My 72 Europa SS

[gideon]

Or use epoxy resin if you want to bond to the foam.  It doesn't eat polystyrene like styrene does.  Surfboards are often made from a polystyrene foam core with an epoxy and glass skin.

[Sofa King]

The epoxy resin probably would have made this project much easier. I’m still learning the tricks of working with fiberglass, so every idea gets filed away for future use. One of my build philosophies has been “if you copy from one person, it’s plagerism, if you copy from everyone, it’s research!” I’ve done a lot of research!😂

[Yellowbelly]

Brown parcel tape also works well especially when given a coat of wax polish.

[TCS4605R]

The Lotus fiberglass is made with polyester resin, so I have always stayed with polyester for repairs.  I don’t remember what the compatibilities are between polyester and expoxy resins are - maybe some else can chime in here.

Tom
TCS - 4605R

[Sofa King]

All of the fiberglass work that I did on my car was done with polyester resin. The first primer layer was epoxy, then I used a polyester high build primer, before sealer and then paint. There were no reactions between the epoxy and polyester layers.
The foam that I used on the side skirts, is polystyrene, which does get eaten by the polyester resin, I believe due to the solvents in both being the same. You can use pvc foam or polyurethane foams with polyester resins.
From what I have read surfboards are made with both polyurethane and polystyrene, but the latter is covered with epoxy first. Please correct me if I’m mistaken.

[gideon]

I prefer epoxy resin for fiberglass repairs.  It has better mechanical properties and it shrinks less when it cures.  The most important thing is that it sticks better.  It bonds to old polyester resin fiberglass better than polyester resin does, and it holds onto the the glass fibers better too.  So you get stronger repairs.  The downsides are:  i) price;  ii)  it's not original;  iii) it degrades with exposure to UV light (not a problem if painted); and iv) polyester resin may not bond well to epoxy - though it can be done if you know what you're doing.

I reckon the advantages of epoxy outweigh the negatives, but I know that not everyone who restores old fiberglass cars agrees. 

[Clifton]

For what it's worth on epoxy. I filled a lot of spider cracks with it. Looked great but when it gets hot in the sun, you can see them all. It expands at a different rate than polyester.

[gideon]

Clifton - what brand epoxy did you use? 

[Clifton]

I started with US Composites with their slow hardener. After I found it to be too soft when hot I called, they said the slow  is only good to 160 f. Then I bought Adtech 820 with medium. I think there's is good to 180 f.. Still no good.  In Phoenix, a white car will get 160 easily in the sun. I checked with an infrared thermometer. When it get's brought back into the garage and cools down, they all go away.  At least the car is white.

[gideon]

Clifton, thank you for letting us know about the star cracks.  I hadn't heard about that problem before. 

[gideon]

I found a table of coefficients of linear thermal expansion online

https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

The relevant lines from this table are

Epoxy, cast resins & compounds, unfilled   45 - 65
Epoxy - glass fiber reinforced                   36
Polyester                                                   124
Polyester - glass fiber-reinforced                   25

(units are 10^-6/K)

So the addition of glass fibers makes a huge difference to the thermal expansion for polyester and a smaller, but significant difference for epoxy.  I'm thinking that for filling (relatively) deep cracks the addition of some glass fibers to the mix would reduce thermal expansion differences, which might make the whole visible-spider-crack-in-hot-sun thing less visible.  This is the kind of fiber additive I was thinking of

https://www.jamestowndistributors.com/userportal/show_product.do?pid=97692

[Clifton]

So the addition of glass fibers makes a huge difference to the thermal expansion for polyester and a smaller, but significant difference for epoxy.  I'm thinking that for filling (relatively) deep cracks the addition of some glass fibers to the mix would reduce thermal expansion differences, which might make the whole visible-spider-crack-in-hot-sun thing less visible.  This is the kind of fiber additive I was thinking of

https://www.jamestowndistributors.com/userportal/show_product.do?pid=97692

I used milled fiber with some cabosil for thickener. I used it on the doors repairs too but with polyester resin and they are perfect.

[Sofa King]

I’m not familiar with Cabosil, but I have used Duraglas and angel hair or cat hair with good success.

[Sofa King]

I just saw a post from Lotus Joe that reminded me of the first thing that I ever “cut” on my V8 Europa project. Right after I bought the first donor car, a friend of mine gave me an article that he had cut out of a Car and Driver from 1972. It included the attached drawing! I made several photocopies of that drawing, and physically cut and taped the wheel openings back on using the background grid for scale, so that I could see how the car might look if I made the changes that I was envisioning. I liked what I saw, so down the rabbit hole I went!

[Sofa King]

The photo on top is closest to how the car was actually built.