Thread: How to Work Fiberglass Right

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Originally Posted by 36 sedan

My tin skills are poor, this has compound curves. I'm afraid I've wasted more on tin already than I could have made it from fiberglas.

Do I need to make a reverse mold out of plaster first, or can I lay over the plastic lid?

Are there other materials besides fiberglas I should be looking into to make this from?

If you've got a good fit with the plastic lid, and if you can accept that the fiberglass piece is going to be slightly bigger since it's laid on top of the fitting part, then simply wax the plastic with a good coat of wax and lay the glass mat on top. Let it cook off for an hour or so and it will pop off easily and you can then sand it smooth, hit it with a coat of filler and it's done.

Thank you, exactly what I was looking for!

Originally Posted by shine

chopper gun or hand laid means nothing. type of resin is all that counts. there are many different tiers of resins. just like paint there is good better and best with 50 qualities in each. epoxy is the upper tier, vinylester then polyesters. i use epoxy resin for any repairs , vinylester for any mold work , polyester for things like speaker boxes and such. the key to resin work is cure. best way is to wrap in black plastic and set in the sun for a while. exposed to higher temps than normal.

Shine,,I know you have had experience with glass,too,,as has Pat.. We all have different methods,and different ways of approaching things with this stuff.. I was taught in the late 70's,by one of the better guys in the industry,,who did his apprenticeship in a boat factory..He went on to become a leading light in boat repair in West Auckland,,and was actually known by many,as the pox doctor,,cos of his experience in repairing polyester yacht hulls,,some of which had spent a year or two in the tropics..Anyway,, my forte has been,for several years,repairing a lot of automotive parts,,including SMC truck fronts,and bumpers,,and the regular fibreglass truck hoods,,from Kenworth,Mack,Freightliner,etc.. All of my work is done with polyester..I have no problem with it,,and I would prefer to do my repairs,,where possible,with what was used originally.. I have a few dirty tricks up my sleeve,for SMC,,and while it's not 100% foolproof,,they still last..
I use polyester for making molds,,with a good vinylester tooling gelcoat.. As a rule,,I don't even have epoxy in the shop,,but do get tired of grinding out crappy epoxy repairs,from inside some panels laid up in poly... ,,that look like they have been whacked in with a mop,and 4 times more resin than necessary..
I usually set my layups off with an infra red lamp,then leave them to finish.. most of my stuff,that I do in my molds,stays in the mold for two days,or so before I pull them.. Hey,,the black plastic works well,too.. have speeded up the mold curing with that method..
Gunna leave it at that,cos I don't think we need to have too many disagreements in this issue.. One of the reasons I hang back from these threads,,is,that you can guarantee there will be a few differences of opinion..
Gotta say though,,most of the chopper gun layups I have seen,,are either good,,or real bad,,such as the Deco Rides Lincoln Zephyr bodies..Ya need an experienced operator,with his mind on the job,,and a good guy on the roller to finish..

Originally Posted by rspears

If you've got a good fit with the plastic lid, and if you can accept that the fiberglass piece is going to be slightly bigger since it's laid on top of the fitting part, then simply wax the plastic with a good coat of wax and lay the glass mat on top. Let it cook off for an hour or so and it will pop off easily and you can then sand it smooth, hit it with a coat of filler and it's done.

There is no reason,for a fiberglass piece to be larger,Roger,,since a mold is usually taken off the outside surface of that part..If you take a mold from that part,,what comes out of the mold will be the same..... Unless,of course,that the plug is taken out of the mold,,before the mold has finished curing,,in which case,,the mold will shrink slightly..And,,it is very hard to take a mold off a thin plastic item,,or,,as I call it,,a ''street weight'' fiber item..They need to be braced well,,and build the mold slowly,,a couple of layers of glass at a time.. AND,,,DON'T use too much gelcoat in the mold,,as if it's too thick,,it will shrink from the mold as it dries..
For a small item,,I will make my mold about 3mm thick,,built up over a couple of days,and a week of curing..minimum..

done more fixes with polyester it worked . cost as not has much as the epoxy but it has its place . over the years working with smc i used siwss polyester gell for smc for the big semi flip fronts ends re built many with the gell . many times i was the guy that took the part raw and did finish work to paint with no gell coat on the air plane stuff . last time i was close to a boat repair i did not even work on the damn thing i started getting cold and breaking out.i found out the epoxy i can not be in the same shop with epoxy dust. most repair job were someone did not do a good fix were guys think slopping on to much resin with no mat or cloth

Originally Posted by lamin8r

There is no reason,for a fiberglass piece to be larger,Roger,,since a mold is usually taken off the outside surface of that part..If you take a mold from that part,,what comes out of the mold will be the same..... Unless,of course,that the plug is taken out of the mold,,before the mold has finished curing,,in which case,,the mold will shrink slightly..And,,it is very hard to take a mold off a thin plastic item,,or,,as I call it,,a ''street weight'' fiber item..They need to be braced well,,and build the mold slowly,,a couple of layers of glass at a time.. AND,,,DON'T use too much gelcoat in the mold,,as if it's too thick,,it will shrink from the mold as it dries..
For a small item,,I will make my mold about 3mm thick,,built up over a couple of days,and a week of curing..minimum..

