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Just about to complete my build of Chesepeake 17LT. Below is what I didn't learn from all my research and reading the manual and found out the hardway. Nothing against the documentation which is excellent, just flagging for other like myself who think they know better.....
1) Never sand glass resin with wet sandpaper. As soon as you get to the fibreglass cloth the water gets in and stains the matting so you get an ugly stain. Always dry sand.
2) Keep the fibreglass cloth pristine clean. I had a few drops of sweat and other stuff on the cloth and turned it ugly opague under resin and varnish.
3) Found it totally impossible to get the right level of radius at end of bow and stern for the deck when the plywood is less than 2 feet wide as no leverage. Should have kept it wide to enable the straps to bend to correct shape, rather than trim to width of kayak before attaching.
4) if like me you are doing multiple layers of fibreglass (I did an extra 2 inch width strip of cloth down the keel), either do all layers at the same time, or do the narrow extra strips on top rather than underneath. The ridge from the edge is impossible to fill with another layer of cloth.
5) Still in the dark whether its better to fill the weave with resin vs fill with varnish vs leave with woven effect and save weight. I left the deck and inside cockpit with weave showing, which worked well except issue 1 above.
6) The pros say the resin is the biggest cause of additional weight. for me it was the paint/varnish...3 tins later...
7) Not sure what its like in rest of world, but in Singapore there is huge variety of density, strength, and finish for marine plywood. I learnt a lot when I did my strip joints and saw the real thickness and quality of wood. Pays to shop around first.
The bright side is that despite the above the kayak looks amazing and goes in the water this weekend.
2 replies:
RE: What they didnt tell you
Not sure if i qualify as a 'pro'....but have built quite a few of these at a very high quality of build and finish..
fwiw....i think you are conflating dry weave or other phenomemnon that occur when the glass is not properly/fully wetted out...vs what you can expect with properly wetted out e-glass.
so the first issue is, is the weave fully wetted out. if it is fully wetted out, and you are using the right grade of e-glass, it should become clear....even if you can still feel the weave.
as far as my experience, once it is fully wetted out, it can be dry sanded, wet sanded, or sanded through with no obvious optical difference. if it is sanded through, it will be weaker and you should patch it, but it should not leave a mark. that said, i avoid wet sanding prior to applying a finish becuase it is relatively easy to sand through to bare wood (expecially on chines) and you don't want to get water underneath the epoxy/cloth. but fully wetted out epoxy/cloth is impervious to water once it is cured.
that said, there are lots of reasons glass doesn't get fully wetted out....and when it doesn't, it becomes visibly obvious. one good example, is outgassing and little bubbles that form in the resin and get trapped in the glass....and when you sand down into them, the bubbles fill with dust and when you overcoat them with epoxy...the dust is trapped in the little bubble and it makes little white speckles. or when you starve the glass becuase you didn't apply enough epoxy and the glass becomes whitish or cloudy. and when you sand into that, it certainly doesn't improve the situation...and makes it look worse.
the other experience that comes to mind is when you are sanding a not fully filled weave, epoxy dust can get into the divots.....and if not cleaned out before overcoating, can leave white dots similar to what i described above with bubbles. one of the techniques i use to minimize any problems of dust in bubbles or divots, is a very liberal swipe of denatured alcohol over any sanding run that appears to have left these little dust bubbles or divots... to litterally wash away the dust and allow the next layer of epoxy to come in very clear. if it is clear under a wipe of denatured alcohol, it should come in clear with the new layer of exposy. sometimes, on occassion, i have had to use a little toothbrush to clean out dust from bubbles or divots that did not get taken care of with the generous swipe of an alcohol filled wipe.
anyway...i hope this helps.
h
RE: What they didnt tell you
» Submitted by Birch2 - Mon, 1/9/17 » 7:43 PM
Point #1 really interests me. My take on it is -- never sand through the epoxy resin to the fiberglass cloth below. STOP the instant you see that happening. I sanded through (dry-sanding) in a couple of places. As soon as you do that, You will get fiberglass dust down into the weave and there will always be a white weave pattern visible in that area. As least that is what I think happens. I'd like to hear from one of the real pros about what to do if you sand down to the weave.