Tom,
Avoid woven materials in a cosmetic part, like the body of a car.
If you had start with a mold to create a new part, and put in several layers of matte first, then a layer of woven roving 2-3 layers deep, the weave pattern still eventually, over time, imprint it’s weave pattern through to the surface. Yup, 'tis true.
If you?re doing racecar body work, lightness and strength trump cosmetics, and a little weave pattern doesn?t matter. But if you?re making repairs to? or over-restoring a street car to ?show quality?, then you don?t want woven materials involved anywhere. Your best efforts will look good initially, but the weave will eventually imprint through. It may take a very discerning eye to pick up on it, but the fact that you’re already going down this road implies that you’re looking for a good surface finish… eliminate the weave.
Lotus used chopped strand (ie, like matte sprayed out of a gun) for a reason other than just expediency. They avoided woven fiberglass, and so should you.
Similarly, if you ?fix? stress cracks by applying a fine layer of tissue/ veil over the full body, the hidden cracks or flaws will eventually imprint through. Any crazed paint, stress cracks, repaired fractures, or obvious flaws must be properly repaired first? there?s no easy way around that. Then, and only then, a full overlay of ? oz tissue can be a good final step. But it should never be used as the first, easy step to hide flaws… they’ll just come back. Fix them correctly first, then apply your layer of finishing tissue to the now-smooth panel as a surfacing agent, using waxed polyester ‘Surfacing’ resin.
If you tissue/ veil the body, then to the extent possible, use one large piece to cover the entire surface in one shot. Clearly, you can?t cover the full body with one ?blanket?. But you can do doors, bonnet & boot lids, and major body area in large pieces of veil. That will avoid the need to sand down any overlapping edges between smaller panels. Don’t make life harder than it has to be.
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The original Elan/ Europa bodies were laid-up using polyester resin. Knowing the exact brand and grade won?t help you since now, ~50 years later, it won?t be available.
In a broad generalization, there are two basic types of polyester resin: 1) Laminating resin and 2) Surfacing resin (sometimes called Finishing resin. Polyester won?t fully cure in the presence of air? it needs to be sealed off. For that purpose, surfacing resin contains paraffin wax which floats to the surface, sealing the resin off from the air so it can cure.
But you don?t want wax between layers deep in a multi-layer laminate, so laminating resin contains no wax. Build-up multiple layers with laminating resin, then use surfacing resin for the last layer only. If you?re just resurfacing an old fiberglass part with a single layer of glass, then use surfacing/ finishing resin. However you get to that point, the last layer to go on must use surfacing resin.
If you know what you?re doing, and you?re good at it, there?s another option for external lay-ups (ie, on an existing body, not in a mold). Do all the wet lay-up/ repair work, including the last layer, with laminating resin, keeping the lay-up as dry as possible (excess resin just adds dead weight). Let it go to a ?green cure? state? firm, but with a tacky/ gooey surface. That?s as far as it will go without something to seal if off from the air. Then spray it (or, groan, brush it) with a polyester filler. That will seal the surface, promote a full cure, and provide a nice sandable surface to prep for paint. In the end, you?ll sand most of that off.
Vinylester is similar to polyester, stronger/ better, but different. Don?t mix them in a single part layup or repair. Polyester for boats & cars, vinylester for race cars and homebuilt aircraft.
Epoxy is a huge family of resins, and at the top of the family tree are resins that are superior in all aspects to polyester and vinylester. That?s the stuff that vacuum bagged, autoclaved exotic car and aircraft parts are made of.
However, each resin has a different chemical signature, and will react differently with the other resins, and with any finishing system/ paint that is applied over it. Pick one, and stick with it. Or, Lotus already made the choice for you, polyester, so use it for vintage Lotus repairs.
Epoxy will stick to polyester better than polyester will? so why not use it on a Lotus body?