See, there's the reason for the question as you jumped right to taking the part that fits and making a mold of it, while my inexperience pointed me to simply using the piece that fit as the mold, making a fiberglass over lay of the part, popping it loose and then working it to finish. Your method is right, taking time to make a mold from the part, built up slowly and maybe even sticking on some ribs for bracing it straight, and then being able to make multiple identical parts out of that mold with a gel goat finish, too.

Originally Posted by pat mccarthy

done more fixes with polyester it worked . cost as not has much as the epoxy but it has its place . over the years working with smc i used siwss polyester gell for smc for the big semi flip fronts ends re built many with the gell . many times i was the guy that took the part raw and did finish work to paint with no gell coat on the air plane stuff . last time i was close to a boat repair i did not even work on the damn thing i started getting cold and breaking out.i found out the epoxy i can not be in the same shop with epoxy dust. most repair job were someone did not do a good fix were guys think slopping on to much resin with no mat or cloth

Thankfully,Pat,,the only boat repairs I've had anything to do with,,are polyester layups,,and not GOP,with epoxy..In fact,,i do very little in the boat side of things..We have enough boat repairers in the area to take care of them.. I have a problem with people who come to me,wanting me to fix their broken junk,,and expecting me to do it for very little,,and the parts have been damaged and repaired badly in the past,,and can't see that it usually means more work,,by going down deep in the repair,,and starting with a clean slate,,so to speak,,instead of just slapping more junk on top..

Originally Posted by rspears

See, there's the reason for the question as you jumped right to taking the part that fits and making a mold of it, while my inexperience pointed me to simply using the piece that fit as the mold, making a fiberglass over lay of the part, popping it loose and then working it to finish. Your method is right, taking time to make a mold from the part, built up slowly and maybe even sticking on some ribs for bracing it straight, and then being able to make multiple identical parts out of that mold with a gel goat finish, too.

I usually look at a mold,as an ongoing item,Roger,unless it's a strictly one off,,which will then only get the minimum requirements.. All my molds are about 5mm thick,,for the auto parts,,coremat on any flat surfaces,in the last few layers,,that is,,under the top layer of glass,,and a piece of 1/4inch mild steel rod around the edges of the mold,to keep the shape.. Over the last ten years,,the molds we bought,have had a check over for fit,etc,,and usually a new part has been developed,,prepped,,painted,,and molded..Our T bucket mold has had 33 bodies out of it now,and requires minimum maintenance..

Originally Posted by lamin8r

Thankfully,Pat,,the only boat repairs I've had anything to do with,,are polyester layups,,and not GOP,with epoxy..In fact,,i do very little in the boat side of things..We have enough boat repairers in the area to take care of them.. I have a problem with people who come to me,wanting me to fix their broken junk,,and expecting me to do it for very little,,and the parts have been damaged and repaired badly in the past,,and can't see that it usually means more work,,by going down deep in the repair,,and starting with a clean slate,,so to speak,,instead of just slapping more junk on top..

when i was at the boat yard i never did any glass work. the glass shop was at the very end of the boat yard them guys would do the small fix were the boat was many times i was working on the boat to .seen them fix some nasty stuff we drop off boats many times for fixing in glass shop .i knew i lost brain cell s in that place. i think they kill flys with MEK . jon did the air plane a cars and race boats so the boats were wood then with cloth over the wood so the glass was not flying around the shop less it was a fix were you had to get to the wood and strip back paint for good bond with 8inch pad

MEK was band from our plant. They used it as a solvent for inks. when they used it they had to have a in plant fireman and truck at the job. realy bad stuff. Right up there with Triclorethyline .

AT THE AIR LINE S back in the 60s we used tri clor for washing parts---solvent tanks everywhere in the shop and hangers

Originally Posted by cffisher

MEK was band from our plant. They used it as a solvent for inks. when they used it they had to have a in plant fireman and truck at the job. realy bad stuff. Right up there with Triclorethyline .

yep love the smell of all of it to a point its right up there with nitro. and good race fuel that de icer for them planes sounds lke hot stuff must be alot of hot land /ground water by some of them air ports

MEK melted my plastic lid before I could apply the cloth or resin. Keep this up and I'll try painting next.........

Originally Posted by jerry clayton

AT THE AIR LINE S back in the 60s we used tri clor for washing parts---solvent tanks everywhere in the shop and hangers

McDonnell Douglas used it to clean interior panels and just about everything else until, 69, I believe, when some idiot dropped a smoldering rag behind the aft galley in a DC 8 that was ready for delivery. That caused quite a fire that delayed delivery for 6 months or so. That crap will turn your skin white, nasty stuff.

DC 8s were pretty much done about then---DC 10 and B747 and Convair 990 were becoming biggies with the B737 coming along in late 1968? I was in class on 37 in March 69 and a lot of the upper training people and flight management dept were starting to do dc10 and 47 stuff-----


I remember when I was still a ground mech working on a electrical problem in the dash of a food truck and got to feeling woosy---there was a open bucket/and rags under the drivers seat of tri clor-------