Glass body Epoxy/GRP?

Ant · #1 (**permalink**) 11-08-2003, 08:08 PM

Seeking tips on bodywork, I have a basic GRP polyester resin type Cobra, and have done some repairs and alterations!

One repair about size of a hand, was performed with epoxy resin and woven cloth on the side/turnunder of a rear mudguard etc, after it split due to muggins doing an incorrect purchase point, body lift off, and it stuck on chassis while using an endless chain, and not levering jam properly.

I have read where epoxy and polyester have different expansion rates when subjected to hot sun, and the result can be material print through, especially when using Black or dark BRG paint!

I used epoxy because I thought it would be stronger, as the repair is a secondary bond, I intend on using chopped cloth on the outside to avoid the potential print through of say woven materials, but may need to look at other fillers etc. I have looked up West Systems and Fibre Glast developments and other websites and have found nothing on this, maybe I am concerned over nothing.

IS THIS AN ISSUE WITH AN EPOXY REPAIR ON GRP BODY, AND CAN THIS POTENTIAL PROBLEM BE AVOIDED WITH CORRECT SURFACE FILLERS/UNDERCOATS/PAINT?

mikeinatlanta · #2 (**permalink**) 11-09-2003, 01:16 AM

Expansion rate have more to do with the fiber than the resin. I am experienced in composites but not glass cars. I wouldn't expect it to be a problem.

Rebel1 · #3 (**permalink**) 11-09-2003, 04:22 AM

Hi Ant..you wont have a problem with the epoxy and the woven cloth, but you will have a problem with the chopped strand mat. Chopped strand mat is held together with a binder which dissolves in polyester, but wont dissolve in epoxy. There are special chopped strand mats available for epoxies but hard to get in small amounts.

I would recommend you visit a custom boatbuilder and get a small amount of a heavy fiberglass cloth. (maybe the cloth you currently have will do). Cloth does not use a binder. Pull the cloth to pieces so you end up with lengths of the glass welt, (like small rope) then cut that into short lengths and fluff it up into loose glass fibers. Mix this glass with your epoxy resin to a gooey fibrous mess. then apply as you would a putty to just under the finished surface. Before it hardens completely(can still mark it with a fingerprint) apply the same resin ( but no glass) mixed with talc or microballoons as a final filler...sand it next day.

Epoxy has a significantly higher secondary bond than polyester and is somewhat more flexible. It is not normally used in a repair situation you described. Generally, because of the need to keep all body surfaces expanding at similiar amounts.

However, as a high quality surfacing compound, it is unsurpassed. ( again, because of its higher secondary bond strength and flexibility.

Hope it works out for you.

Ant · #4 (**permalink**) 11-09-2003, 03:50 PM

Mikeinatlanta,

Expansion rates etc, I could probably grind all the epoxy repair and do in polyester, it would result in a much bigger repair area?

I spoke to my car body man, he suggested a good quality body filler over the top like Epifill and such like, if it came through they would address it then!

Rebel 1, you make good sense, as above I wish I had done the repairs in polyester, I built up a flange inside the trunk with epoxy and woven cloth probably 7 layers thick, but I used normal binder matt in the middle layer to take up a bit of room, mind you its all glued and not a structure, one layer hopefully wont make any difference!

One thing about this I will be more aware of material compatibility and not so good way to do things.

Rebel1 · #5 (**permalink**) 11-09-2003, 08:46 PM

Hi Again Ant, You lazy bu$$a....Epifill is just Epiglass HT9000 epoxy resin and some filler powders and some pigments....Mix ya own..much cheaper.

The epoxy repair you did wont show thru if you cover with either the Epifill or your own mix.....but....do put a layer of random mat (as I described) .. between the cloth and whatever filler you use. Will add some strength and give extra insurance against print through.

Dont get me wrong...the epoxy is the best repair in normal circumstances, however, our bodies are non-structural, therefore little load is placed on the actual body moulding.

Our preferance is for the body to stay fair and straight when it gets hot in the sun. A lot of this depends on how the body is moulded and what hard points are glassed in...ie. where the firewall/footboxes are glassed to the inside of the body.

All filling on my body has been done in epoxy...thats surface filling...not structural buildups. If I repair say the hole you made..I would use polyester to repair the hole...but would use an Epoxy filler (Epifill) for final filling after the repair cured proper.

I have a couple of mates with cobras who filled with polyester fillers (car bog essentially) and the fillers shrank over time with disasterous effects on the expensive paintwork....or it simply fell out because the amount of filler was excessive.

Tis not funny to hit a bump and have the filler fall out of ya door

Ant · #6 (**permalink**) 11-09-2003, 09:24 PM

Rebel1,
I have done other repairs in the door jam area with epoxy and cloth, then used Epiglass HT450 powder and epoxy resin to finish as a filler and fairing medium, Is that similar to Epifill?

This repair is the only external one, and there wont be any more done in epoxy! Regarding the random cut cloth, 1/16" or a bit more should be heaps to cover any woven cloth eh?

On my first Cobra I glassed using only Polyester in very cold conditions poor quality control, and ten years plus later its still looks good when I visited the current owner recently - how did that happen!!!.
This bloody car I am so fussy on conditions and body preparation but got blinded with the additional bonding capabilities of epoxy and tried to change to using epoxy only.

As mentioned in a previous post (my excessive ramblings) I can quite easily cut out the epoxy area taper out another couple of inches, and I am still only yikes halfway up the mudguard, one lives and learns if I left it alone all it needed initially was a very small repair.

Rebel1 · #7 (**permalink**) 11-10-2003, 03:17 AM

Yep Ant...thats the stuff...HT450 mixed with 9000 resin gives you as near as damn it to Epifill. Epifill does have white pigments to make it white white or they also do timber colours.

