The top coloured layers of paint are coming off fine with the scraping, and a light grey layer (assumed primer) below is coming off easily enough with hand sanding. Below these layers is a darker grey layer which is very hard and with a fair bit of elbow grease is not coming off. It is off in some small locations exposing the yellow fibreglass layer below. I know somewhere in these layers there is a gel coat, but I have got fairly confused about what this is and what it looks like from previous posts. I've added some photos below that will hopefully help.
My question is, do we need to remove this harder grey layer, down to the fibreglass to prep for a new paint job or is it fine to leave it and just take the surface down to the fibreglass for areas of repair?
To add to my confusion the doors do not have the same hard grey coat and the yellow fibreglass layer is easily exposed under the lighter grey layer.
Any help welcomed, I don't want to take it too far and add a load of unnecessary new work to fix it.
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The gel coat is a translucent, yellowish layer similar to looking at the fibreglass from the underside. A grey layer is a primer surfacer layer. I removed the paint from my car with a sharp, half inch chisel, get the angle right and you can strip the paint off quite quickly, especially if it's a thick layer. I found that the chisel cut through the primer layer as that was soft and I then sanded the remains off, easy because it is soft.
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There is a misinterpretation as to what gelcoat is. Gelcoat is the first application of resin to the inside of the mold. With the exception of the Bourne cars, which had a grey coloring added to the gelcoat, most early Lotus cars had a raw fiberglass look.
On fiberglass products where the glass is the final finish, a dye is added to the gelcoat to color it; these are items such as boats, some race car bodies, as well as other products, where painting is eliminated to save cost, or for lightening.
The gelcoat is sprayed or brushed into the mold, and it dries with a sticky uncured surface to which the structural glass filled polyester is bonded. The gelcoat dries hard next to the mold; it does not fully cure when exposed to the air. Gelcoat is brittle and is the cause for many of the surface cracks from damage or stress. When you repair these cracks you are usually grinding through the gelcoat.
Unless you are doing this job by hand to save money, I would suggest you look into soda blasting to remove the paint. It will not cut into the structure of the body, and will expose all surface damage which then can be repaired.
You can buy a small soda blaster from companies like Harbor Freight here in the U.S.; they are quite cheap, and the blast media is cheap also.
I have had experience with fiberglass as an engineer, and have done soda blasting, as well as having my S1 Elan blasted to remove the its paint.
Hope this helps.
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You can probably just take the paint down the the hard primer - if that is still nicely stuck to teh glass fibre there is little point in going any further. Your painter should be able to seal off the layer before he/she primes and top coats.
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Re-Face is an excellent first coat, after you get the lines smooth. Lots of cleaning spray gun as its a two-part exothermic.
I used an epoxy primer
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The only places I did not do that is where there was clearly body filler used on a poor surface. My Sprint is fairly late and I think the Lotus moulds were past their best by then - a LOT of pin holes near almost every edge for example!
Ref stripping I did most of it using a flap disc on an angle grinder although I would not recommend this since it was too aggressive in a number of places causing me to have to body fill some areas.
I tried a couple of paint stripper chemicals, but these were of limited effect.
However AFTER I had nearly finished I saw a You-Tube video of someone warming the paint and using a conventional paint scraper. This would have been even more effective if the scraper had been a PULL type since it would not have the tendency to dig in. You can buy ones with replaceable blades, but I have made a couple of these and they can be easily re-sharpened - let me know if you want a pic.
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Regarding the gel coat colour. My 1966 S2 definitely has a grey gel coat. The photos you've posted look very similar to mine, and the fact that you've identified a difference between the body and the doors It looks like you're body shell has a grey gel coat. One way you might be able to be more certain is to look at the underside of the car. Mine had only a very light over spray of colour on the underside and because there was no preparation of that surface for painting the over spray scrapped off very easily. If it's the same on yours you'll be able to see the gel coat colour in these areas. The picture shows the underside where the rear of the chassis locates (diff area).
Good luck with your paint stripping.
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