Bodywork Update

It seems I've posted nothing for ages. I've hardly even taken advantage of the ghastly lock down, but I have done one or two things worth posting up. Mostly I've continued doing the bodywork.

First off, I started renovating the front wheel arches. They were in a pretty poor state and it was really touch and go as to whether I would junk them and just get new ones or fix them. I decided to fix them, but I still might just get new ones later. Its been that kind of year!

This is what they looked like to start with:

This is just the drivers side, but the passenger side was as bad. There was a poor repair where it looked like tyres had rubbed through, large sections of the reinforcing were blackened and split, the front edge was frayed and naturally, both were covered in star cracks. The bad patch was easy to grind off and repair, so I did that first. Next, I tackled the reinforcing that runs around the free edge. 

This looks like it's made of glassed over pith-wood sections. I imagine this provided support for the reinforcing lay-up, without adding weight. It seems that when the wheel arch had flexed it had cracked the reinforcing, then water had got in and the pith wood had rotted. When I ground out the bad reinforcing sections, the wood had turned to black dust! 

I couldn't locate a source of the wood in the sizes I needed, but  I found that lengths of rope would do, if I stacked them, two on the bottom and one on top, and then laid mat over the top. I glued them down with contact adhesive to keep them in place while I glassed over them.

I also repaired all the cutouts for the suspension so that I was left with a blank wheel arch to re-cut when I began re assembly. This one is tissued.

Another reason for keeping these arches was to use them as trial pieces for practicing re tissuing. Why? well, because after months of rubbing down and repairing the shell, I was still finding sneaky little  cracks and other issues with the gel coat and I was coming round to the idea that the only way I could be sure that rogue cracks don't reappear after the paint stage and ruin the job, was to resurface the whole car. Eugh(!).

This is the approach used by many restorers of classic fibreglass cars, but there is very little information out there on the details of how to do it. Most of the information on repair, relates to boat hulls, but boats are not typically painted afterwards and they aren't typically resurfaced either. Anyhow, rather than relate my frustrating failures, its probably better to just bullet point the things I learned:

1. Don't expect re tissuing to smooth out any imperfections; it just adds hours of rubbing down. Rub down to a good shape first. If you are over tissuing smooth gel coat, rough it up first with 40 or 60 grit. New resin adheres poorly to old.

2. I used pigmented lay-up resin,  to see when I was rubbing through the tissue back to the original glass. I used white because:

3. A mist coat of black rattle-can paint is a great help in ensuring you get an even surface. Also it shows up well over the white pigment.

4. When laying down the tissue, I found that using a brush with a stippling action tended to leave an uneven surface and occasionally rucked up the tissue, which is difficult to reposition when wet. Using a gentle "painting" action is an improvement, but using a solvent proof mini roller was a vast improvement in surface quality. There is a danger that the lay up is drier than with a brush though, so you need to be careful to use enough resin to wet out properly. You will probably have to stick to brushes on the complex shapes.

5. Try to minimise overlaps of tissue, they don't look much when wet, but rubbing back takes much longer than you might think. A good trick with the edges of tissue is to leave the 2 or 3 cm (1 inch or so) of the edge dry. You can then pull them away from the wetted, laid up tissue, whilst holding the wet tissue down with a roller or brush. This way the dry edge separates from the wet tissue, which feathers out.  It then blends in much better.

6. I used 40 or 60 grit paper to rub down the surface after the tissue. The tissue surface may look fine but it's usually not. Don't make the mistake of believing you can just over coat lumpy tissue with gel coat and it will be OK. It won't. Make sure you shape the tissue layer before you gel coat over it.

7. Gel coat. There are a few issues here. Gel coat is not intended to be applied to the finished surface. It is designed to be applied to the mould and covered in mat. Its thixotropic so that it adheres well to vertical surfaces but it won't flow out so if you use a brush it will leave a very lumpy surface. Finally, oxygen inhibits the polymerisation process so the surface layer will be less "set" than the rest, meaning that the top layer will remain slightly sticky

8. Because of the above, brush painting gel coat over the tissue isn't a good idea. Because its not designed to flow, you won't get a flat surface. You can try to thin it out with layup resin, but I've found that isn't very effective. The answer for me was to use gelcoat thinned out a bit with lay-up resin, laid on with a solvent resistant six inch, short pile roller. This will still give you a finely stippled surface but its relatively easy to rub back. The more professional approach is to use a spray gun intended to spray gel coat, which may well give a better surface finish. Theres a nifty one available that uses a disposable mixing cup as the reservoir HERE and the results look good.

9. Sticky surfaces: I found several solutions to this on the web:

(i) just leave it for a week or so and rub back with 60grit. Works for me. You need plenty of 60grit as it will clog, but once the surface was gone I found it was OK. The disadvantage is it needs lots of rubbing down, so make a lot of dust.

(ii) Use a wax additive such as this one. Its mixed in with the gel coat and floats to the top when applied. This apparently forms a barrier that prevents oxygen getting at the surface and so gives a tack free surface. I didn't use this approach as I was concerned about surface contamination with the wax, which might interfere with the paint. I couldn't find any information on this issue, so elected not to go there. I didn't want to find out whether it worked 5 years after I finished the car.

(iii) Over spray the applied gel coat with PVA. This apparently then dries to form a seal and can be wiped off when the gel coat is set. I haven't tried this yet but I will give it a go later and report back.

(iv) Overlay the gel coat with a plastic sheet when it is partly set and remove it when fully set. Hmmm, i tried this and the sheet stuck to the gel coat and when removed left odd waves, where the sheet wasn't quite flat. I also tried using cling film...... Just don't bother. Might work on a flat surface, but on compound curves this approach is hopeless.

Here are some pics:

Here is one of the wheel arches on gel coat. You can see the stippled surface and the effect of not paying attention to the edges of the sheets of tissue. While it all looks OK......

Heres what it looks like when flatted out......In this case the surface tissue was applied with a brush. It will need another two coats of gel coat.

Here is the passenger side door after two layers of tissue applied by roller.

and here after two coats of gelcoat applied by roller.

This shows the process of tissuing the passenger side forward of the door. 

Roof, might need another coat, but turned out nicely.