Pleased to report that with helpful advice from your tech team and some forum members I have now successfully made up 6 flat c/f panels in 195 gsm varying from rectangular 400 x 400 mm to triangular 2200 x 450mm by resin infusion. All have eventually come out without voids (yipee), there was some scrap. They only worked well once I heated the layup table to 22c, and heated the resin as it flowed with a hot air gun. I did use a lot more resin than in your tables, but the surplus came off in the peel ply. My panels are 0.35mm thick.

Now can you you help me with sticking these on my grp boat?  I have coarse sanded all the grp, 80 grit. I cannot control the temperature which is ambient in a big steel shed, currently 3c and 65% humididty. I therefore cannot use epoxy the glue them down, because any minor  uneven heating / cooling causes ripples, I have tried. The surface is compound curve, just, but I have formed the panels dry, by heating them till flexible and taping them down to cool. (It works!) I favour using pu 18 adhesive as it is flexible and waterproof, but how on earth do I get an even thicknes of such a thick sticky adhesive over such a big area??? and how do I keep the panels even on top of the adhesive?? Any advice and or clues would be greatly appreciated.

Good idea bruce!!

PU18 can be spread using a tool like an adhesive comb.  I have spread it for when doing my bonnet for bonding two parts together.  I just used a credit card sized piece of plastic.

You can thin PU18 down with acetone to a thinner consistancy. I have done this before to paint the black borders around a car window.

however try this on a test piece first as im not sure on the effect of its bonding ability the acetone will have. 

Hi ezsailor,

Sorry for the late replay, I've been away for a few days and the rest of the guys in the office have been flat-out. I'm glad you got the sheets spot-on in the end so it's on to the next tricky thing!

Bonding such thin sheets without any rippling is always going to be a bit of a challenge because as you now a slight variation in the thickness of the adhesive will show through. For this reason it strikes me that you need a thin resin rather than a thick adhesive. The problem, as you've already mentioned, is your ambient temperature. Because the panels are large and I suspect that, as Bruce has pointed out, vacuum bonding would be the preferable way of holding them in place you're going to need a decent working time which rules out using a very reactive resin to overcome the cold working environment. Is there no way you can use some localised heating (like halogen lamps) shone on the surface after bonding to get some heat into the panels (and the adhesive underneath). In my experience, even though these halogen lamps might have little impact on the ambient temperature in such a large cold room they can be very effective at heating the surface of the part/mould and so might be a solution to an otherwise difficult problem.

You say you've opted for PU18 because it's flexible and waterproof (which indeed it is) but water would be no problem for any of our epoxy resins or adhesives, or a methacrylate or polyurethane. As for the flexibility, how much 'flex' do you need or anticipate?

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Iv'e been away for a couple of days as well. Thanks for the reply. Flexing is fairly small in terms of twist, probably less than 2mm in 500. But downwards deflection could be as much as 10mm in the 300 mm between the deck ribs, if you accidentally stand on it (easily done)  I see what you are saying about uneven resin thickness though. I tried epoxy resin with and without filler powder, seemed not to make a difference. Got two on perfect, and four were awful next morning. I was lucky to go very early and managed to rip them off before they were properly cured.

I thought of PU18 because I am familiar with sicoflex, and know you can spread that with an adhesive comb to a fairly even coat, while leaving some thickness to take up very small imperfections in the substrate. Supreme being says it can be combed, and if I smooth it down with a 500mm  long board with layers of soft cloth on the edge (which must help to even it out) and then vac it down do you think I would get better control over it? I could try the smallest piece first. I have to get this right now, the other guys in my club already think I am some sort of magician.

PS Actually Matt I think what's causing the ripples/big air bubbles is the lack of initial grab that epoxy suffers from. Where they appeared could be clearly seen on the underside  when the sheet was removed, lots of tiny pointed peaks where the bubbles were, and clear combed flat lines where it gripped. Does PU18 have better initial grab?  Using vac to hold down will help to overcome this premature release? Thanks.