Correct order to fair and glass?

[Noklin]

What is the correct order in which to fair and glass the hull?

I can see advantages both ways.

Since the fairing compound is soft for easy sanding, it would seem that glassing over the faired hull would provide better protection to the fairing compound and hull.

But since any joint in the glass would still have to be faired in, is it better to glass first and then fair the hull once.

[Charlie Jones]

since the fairing compund IS SOFT for easy sanding, I would not trust glassing over it. I'd worry about the bond to the actual wood, which is the important part of glassing.

I'd most certainly hold off any fairing with softer compounds until after the glassing.

This would NOT include however, fairing obvious bad spots around joints, etc, witha hard filler such as wood flour or silica.

One thing I'll mention here- I almost NEVER touch the plywood surface with ANY sand paper until after the first coat of epoxy is on, again except for obvious spots from joints, etc. Then I VERY lightly sand, or even better, scrape the hull, to get rid of nibs, and things that would snag the glass. I emphasis LIGHTLY.

Once the glass is on, I fill coat with however many coats I think it needs, working "hot". ONLY after the final fill coat is on and the epoxy has cured will I wash it down and then sand well. Then roll on a final coat of epoxy and resand.

Yeah- I KNOW some of the epoxys are free of blush ( supposedly) but having been bit a few times, I always wash , just in case. Water wash down only takes a few minutes and I have much more peace of mind.

Between the final fill coats and that final coat of epoxy is when I do the bulk of my fairing by the way. If needed, of course, I'll sand and recoat again.

If you are careful with ply, it doesn't take a whole lot normally- the panels lend them selves to fairness.

[Designer]

This is one of those occasions that I do things differently to Charlie. I understand his logic about not glassing over low density filler but I believe that as long as the peel strength of the filler is equal to or greater than the wood then it should be fine.

I do fair the tape at the seams with low density filler and fair the hull before glassing. I like to start glassing with a fair hull so that if I squeegee the glass down evenly I will have very little fairing to do after I fill the weave. This means that I will have very little fairing to do on top of the glass and risk weakening the glass while sanding the fairing.

[Hirilonde]

I don't think the order used is important if the right materials are used in the amounts necessary to achieve the results required and IF: ALL BONDS ARE SOLID.

since the fairing compund IS SOFT for easy sanding, I would not trust glassing over it. I'd worry about the bond to the actual wood, which is the important part of glassing.

Charlie, are you concerned about the glass layer adhering to the filler? or the filler to the wood?

Whenever I want to used a soft filler for sanding purposes, which implies a rather dry one, I worry about its bond to the wood. To deal with this I first paint out the wood with pure resin then apply the filler immediately to the wetted out surface. This gives me the saturated/penetrated bond to the wood and the soft, dry and easy to sand surface. This surface can then be sanded out to allow for a good mechanical bond to whatever layer comes next.