We're now in Cumbria, a few days into a two week holiday visiting the North of England and Scotland. In the run up to the trip, I attended to a couple of the growing list of repairs which Jim needs doing.
For a few years water has been getting into the back nearside corner of the cladding on Jim. Over time it has completely rotted through the plywood. I have known about it for a while but haven't had the motivation to deal with it. The damage has happened because one of the stainless steel capping pieces has started to separate from the truck body, and water has got behind the plywood.
The thin GRP skin is the only thing left in that corner, the plywood behind it had rotten away completely. The hole you can see in the photo is from me inadvertently sticking my finger through it when trying to ascertain how bad the damage was.
A few other corner trim pieces are loose and I will have to deal with these quickly so that the damage does not get as extensive as this section. I started by pulling away at the rotten wood to see how far the damage spread. Getting to this point took nothing more than a gentle tug with my hand.
Next I set up a series of guides/fences for the router. The first was for routing a 3mm rebate that would allow me to sheath the whole repaired area in a couple of layers of fibreglass cloth, without it sticking proud of the surface. Screwing router fence battens into good GRP seemed fairly brutal, but it was the only secure way of making a neat cutout, and I had to fill and sand the repaired area anyway.
Next I cutout the rotten plywood completely and rebated the edge to allow the new plywood to be dropped in place with a wide scarf type joint. The cutout was made using my Festool plunge saw and guide rail.
Before I could start with the repair, I wanted to make sure that water could not get back into the area so easily in the future. I cleaned all of the metalwork up with a wire wheel on an angle grinder, painted it with a couple of coats of Bratho Korrux, and resealed the sound plywood to the metal frame with a thick bead of Sikaflex 221. Cleaning rusty steel with a wire wheel is no fun, but it's a good way of getting back to clean metal, and without doing this step, there is no way the Sikaflex would make a lasting seal.
The repair piece was cut to the dimensions of the cutout from a piece of decent plywood, and coated on the edges and back with two coats of epoxy resin to help it in the event that water gets back into this area. I bonded it in place using West Systems epoxy resin which I thickened with microfibres, and held it in place with screws. I later removed the screws and filled the holes with more resin.
The piece that I cut for the repair was not a perfect fit, an I used epoxy resin thickened with microballoons to fill the gaps resulting from my poor measuring.
Next job was to cover the whole repair in a couple of layers of fibreglass. I had enough heavy biaxial cloth left from a previous job which to do the job. This tied the new plywood into the old, and provided a tougher surface than I could have achieved with painted plywood. I wet the surface of the plywood out with resin, pushed the cloth into the wet resin, and wet it out thoroughly using a small roller. I held it in place until it was gelling with gaffa tape. Once the resin had started to kick, I easily trimmed the excess with a Stanley knife.
After the first layer of heavy biaxial cloth layer, I laid another of finer twill weave. After this second layer, there was not enough depth left in some areas to apply another layer without it sticking proud of the surrounding wood. Sanding fiberglass is a lot less fun than sanding filler, and so at this point I stopped with the fiberglass and built up the remaining depth with thickened epoxy.
I had to put a decent layer of filler on, but I was still glad to have avoided sanding back fibreglass. I used epoxy resin thickened with microballons as a fairing filler. Car bodywork type bondo filler is quicker to set, and easier to sand, but it is not as durable, and doesn't adhere well to epoxy resin. There's no easy way to sand epoxy, even if it is thickened with lightweight filler; if you sand it too early it clogs the paper, if you wait until it has fully cured it blunts the paper remarkably quickly. I experimented with the random orbit sander to fair the area, but I was going through expensive discs too quickly. Using 40 grit paper on a hand sanding board ended up being the quickest method. As long as I changed the paper frequently it munched through the filler in short order.
After fairing the area to 40 grit by hand, I took it to 80 grit with the random orbit sander, and applied a thick coat of epoxy resin to seal the area.
After keying the resin coat to 80 grit with the random orbit sander, I cleaned the areas throroughly and applied a couple of coats of International pre-kote primer. I must admit that I failed to mix the microballoons thoroughly enough into the epoxy resin, and was left with some pinholes in the surface. Using epoxy as a filler is a pain as it takes so long to cure, and so I used a tiny quantity of bondo between the primer layers to fill the pinholes
Finally, I applied a coat of Rustoleum Combicolor with a roller. When I have time I will flat this back with some wet and dry and apply a couple more coats. This basic enamel is easy to apply, but it takes a long time to fully harden between coats. The colour match to the previous paint job is pretty good and with some careful polishing the repair should blend in well.
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