How many layers fiberglass on new deck

[skenn_ie]

I suggest a foam sandwich. You will get stiffness with much less glass/work. Depending on how much compound curve the deck needs, you could glue together the foam, remove it from the boat, glass one side, then put back on with glass on the underside, then glass the top side in situ.
A benchmark for mat/cloth that I read years ago was mat : resin 1 : 2 or 2.5 by weight. Cloth 1 : 1. Foam will take a bit more resin to fill the pores. DOn't forget that Epoxy doesn't work well with mat. The bonding agent in the CSM needs to dissolve, and that doesn't happen with epoxy. I also recommend poly-vinyl foam or high-density PU. The lighter stuff peels too easily. I made that mistake. Microballoons are good too, mix a slurry and use that to fill the pores (homebuilt aircraft practices).

[DeaneW]

Originally Posted by theglo

I'm doing my shopping for our haulout next month. We are replacing a few large areas of the deck that are shot and causing sponginess and water leaks in the cabin. Boat is 45' Dufour.

I'm planning on using this lay up over the new core:

1.5oz mat
24oz woven roven
then
1.5oz mat
24 oz woven roven
and then
10 oz cloth to finish

Any ideas on what type of thickness that may deliver?

Is that sufficient or should I add another layer?

Any other suggestions? Planning to order this soon so its on hand before we get in the yard. THANKS!

I would suggest that you use 5 layers of 800gsm double bias cloth and epoxy resin - this will give you far more strength and less work than what you have proposed. Use peel ply to give yourself a smooth finish.
Cheers
DeaneW

[Hamish_ct]

Unless the part of the deck is taking on any load or a winch, then carving out all the wet balsa core and replacing with Fiberglass is complete overkill and very heavy. replace with Balsa core or marine plywood, then add a layer of Fiberglass so the deck will adhere nicely to the work done.

It's not worth the cost or time to re-layer with glass. If the spot is holds a winch, or something else that is load bearing, then and only then replace with Fiberglass matt.

[wingssail]

Originally Posted by Hamish_ct

Unless the part of the deck is taking on any load or a winch, then carving out all the wet balsa core and replacing with Fiberglass is complete overkill and very heavy. replace with Balsa core or marine plywood, then add a layer of Fiberglass so the deck will adhere nicely to the work done.

It's not worth the cost or time to re-layer with glass. If the spot is holds a winch, or something else that is load bearing, then and only then replace with Fiberglass matt.

When balsa or marine ply is not available I have used generic soft wood such as pine. In most countries there is some kind of similar soft wood available. Saturated with resin or epoxy it resists water and it usually has good adhesion and compression properties and it is lighter and easier to work with than plywood.

Photo: Replacing the core around a hatch opening with pieces of soft wood, (the skin has been removed intact) 20 pieces in so far. Next fill all gaps with slurry of resin or epoxy and filler. After that, replace the deck skin, either the used one or a new lamination.

[s/v Jedi]

So I looked this quote from Dave Gerr up to get it completely:

“ A typical stitch-mat is Hexcel Knytex DBM1708. This is a +45, −45 bi-axial (the “DB”), built from two layers of 8.5-oz./sq. yd. uni-di (totalling 17 oz./sq. yd.—the “17”), with a single layer of ¾-oz./sq. ft. (0.75-oz.) mat stitched to it. (The “08” is for the 0.75-oz. mat, rounded off.)”

So he is right with his units and my suggestion of 08 being 075 rounded off was not so weird either.

The whole section clearly indicates that OP should use 1708 for deck repair. Skipping the mat can be done for new construction in optimal vacuum bagging setup, which a deck repair is not... not even when using vacuum bagging.