various "in the middle" spots that help even everything out. The randomness of chopped strand helps to avoid any patterns that could possibly show through on a finished part. This is one main reason that almost all commercially produced parts use chopped strand mat.

I hope that helps a little bit. My brain is kind of fried today. I get to do this all day at work too.

[PHOENIX]

you explained it perfectly, thanks!

Im an amateur fiberglasser and body guy, i worked in a very successful body shop for awhile and learned a lot, even did my own car under the guidance of the shop owner.

But I don't have the experience to know all the little things like that.

[toyotaspeed90]

well it also depends on the prepwork..... i learned first hand when making the glass hood for my ae92 (which is still unfinished... i'm not a huge fan of working with composites... but i do know how to)... i initially got some help from an ex-roommate whom had worked at a successful bodyshop as well... but the shop taught him many wrong ways (and he WAY WAY WAY over-resined everything)...

the best way to get good results obviously is to vacuum bag the parts.... strangely enough this can be done relatively simply, but not many do it (and I don't.. since all I make are parts for myself)

in any case.... i personally tend to over-accumulate layers on purpose... then go back over everything with the die-grinder..... gets it to a somewhat flat surface.... i've actually had better luck with woven & bondo coming out in paint than mat & bondo....