I did not get much work done on the boat during the week (nor did I last weekend or the days during the week before so it has been 2 weeks with not much done). I did manage to sand the inside of the roof to smooth off any sharp edges of glass. I will make a roof liner over the saloon and then coat the inside of the roof with the white epoxy. It will be more a sealer coat as it will be under the roof liner and not visible but I would like to give it one more coat of resin and then paint so this will be a good way to do both in one coat.
To make the roof liner I investigated a number of options including using nidacore, chop strand with polyester resin. I also thought about whether I should make it in one piece or not. I decided in the end to make the liner in 3 parts, the centre part out of nidacore the 2 outside parts out of filler core, light (200g) cloth each side and polyester resin. The reason for making it in 3 parts was that it would be much easier to upholster and also so that the liner could be taken out of the saloon if needed, a one piece could not be moved but a 3 part is no problem. The reason for using polyester resin is cost. It is about 1/5 the price of epoxy and there is not reason for the roof liner to be made from the superior epoxy. It will have no load on it, it just needs to be stiff, light and hold its shape. The filler core is to thicken out the liner and to separate the 2 layers of glass. I will make the 2 side parts out of glass and filler core but the middle part will be nidacore. This section is just a slightly curving section and not a compound (curving both fore and aft and side to side) curve like the sides. As can be seen from the first pic below, gravity alone is enough to get the nidacore to curve to shape. I have marked off one full sheet width for the nidacore and will make the side parts to fill the rest.
I started by cutting the various parts to shape and size, 2 layers of surfboard cloth for each side of the liners and the filler core. Filler core is a mat like material with holes in it to aid in wet out, it has no structural strength even when resin infused, it is only ever used to pad out glassing to make it thicker. It is easy to cut and wets out to a flexible filler so that it will form compound curves without bulging like a more rigid core like nidacore will. I then taped the roof with clear packing tape to provide a non stick surface for the wet out. Polyester will not stick to epoxy but can be mechanically bonded so you must line the roof with plastic and sticky tape is the best way to get the tape firmly to the surface shape of the female roof mold. In retrospect brown packing tape would have been easier to apply as the clear is sometimes difficult to see that you are overlapping the tape each strip but so long as you don’t miss any area it will be ok.
Taping these areas took nearly 2 hours! I cant believe where the time goes. Jo went to lunch with her mum and rang (yesterday) to say she was on her way back to pick me up and I said I needed more time, she reminded me of the time. It was already 5pm and I had been working all day and not noticed it fly by. So I had everything ready for glassing but not enough time left in the day to do the wet out. It would have to wait for Sunday.
So today I did my usual early start, it helps with such work as wet outs because the shed has not had the days heat on it to warm it to the sauna it is past about noon each day. I had never worked with polyester before although the guys built campervan ends with it before moving out. I cant smell epoxy but I sure can smell polyester and I don’t like it. It is a deep blue color before being catalysed and you only use 15ml of catalyst per litre of resin. Once the catalyst is mixed in the resin turns green (at least I think it is green, I am color blind) so you know when it is mixed. It is runnier (thinner) than epoxy which in this case is a good thing. i am only wetting very light cloth. I started by wetting out a layer of cloth on the sticky tape lined roof, then I laid the filler core over the wet glass and wet that out, finishing the sandwich with another layer of surfboard cloth and wetting that out, before running the detail (consolidating) roller over it to get wrinkles and bubbles out.
Because I want to be sure the edge of the liner is stiff so that the joins are nice and clean I and because the nidacore layer will be thicker than the sides I decided to run an extra layer of filler up the edge. I will trim that to a nice straight line once it is set. I was surprised at how thirsty the filler core is. It really used a lot more poly resin than I thought it would. Fortunately I bought 20 litres ($125). I used about 2 thirds of it so about 14 litres over the 2 ends parts leaving enough to do the centre wet out. I used a brush to wet out around the edges so as not to have too many spills over the edges then I poured resin on and used a squeegee to spread the resin out. This has 3 advantages, it is much faster, it ensures that the resin is spread evenly and does not pool or too much resin and it also squeezes or pushes kinks and bubbles out of the wet out to the edges to ensure no bubbles. I then finish the job with the detail roller and every five or ten minutes I go over it again as bubbles still rise as it heats to set.
By the time I got to the end of the second side the resin was going off much faster as the midday heat in the shed was causing the resin to go off faster. I barely had time to detail roller the second side and it had already gelled off and the few remaining bubbles would not stick down. No matter, this will be upholstered so these tiny lumps should not be visible and structure is not a problem.
Tomorrow when the side parts are set I will remove them from the roof and make the centre part, then once that is made and set I will trim the sides to size and a nice straight edge ready for upholstering. I will them put them aside for a while until I am ready to internal trim. I will most likely use a professional trimmer to upholster the various trims I will make over the next year or so. Some parts will be trimmed directly onto the boat (bulkheads – walls) but all upside down (roof) sections will have panels made, especially the curved sections in the hull to deck turn and the roof sections I have just made.
Hopefully I will get the rest of the roof finished next weekend including shaping the cockpit overhang. I will also add another layer of roof to the cockpit to stiffen it and to add some thickness to make fitting the sliding sunroofs easier, I may also fit them and the ag pipe edge which will also add stiffness to the cockpit overhang. I have decided against any bog work on the floor off the boat because the roof is still so flexible so there really is not much point fairing an unstable shape until it is glued to the boat and stable.
Next month should be quite exciting. The roof should go on.