fiber glass question

[kbidwell]

Hello Gentlemen!

So check it out. This is a ceder strip canoe that our students here at the high school have been working on for two years now. They are doing a fantastic job! Especially considering they have never done anything like this nor has our shop teacher, all rookies! Me? I try to sneak down to the shop when I can but don't do much other than drool on it and offer a tid bit of advice when the opportunity presents.

Here are some photos of where they are at as of today...






What you are looking at represents a tremendous amount work completed, huge props to those students! She'll be a beauty on float day

Now, they are prepping to lay glass in a day or two and I have a couple concerns. I just want to make sure they are headed down the right path here.

You can see there the dark spots on the hull. They have tried to fill in some voids in the wood by using this System 3 Epoxy...



Now, at this point, they have been instructed to begin laying glass.



Concern/Question #1

On those dark spots...

I'm a little concerned that those dark spots may show up once the glass is laid?? I realize that in the glassen process the wood will be wet out, then the glass, then wet out, and during the first wet out, it should/may blend in? I'm just a bit fearful that there will be dark splotches showing through.

Fear justified or unjustified?

Should they sand out the blotches? Should they put a full coat over the whole boat, to blend in from there (so to speak) and then carry on with glass work?



Concern/Question #2

The boat is obviously going to have a few very small voids here and there given the construction. Should they take the time to make it totally, perfectly flat? Get rid of any sort of voids? The reason I ask is I am just a bit concerned that there may end up being "air bubbles", you know, that sort of situation. This is a straight up glass man question that I have no idea if this could happen. Please know any "voids" are very small. I can just get a piece of fingernail in a few of them.

Should I be concerned out this? Or, not so much.

It seems at this stage, right before the glass goes on, this hull needs to be spot on. Kinda seems to me like a one shot deal once the glass goes down.

But what do I know, just a metal banger eh.

I have just a follow up question or two but let's start here eh?

Thanks

 

[pklonowski]

Do you know what instructions they're following for the build? Do they have a book, or something more than "winging it?"

The voids will create air bubbles under the epoxy & glass, and as the epoxy cures, it'll heat up, causing the air bubbles to expand, and making a bigger air bubble that looks awful. These should be filled prior to glassing; use a mixture of epoxy and wood dust (like from a random orbit sander's dust bag) mixed to the consistency of peanut butter. Force it into the gaps with a putty knife. When it's all cured, give the hull a good sanding to level out the lumps, and that'll get the dark smudges evened out as well.

I'm not convinced that wetting out the hull before putting the glass on has any actual benefit, but others here have more experience than I... Hope they'll make suggestions...

 

[Todd Bradshaw]

It always pays to fill everything you can before glassing. In addition to bubbles you can also sometimes get areas where the cloth bridges the gap, but the resin drains through leaving something that resembles screen wire over the gap. They're a real bear to get filled after the fact.

Wood dust works, but there are two things to know: (1) the cured fill is much harder than the wood around it, so sand it smooth with a sanding block to prevent dishing the wood and (2) wood dust fills are essentially all end-grain, and like end grain on a board, when you saturate it, it will get much darker that the rest of the board would (or your strips will). So you want to use lighter colored dust to make the fills and test it against saturated strips (like the dark spots) to check for final color of the strips and mix. If need be, you can also mix in some ground up colored or white playground chalk to lighten the color of the mixture.

There is really no reason that the spots should show once the glassing is done as long as it's the same resin.