thanks and no thanks Circlip
the thanks really goes to the Companies who tried to educate me in the use of fibre glass resin and what I have learned I do try to pass on. Although, when I have done a bit of research this afternoon some of the techniques and materials have drastically changed, since when I first was involved with commercial products.
Just a few more pointers, to help people which I notice hasnt changed, when working with fibre glass resin there are several hard and fast rules which must be adhered to whilst working with fibre glass or even epoxies and they are well documented in other topics on this forum. One of the main pitfalls, which I have seen are people who are new to the fibre glass scene, as you have already stated, tend to add too much hardener. The other one is, that people think the more laminations you add to a hull, the stronger it becomes. I have seen models of some 4-6 feet in length, with hull thicknesses varying from 3/8 inch thick up to 1/2 inch and around the stern section, and, the rudder supports being laminated up to near enough an inch thick. When laminating to this thickness around sub structures this will only bring on problems later on in the life of the hull. As has already been stated, fibre glass moves and shrinks, causing problems.
Its trying to educate people that a hull of 5 feet in length need not be 3/8 inch thick to have strength, merely only 1/4 inch or even less. But, to add strength to the hull by adding longitudinal stiffening down the centre of the keel by means of say, laminating in 1/2 inch square softwood with two layers of matting over the top, and the same around the sides of the vessel - maybe 3/4 inch down from the deck line, when these had been laminated in, one would be surprised how rigid and light the hull would be.
The other thing I have seen in some hulls is what they call 'resin rich' which is where too much resin has been mixed and what they have done is just worked it into the hull.
A good rule of thumb, as we were taught, the ratio should be 2.5 to 1 of matting, a good experienced laminator should be able to work in 2lbs (two pounds) in weight of resin for every pound weight of matting. An average laminator between 2 and 2.5 lbs weight of resin to every pound of matting. If you are just a beginner 3 to every pound of matting, but then you are starting to over-saturate the matting. With a good roller, and a good rolling technique one should soon be able to work at the 2.5's.
The other thing to mention is, if at all possible, and you are new at the game, try and work with clear resin with no pigments in. The reason for this - airpockets and airbubbles - are easily detected and can be worked out before the laminate goes off (bit like wallpapering - yikes :) ).
The last thing I would mention for beginners is to try not to lay too many layers of matting in one go, try and plan so you work alternatively i.e. from corner to corner on large hulls, therefore avoiding heat generation.
Hope this is of some help.
aye
John E
Bluebird