Fiberglass lay up

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Kez

Well-Known Member
Joined
Feb 27, 2003
Messages
1,230
I have seen three techniques laying up a mold

1. Brush resin on the mold then lay fiberglass mat or cloth on the mold.
2. Pre-saturate the mat or cloth with resin then lay it on the mold
3. Lay the cloth on the mold and brush resin on the cloth

I usually do #1 but almost always end up with a lot of trapped air pockets which would require a lot of work to get them out. I am wondering if there is other technique that work better.

Thanks,
kez
 
I use 1 as well. First layer is 1oz or less. Helps get into those tight spaces. Then I use 6oz on top of that. I bag which helps with the bubbles as long as there is enough resin in the mold to start with. Using a heat gun helps to move the resin around and get everything wet.
Mike
 
I generally put a thin layer of resin (epoxy) in the mold. Stand the mold on end to allow excess to run out smooth drips out and let the it tack off. Then lay a fine 3 oz layer of cloth in. I also try not to lay everything in one piece to keep from pulling the cloth from the surface coat. Wet the overlapping seams in the glass to reduce air entrapment. Then continue with lay-up schedule.

Hope this helps.
 
You did not say if you are using epoxy or polyester resin. Big difference. I am old school and if using polyester I would use #1 but you need an impregnating roller to get the air out. Thickness of mold depends on how much use it get's (how many parts your going to build), how strong you want it. I would use lightweight mat first then heavier mat with a layer of cloth every 2 or 3 layers if needed to keep the mat smooth. The first layer needs to be perfect-absolutely no air and let dry.(Try to have no air in all layers). Scuff lightly with rough sandpaper between coats and knock down rough areas. Make mold as thick as you think you need. I would suggest making the mold strong and well braced for good quality parts.
 
I got away from mat years ago, PITA to lay!

Now I brush a layer of tooling gel coat, add a layer of 6 oz cloth then two layers of 18 oz cloth. As Tommy said knock the bumps off between layers. If you use unwaxed isophalic (tooling) resin you don't need to sand between coats.

Done!
 
I basically use method #1 with epoxy resin. However, I mix up a thick batch of milled fiberglass and epoxy and lay it into areas where there are sharp corners that fiberglass has trouble getting into. As with Mike, I use a lighter layer of glass cloth first then heavier glass cloth. To work out bubbles, I rub the glass cloth and resin wearing latex gloves to massage the epoxy into the cloth. I still have bubbles which are filled later by brushing on a thinned layer of epoxy after sanding.
I use a spot lamp to heat the epoxy and it cuts the hardening time at least in half and in my opinion, appears to make it less flexible. A low temperature oven (100 degrees) might work better or for people in warm areas, put the mold out in the sun and bake it.
 
Thank you all for sharing your knowledge and experience. What prompted me to ask was my inability to get rid of trapped air pockets despite using a mat roller. I thought maybe if I lay the cloth dry on the mold and then brush the resin on it will be a better technique?

I am laying up a tunnel cowling and it will not be possible to get the mat roller into may places. I will probably need to use an acid brush to 'stab' the stubborn air pockets. In this case, I will be using polyester resin.

I stopped using gel coat years ago after spending over $100 for can of gel coat only to have it harden on me after one season. I have since use laminating resin with Cabosil and coloring agent mixed in.

One more question: I use PVA over wax as I am sure most of you do. Does the thickness of the PVA matter? Will a thick coat release more easily?

Thanks,
kez
 
Kez,

Below is the Epoxy Tool Surface Coat I use for my molds. It's available in quart packages. Works great and is repairable.

Bert Dygert

upload_2019-5-20_21-47-34.pngesin Ser
 
Sop up the excess resin or epoxy with paper toweling and especially in areas it pools if you are not vacuum bagging. The resin or epoxy has little strength in itself but is like throwing rocks in the boat as far as useless weight goes
 
Just assumed you were using epoxy. Never done poly. I did have friends when I was young that use it to fix their surfboard. As I recall its a little more on the thicker side then the epoxy I use now. That makes it harder to get in there. I believe the heat aint going to help as it will just kick the poly sooner. I would try lighter coats and build it up from there. Good luck
 
I finally got around to lay up the cowl. I have found that fiberglass mat conforms to compound curves more easily especially I lay up in small pieces. I used a layer of mat followed by a 6 oz cloth and the cowl is stiff enough.
I ended up using Cabosil and pigment with laminating resin instead of gel coat. It worked but there are voids. The biggest problem with polyester resin is the short working time.
The cowl is not pretty butIMG_0198 (1).jpg IMG_0197.jpg usable but I will layup another one.
 
Looks good enough for a race boat. Plus you did it yourself!

A trick I found to getting more working time out of polyester is to mix only the right amount of hardener, IIRC it's 1%. A graduated syringe works well for this. Also after mixing pout it into several smaller cups so it doesn't "kick off" in the bigger cup.
 
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