Fibreglass Spoiler Repair - Need advice.

Verell-

Don't know if this will help, but give it a look-see.

http://www.fibreglast.com/contentpages-Learning-Center-123.html

 

http://www.ferrarichat.com/forum/showthread.php?p=135062343

 

Make sure you use epoxy resin if you end up fixing the spoiler yourself with fiberglass. If you're near a good boatyard, they should be able to do a good job fixing it properly. I do not think that many bodyshops know what they're doing when it comes to fiberglass repair. If you neede more advice, please ask - we do this all the time.

 

Its a shame you are not close by, I would show you how to do it, all GRP work is quite simple but to write it down is very difficult.
You need to know if its made from polyester or epoxy glass fibre.
You can not mix the two, its more than likely polyester.
The thing that people do not like is the dust.

The cracking is in the gell coat, the only way to stop this is to sand it back untill you are down to the glassfibre, you can then fill with filler. If you don't they will return. You must repair the spoiler first!!!!

Your best way is to work from the inside out.
sand the inner spoiler off so you have no shinney surface left, clean off all the dust. You can then position the outside correctly (broken bits, cracks with masking tape on the outside) this will come off after all sets. lay up "inside" with a minium of three sheets of matting at repair area, with a larger sheet covering the whole repair.
After an hour or so you can remove all tape, start your sanding and repairing of the outside.
The whole thing will now be strong, but it will not be fully cured for a couple of days.
See what I mean about putting it into words!!!

the rest is just shape prep and painting, but thats another story.

Hope this helps

Mark...

 

Use cloth - it's stronger, and chopped strand mat is not really compatible with epoxy resin. The mat is held together by a binder that dissolves in stryene, the solvent in polyester resin. Epoxy doesn't dissolve this. Cloth is free of these binders. I'd go +/- 45 degrees across the crack, but you will likely remove so much thickness sanding the "V" area over the crack to apply the repair cloth that it does not really matter. Try alternating plies - 0/90 and -45/+45, building up thickness with a couple plies of each.

I think the overall repair strategy you outlined above is fine, but the hole drilling is not needed. Standard aviation practice for stopping crack growth on metal parts is replacing the part. On composite flight surfaces, the entire damaged area is removed, so there's no crack left to drill a hole into. I know what he's thinking of - like drilling a hole at the vertex of an angle cut into sheetmetal to eliminate the hard angle and prevent cracks from beginning, and I've heard of "stopping" a crack by drilling holes in metal parts, but the advisability of this is another topic entirely. Composites are fundamentally different from metals in the way cracks form, grow and stop. Just get rid of the damaged material and build up a fresh repaired area.

Go for the epoxy from the boat place - any retail boat store should have it too. Epoxy repairs are tougher and stronger than polyester (fiberglass resin) repairs, and the materials are a lot less smelly. Wear gloves and goggles and use a respirator, especially while grinding or sanding.

 

A "peel ply" on the surface will help - ideally you'd apply some clamping force. We use vacuum bags for this purpose. Clamping a thin board or something that will conform to the shape over the repair will work, too. Put a release layer like peel ply or polyethlene film over the repair first. The backside of the part can be bulked up, too.

If the part is 1/8" 20year old chopped strand polyester/glass, removing damaged material and replacing it with fresh woven glass/epoxy will probably result in superior strength to the original, even without bulking the backside.

 

If you pour some resin/fiber mix down the recess behind the spoiler from the backside, it greatly increases the strength of the spoiler lip itself. I did this on my last fix, and while it did add some weight, the lower spoiler lip is now very crack resistant.

Good luck Verell.

Spang

 

Verell,

Well I guess I'm a bit of a dissenter on this issue. I prefer polyester resin and matt for a repair like this and here's why.

The original piece was most likely made of polyester resin. I've done repair on my spoiler and it came out perfectly and remains so. I find it easier to use ployester resin and it provides adaquate strength. Epoxy is more expensive but provides some additional strength, but it's real advantage, especially in marine applications, is it's impervious to water when the film thickness is adaquate. These are not essential requirements for your repair. If the piece was in constant contact with water, I might elect to use epoxy.