The 9000/450 mix might go off white as it cures but that is just cosmetic and has no bearing on the strength. If you want it brilliant white...put a little pigment in it.

1/16 of milled glass mix over the cloth would be just right ...followed by straight epifil or 9000/HT450 mix would be just the ticket to get it all fair and smooth....apply the Epifil/450 mix before the random glass mix has cured .

Wont shrink, is compatible with all paint finishes, is totally waterproof, and when mixed with milled class fibres, is immensly strong...you would destroy a polyester laminate before that stuff lets go.

But...a little of an overkill for a polyester body.

Damn good stuff...sticks like NZ sheep dung to a woollen jumper.

OOpsy...couldn't help myself

Ant · #8 (**permalink**) 11-10-2003, 10:19 AM

Rebel1

Thanks mate for your experience in this area most helpfull, I guess its what you can get away with, and yep youre right about the sheep dung!

Hey the big game is on this weekend, Aussie doesn't look as good on paper but they could still pull one out of the bag!

Rebel1 · #9 (**permalink**) 11-11-2003, 05:42 AM

Ant...Ant..Ant

Love ya confidence about the weekend ...but...I'll wait till the game's over mate, then you're gonna cop it

And..to make it easy for ya...we're not even gonna change the team

Rebel1 · #10 (**permalink**) 11-15-2003, 04:13 AM

Guess you were right Ant...we pulled it out of the bag

WooHoooo!!

Ant · #11 (**permalink**) 11-15-2003, 05:08 AM

Congratulations and you deserved it, we just didn't have the hunger, speed, and appeared flat and slow!

Rebel1 · #12 (**permalink**) 11-15-2003, 05:16 AM

Ant, I gotta agree ... I expected more of the NZ side.

I really was looking forward to a closer encounter.

But then again, had we not won..I would have been mighty pi$$ed off

750hp · #13 (**permalink**) 11-15-2003, 06:24 AM

You've gotta love it when the 4:1 underdogs get up and win !!!!!

Never mind that the only try we scored was from an intercept

Ant · #14 (**permalink**) 11-15-2003, 04:14 PM

NZ has a habit of thinking we have got the best team and the

sack the coach and some of the management team!

All the skill we have where did it go? your passing, defence were excellent. I hope the guy that got injured in the scrum and went off on the golf cart is okay.

Ant · #15 (**permalink**) 11-15-2003, 04:31 PM

Further to that (her indoors) is from Bournemouth UK, and strongly supportive of the english rose, so will see what happens tonight!

I reckon though the poms will be meeting the all blacks in the play off!

Ant · #16 (**permalink**) 11-15-2003, 05:51 PM

Rebel1,

I applied some heat by a small fan heater on low, on the mudguard lay up, after it had gone from its liquid stage , after heating about 20 minutes, I went out to the shed, and could hold my hand on the job, it was reasonably warm, not hot.

How much heat can epoxy take?
I have the right hardener and temperature, but sometimes get impatient when the cure appeared to be going a bit slow

Rebel1 · #17 (**permalink**) 11-16-2003, 04:57 AM

Hi Ant...Epoxy to me is an over night cure.. but depends on which hardener your using. I hope you mixed it 2:1 ratio.

Nice warm days in Brissy (over 25) will cure in maybe 6 hours

This ratio is imperative..no more..no less...the more hardener does not guarantee a quicker cure. The key to a quick cure is to use a fast hardener and to leave the mix for a while before using.

Epoxy can take a heap of heat...not sure exactly how much but lets just say it is at the top of the resin tree. ie. It is the most stable of the resins.

The reason I used it for surfacing work rather than polyester filler is that epoxy does not shrink and has that much higher secondary bond strength. Further more, it is more flexible than the polyester so it will conform to the rest of the body. The body I have is not what I call a "good moulding", needed a heap of filling to make fair.

I hope your epoxy has gone off by the time you read this.

Ant · #18 (**permalink**) 11-16-2003, 12:54 PM

Thanks, will leave it for a few days and should be excellent!

I use pumps which measure correct ratio!

The G Force T5, have you used it yet, and did you get it in Aus?
I am interested in a decent gearbox, had a Seanz racing box in other cobra I sold, but have been contemplating a new Richmond five speed for this one!

Rebel1 · #19 (**permalink**) 11-16-2003, 06:53 PM

Hi Again Ant, Re gearbox

I know my sig line states I have the G-force T5 but as yet it is yet to be modified. I currently have a brand new 7003A WC T5. I purchased that some time ago when I was planning to use a 302/331 stroker.

However, I have since decided to use a 351 based stroker and of course the T5 is just not up to that task. I am also reluctant to invest in a tremec as I just dont like the first gear ratio, and besides, I already have the T5 and would prefer to use it if I can be convinced it will take the power of the 392 stroker.

I have emailed g-force and on what they tell me it will be reliable with their kit. I have also emailed:

http://www.5speeds.com/

They modify T5's using the gforce kit and a 5th speed bearing modification they supply and they also confirm the box will be reliable with the 392 stroker.

I am currently waiting the release of a .82 overdrive ratio for the Gforce kit. When that is available, I'll make a final decision.

Cheers

grumpy · #20 (**permalink**) 11-17-2003, 12:44 AM

Ant,
It's the same in the world of composites as elsewhere, why mix unlike components. If you do you will possibly suffer the consequences.
The finest material going in every day auto body composite materials, is simple polyester gelcoat surfacing and isothalic polyester resin with woven roving.
Why use vinylester, while it's cheaper than iso, it has different properties and so does the epoxies. While all of these resins will stick to anything, they will not bond to each other necessarily.
grumpy