Glassing fir to prevent checking

What’s the consensus here on weight of glass to prevent fir from checking? I’ve read anything from 2oz to 6oz. 2oz seems pretty light, but is 6oz really necessary? Hate to put 6 if 2 will do it, but I don’t want to find out 2 was really too light one day down the road. Just go with 6oz?

And just to confirm, this is plain woven cloth, not twill or something else, right?

Jbo

 

Will you be using epoxy or polyester resin?
I think that it will depend a lot on the thickness of the fir that you want to coat in fibreglass (I presume that this is what you want to do?).

 

Only epoxy for me.

Why would the ply thickness matter? Isn’t checking just on the surface? To answer the question, it will be 1/2” and 3/4” AB marine fir.

Thanks.

Jbo

 

My apologies, I thought you were going to glass solid timber planks, rather than plywood, hence the question.

Are you laying a fir plywood deck, or will this glass be on the hull?

 

At least a deck for the time being, but I own the wood and I’m getting the itch, so sooner or later some will likely become a hull.

Though I guess on the hull is moot on the outside at least, since it will probably sport some biax cloth anyway.

Jbo

 

If you’re using it as a deck, I’d tend towards heavier glass, for protection.
2 oz will be eggshell thin, very susceptible to damage, 6 oz proportionately better, but IMO, still not enough protection for a deck.
Proper priming and painting should be enough to just prevent checking, if the lumber is dry.
Of course, this all depends on variables not stated here.
Are we talking about a flyweight racing boat, or a commercial trawler?

“I’m getting the itch”, LOL, that will come soon after the resin hardens!

 

Definitely not building a flyweight boat with fir. Just replacing a deck on a bass boat right now, but will be building a small “trawler” of sorts soon enough.

Yes, ‘the itch’ manifests itself in different ways at different times.

Jbo

 

Title of thread, no mention of plywood.

From OP

Second post first mention of ply...

2 oz would suffice to stop checking.