The strength of a repair is primarily in the glass fibers as I'm sure you know. The resin merely bonds the the fibers together. Need to increase strenght? Increase the glass to resin content by laying down another layer or two of glass and squeeze out some of the unnecessary resin prior to the cure process. A light wooden strip, separated from the resin with wax paper, and clamped with some C-clamps, vise grips, weight, or whatever, works pretty well. Peel off the wax paper and clean off the residual wax with prep solvent, prior to grinding the repair down to the level of the surrounding material. I use a right angle die grinder with a Roloc disc or an oval carbide burr to remove excess material. Finish off by block sanding, primer surfacer, block sand again, then finish coat.

A down side of epoxy is that while epoxy can be used over polyester, polyester cannot be used over epoxy.

How much strength do you need? Under normal circumstances not much for the spoiler. If you hit a curb or speed bump again, neither polyester nor epoxy is going to help much. At best, it'll just fracture in a different area.

Why use matt? Well, it conforms better to curves and after cure and ageing is less likely to show a weave. I think it also wets out better.

Standard repair practice is to cup both sides of the damaged area and lay up matt and resin on both sides, with sufficient thickness so the repair can be ground to the level of the surrounding, sound surfaces. It's interesting that over the years I developed this method but later found that Lotus wrote the book on this subject. If you ever get a chance to read one of their Elan shop manuals you'll see all the tricks. On the back side of the repair, you don't have to be quite as careful, but I still like to only lay down only enough resin/glass to do a quality repair.

If you insist on epoxy, West Systems makes a very good epoxy, the standard in the marine industry. You will also need their pump system to reliably mix the resin and hardener. The mix of epoxy and hardener is more critical than polyester and the cure produces a lot more heat.

For polyester resin, I like the finishing resin supplied by Jamestown distributors in RI. It's a fairly low viscosity resin that wets out well, yet does not run unduly. Their part number for a quart is FIB-553 and costs about $14/qt. It comes with 12 cc of MEKP, almost twice the hardener you need this time of year. I find about 0.4 cc of hardener produces a reasonable cure rate in my garage. I use a graduated plastic beaker to measure out the resin in small quantities like an ounce or two. I find a 1 cc diabetic syringe ok to to meter out 0.4 cc of hardener per ounce of resin, though the needle is so fine it takes a minute to fill the syringe with the necessary hardener. In CT, I can buy these syringes over the counter at some pharmacies for about $4 for maybe 10. They can be reused, but eventually the graduations get washed off by the hardener. Use more hardener if you want a faster cure or less if you want a longer pot life. Excess hardener promotes a slightly more flexible cured product while less hardener produces a slightly more brittle cured product. Kind of counter intuitive. The way a chemistry professor at UCONN explained it to me is the additinal hardner separates the resin molecules a little more, resulting in the increased flexibility. Anyway I would not try to fine tune it too much. If you find the cure taking a little to longer than your liking, warm the layup with a heat lamp.

I hope I haven't introduced too much controversy here but I've been working with this stuff on my Lotus and racing sailboat for a lot of years.

Bill

 

I have done a fair amount of fiberglass work and I concur with Bill's methods. I have not used epoxy, but here it works well. Had good luck with polyester resin on boats and my '69 Corvette. The mat would be my choice too. You can weave a layer of cloth between layers of mat, but I have seen adhesion problems and the weave showing through so I avoid it. It is important to squeeze all the excess resin-out. Saran wrap or dry cleaning bag material works good because you can clamp it then peal the Saran wrap off.
Polyester resin loves heat--it works well with a heat gun or lamp. You can cook it to about 150 deg and it will harden in about 10 minutes. They say that you need this type of heat to fully cure it. Have been told by Corvette folks that if the repair is not exposed to high heat it will likely move. Many polyester resin and primer users let their repairs sit in the hot sun for 90 days or so. Notice how long it takes the resin smell to leave a camper shell cap?

I would be careful about making the spoiler too strong. On my car there is a crack cause by the spoiler being too stiff and not flexing.

Good Luck,

Mark

 

Verell, I have some clamping tips - call me if you want and I'll explain.

The reason that epoxy should be used for a repair is that it is a much better adhesive than polyester. The water resistance thing doesn't really factor in here - it's a big plus in the boat world, though. Once polyester resin has cured, as it did over 20 years ago in Verell's case, new polyester will not chemically bond to it. A mechanical bond is the only hope you've got, but polyester shrinks a lot as it cures, so this mechanical bond is significanty compromised as soon as the repair cures. The bond is significantly stressed from the getgo. Even without taking the shrinkage into account, epoxies are in general better adhesves from other chemical standpoints.