Like weave imprinting, each resin type has it’s own color and chemistry signature that will eventually imprint through to the paint surface as well. The Type 14 Elite in white is a good example. The body was laid up in polyester, and the doors used epoxy. I’m not certain, but I believe the bonnet & boot lids were a third resin. A few years down the road, and a white (or any light color) car become a patchwork of shades of white by body part (epoxy doors gained a pink hue). The effect isn?t bad indoors, but it?s obvious in direct sunlight. For a black or dark color paint, it’s less of an issue. But for white and lighter colors, you need to be very careful about what resin you apply before painting. Pick one resin (Lotus already chose polyester for you), and stick with it.
If you want a structural repair as a priority (building a racer?), then a good epoxy is stronger, and actually bonds to polyester better than more polyester does. But, if you’re trying to put a quality paint job on the car, and surface cosmetics are a priority, then avoid adding patches of different resins to the body. The original Europa body was molded using polyester resin, so use a polyester resin for your repairs/ resurfacing.
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There’s a ‘sizing’, or binding agent added to fiberglass matte / tissue that holds all the loose fibers together prior to use. It also makes it a little stiff, like a starched shirt. The solvents that are a normal part of polyester and vinylester resins (mostly ketone or acetone) quickly attack that binder so that the matte / tissue becomes very limp and pliable during lay-up. Epoxy doesn’t contain such solvents, and it can be difficult to get matte to conform to convoluted shapes just after wetting it out with epoxy. But give it time to soak, and it will eventually soften and become pliable. If you’re using epoxy with matte / tissue, don’t mix a ‘hot’ batch that will cure quickly. Go with a slow cure to give the matte time to soften and follow the contours.
That’s important on a convoluted shape. On a broad, mostly flat surface like the bonnet, that’s not a big concern, but it’s still something to consider. And if you use polyester (as you should on a vintage Lotus body), it’s no problem at all.
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Paint doesn?t stick to paraffin wax, so it?s critical that the surface be thoroughly cleaned ?wax-free? before giving any thought to spraying on anything? filler, primer/ surfacer, paint? ?anything? that you want to stick.
Acetone, Ketone, MEK (methyl-ethyl ketone) and lacquer thinner are all effective at removing wax, finger prints, and any other smudges that might interfere with paint adhesion. However, they will also eat paint. All those solvents can wick down into the fiberglass, following any micro cracks, or even wicking in along exposed glass strands. If you paint over freshly solvent-wiped fiberglass, any trapped solvent will wick up to the surface and attack the paint from below. The result will be paint blisters, usually from small pimples to diameters the size of a quarter or half dollar. And they can cover the entire surface that you wiped-down prior to painting.
ANY use of chemical paint strippers or chemical solvent surface cleaners must be followed by a l-o-n-g rest period, preferably under a hot sun, to allow ALL traces of those chemicals to evaporate before applying paint. A ?long rest? can be a full day or several for ?hot? solvents to weeks for Zip-Strip or similar paint strippers.
I?m paranoid about using chemical paint strippers on fiberglass panels. IMHO, the best paint stripper is sand paper on a ?DA? or orbital sander? or a hand sanding block. Paint stripper is faster and easier, but fixing panel-wide blisters in a painted surface is much harder. Pick your poison.
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There is a paint flex additive that is mixed with paint that is to be applied over modern flexible bumper covers. Compared to full steel bodies, most… just about all of the vintage Lotus bodies flex enough to cause the paint to crack. It’s a good idea to use flex additive in all paint applied to a Lotus body.
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Off Topic, but…
A friend of mine used to own a Countach. The body was mostly metal, with a few graphite pieces mixed in… like the front bonnet. Over time, the weave would imprint through, and Countach fans consider the weave pattern a badge of honor… proof of the car’s originality. One time he had some body work done to the front… nothing that involved the bonnet. The body shop took it upon themselves to do him a favor while they were working on it, and ‘fix’ the bonnet. It came back looking like a mile deep black mirror. Perfection. Their hearts were in the right place, but they really ticked him off… he pissed & moaned that it would take years for any hint of that weave pattern to come back.
Regards,
Tim Engel
Sorry about the abuse of bandwidth.
