I don’t know about you, but I really hate sanding & painting and I like to save as much weight as possible when making hulls, if I can save weight to have some movable ballast for improved weight distribution, all the better.
I have yet to try making a female mould, doesn’t make much sense for all that extra work when you laying up by hand, if I had vacuum bag I would give it a try, but the extra expense of materials for mould & vac and consumables just puts me off the idea.
For male moulds I’ve tried it all plastic rubbish bags overlaying wetted-out cloth, stretch film wrap, heat shrink wrap and then started experimenting with latex on some moulds and have finally perfected the latex male moulding process that I would like to share. The latex is light brown in colour and semi-transparent (can see through it) and approx 0.50 mm thick and stretches about 50% of its original size, comfortably. You can find it at most baby shops, they use as for protective waterproof cover over cot mattresses etc.
Step 1: Cut the building board so that it is 5 mm narrower than the deck line (understanding the hull is upside down on the building board) then cut same 5mm out of the frames so there is an soft slope from the sheer-line to the base of the building board.
Step 2: Screw a 50 x 400 mm beam to the underneath of the building board so can clamp onto a mobile bench so that there is plenty of room to reach the base board, for stapling the latex along its edge.
Step 3: Drill 5 mm holes in the base board & one frame near the bow, centre and stern of the hull, this so I can lock the mould frames to the base board using plastic tie downs to prevent any movement as I stretch the latex sheet over the mould.
Step 4: Mask along the edge of the base board wrapping it over the frame channel to stop any epoxy dripping into the base of the frame, as I want to take the mould off the base board to use it as a hull cradle when fitting out the hull later. Apply another strip of masking tape under the sheer line along the mould so that it over-laps the tape on the base board. If you have cut a slot in the stern frame, pays to cover this as well to stop any epoxy getting in.
Step 5: Prepare the mould with required amount of wax & just for extra security I wipe a layer of PVA release agent using a sponge to help easily de-moulding the hull later.
Step 6: Next prepare 3 x 5mm balsa strips to staple the latex to the base board, cut it so there are two pieces for each side of the board, I’ll explain why in a little bit.
Ready to go !
Step 7: Cut your cloths as usual and then for this type of laminate I found epoxy with low viscosity works best: Resin @ 400 and hardener @ 200 (R&G Epoxy resin HT 2) for the hand lay-up. It wets out cloths nicely and allows air bubbles to be rolled out easily and is a super transparent (water clear) high gloss that has 45 minute pot life, hence plenty of time to work it. www.r-g.de (site is also available in English)
I tried various other higher viscosity epoxies, but found when the latex was stretched over the edge of hull; I could not roll-out air bubbles or excess resin (under the latex) over the sheer line pressure point.
For this lay-up I used 245 gsm twill carbon fibre as the first layer and have added dark blue U.V resistant colour paste to the epoxy which will be used with the carbon and the two outer hull 80 gsm fibre-glass layers to give the final hull colour.
For the 245 gsm, I wetted the carbon out on an old clear plastic table cover on the bench before carry it to the mould, very simple clean way of working (thanks for that tip Jim)
I use liberal amounts of epoxy on the all clothes as the wetted out cloths are sandwiched under the stretched latex to the mould, excess epoxy flows to the mask taped base board and you should not have any problems with pin holes in the finished hull. When you’re happy that the wet laminates air bubble free, apply another coat of epoxy on the top cloth so that it floods the top cloth, but not too much that it begins running.
Step 7: Using latex sheet 50cm wide x 100cm (mould is 120 cm long) lay it centred over the mould so that it hangs equally done the sides of the mould. I drew a line along the centre of the latex sheet so that I could keep an eye that didn’t move too far to one side or the other.
This is where you will need another set of hands, preferably two if available. Firstly using staple (6mm) the latex to the base board across the stern, then stretch the latex along the length of the hull until it covers the bow, pulling the latex toward the floor, equally on both sides. (don’t worry about the centre part of the mould yet)
Step 8: Now at the bow only, staple each side of the latex to the base board with staples approx 2-3 cm apart at the bow end for first 10 cm. So we now have the bow & stern stapled to the base board.
Step 9: This next step is important DO-NOT staple the centre part of the mould, you now need to smooth out the latex over the mould with your hand and then using hard sponge or rubber roller, ROLL OUT the AIR between the latex and the wet cloth. Start from the centre line running roller down the sides until you’re happy that you have all the big air pockets rolled out. You will see smaller pin head air pockets under the latex, don’t worry about them yet, we’ll take them out later.
Step 10: Now with one person each side of the mould, have them equally start pulling the centre section latex toward the floor, as you staple the balsa strip (over the latex) to the base until both sides are completely stapled to the board.
Most important, DO-NOT release TENSION of the latex until both sides are stapled down, otherwise, as the latex un-stretches, it will gather the wet cloth up the hull under the latex and you will have a hell of a time trying to rescue it (depending on number of wet layers you have)…believe me, I aborted one hull when tension was slowly released and it had moved wet cloths too far before I realised what had happened …then it was too late.
Finally after stapling has been completed you can finally roll out those small pin head air bubbles until you can’t see them anymore and you’re done.
One beautifully finished glossy hull, NO fairing, sanding, primer and more sanding and painting which gives significant weight saving estimated around 80-100 gsm. Whole exercise takes me about 20 mins.
With a normal hand lay-up, when the fibre had gotten hard enough I would trim of overhang, with latex, it is hard to see when the cloth is ready (can’t touch the cloth) once I peeled the latex off too early and the cloth moved as it was still too tacky, so now I just leave it until it fully cured then, Dremel off the overhang excess cloth.
I’ve found you can use each side of the latex once with epoxy, tried washing it warm soapy water but could not get all of the epoxy off completely, if anyone has any helpful tips I would appreciate it.
It is an easy and clean lay-up, hope my learning’s are helpful to anyone else wanting to try this method; I for one will only use this method from now on.