West System is our repair epoxy of choice. They make great products, great REPAIR MANUALS, and have most if not all of the info published online. Polyester body filler sticks as well to a properly prepped epoxy surface as just about any other non-porus surface, but why not experiment with West System's own line of filler additives, which stick a lot better than bondo?

Typically, epoxy like west system is tougher than polyester, and will "give" more before delaminating. Use of woven cloth with epoxy results in a tough, resiliant, strong repair, that doesn't have to be especially stiff as long as you don't build up too much repair area. Polyester/chopped strand tends to be very stiff, but also brittle, especially at the original part/repair interface.

I do not think that good repair epoxy was around when '60's corvettes or lotuses were around, so they made do with the best primitive chemical technology that they had. Ignore obsolete repair strategies.

Do the right thing, use epoxy, prepare the surface properly (you could try solvent wiping and sandblasting the backside if it's hard to sand), and don't mix too much epoxy at once. It's an exothermic chemical reaction, it's hot outside, and the 205 and 206 hardeners are pretty fast as it is. The pumps are great - syringes work well for precise measuring, too.

If anyone reading this does decide to use polyester resin (it's good for part fabrication), just use the amount of catalyst recommended by the manufacturer. It's a catalyst, not an addition reaction component, and you just need enough to kick off the chemical reaction that has already been iniated at the resin plant. Variations within a small range will increase or decrease the speed of the chemical reaction, but any physical variations in the cured resin are indicative of overly lean or rich catalyst mix, and the lamiinate is probably no good. Too much hardener, for instance, will make the reaction progress too fast, causing excessive heat and microcracking, and a permanently weak part.

Chris

 

Excellent discussion guys and thanks for the vote of confidence Mark.

Verell,

The first pharmacy I tried wouldn't sell me syringes due to store policy, but offered me free oral medication syringes. I asked for ant they actually gave me 10, as I didn't know how they would hold up to the methel ethel ketone peroxide (MEKP) catalyst. When I looked at syringes closely, I could see that I would have trouble withdrawing hardener from the 12 cc bottle, so I went to another pharmacy, which allowed the sale of diabetic syringes without a perscription. The advantage of the needle is that it will reach into the fluid without having to immerse the tip of the body.

Syringes of all types seem to be readily available on ebay. Of particular interest are catheter tip syringes with an elongated and tapered large bore. I believe one could easily slip a flexible tube onto the end and withdraw resine from a quart or gallon container. They are readilly available in 30-140 cc capacities, so are appropriate for metering small to modest batches of unmixed resin.

In the past, I always used 15-drops of catalyst per ounce of resin as a starting point for polyester resin. For my latest perchase of resin, the mix ratio was specified in tea spoons per quart, not the usual volume units. The mix ratios at 70 F were:

slow gel: 20 minutes or more 1 teaspoon/QT which I calculated to be 1:193
medium gel: 15-20 minutes 2 teaspoons/QT 1:97
fast gel: 10 minutes 3 teaspoons/QT 1:64

My Marks Handbook says 1 oz = 6 teaspoons = 29.6 cc's
1 QT = 946.4 cc's

So for one once of resin, at a medium gel recipe, I get: 29.6/97=0.305 cc of catalyst.

I hope I did my math correctly, but the results worked ok.

The first batch I mixed up was to the medium gel ratio target of 0.30 cc's per oz. I actually metered out 0.32 cc's. The cure was on the slow side for my liking so I upped the next batch to between the medium and fast (0.46 cc's) target. I used 0.40 cc's of catalyst. The residual mixture was just starting to jell in the mixing cup as I finished the last of this small layup, so this was just about right.

The thing to remember is that a large batch will begin to gell quicker than a small batch, not only in the mixing cup, but also in the layup. Since I was only laying up 2-layers, the repair cure was a little slow, but I speeded it up with a heat lamp. Had I laid up more than 2-layers, then the repair cure would have been faster.

Bill

 

http://www.bobileff.com/cpg/displayimage.php?album=29&pos=0

a nice addition to any 348 or others.


Erik

 

I wish such an animal was available as a simple bolt-on for the 308 long front spoiler. I have some black HDPE (High Density Polyethylene Plastic) sheet that I've been meaning to make a template for and cut for that same purpose...

 

My trick was to swap to the US version.

 

This may be helpful...............

Granted it's for a TR, but may be of interest, check page 2 of this thread....

http://ferrarichat.com/forum/showthread.php?t=98940&page=2