What is the appropriate weight/schedule...?

Hello knowledgeable folks!

I am in the process of removing the teak decks on an older, kit finished Westsail 32. It is a flush deck design, with a double layer of 1/2" plywood and laminated beam structure and topped off with a fiberglass skin. The result of ripping up the teak has been the unintentional removal of the fiberglass skin that covers the plywood deck structure in many areas. For consistency's sake, I proceeded to strip the deck of the remaining fiberglass skin, leaving bare plywood.

I am now trying to research and plan for laying down a new fiberglass skin on top of the deck, to be painted with (to be determined later). I am considering using a marine grade polyester resin and one (or several?) layers of 1 1/2 oz mat to cover the decks.

I understand the limitations of using polyester resin, but when looking at the cost of re glassing most of the/entire deck of a 32 ft boat, it is more in line with my budget than epoxy. Or is it? Although I would prefer to use polyester resin, perhaps an epoxy layup with a thin cloth could compete.

My question: What schedule and combination of poly/epoxy and mat/cloth would you recommend for the deck skin, with an emphasis on relative economy?

If I understand correctly, the fiberglass skin is not as much a structural component of the deck as an abrasive/waterproof barrier, so what would the minimal amount of adequate material be, in your opinion?

I appreciate your thoughts.

 

If your plywood is thick enough to hold the weight of passengers say 40 lbs. dead weight per square foot, then a single layer of glass (no mat) of 7 oz. will waterproof it. Any further layers would be for hard ware and tear. Put some clean sand in your final coat of paint to help with slips.

 

A local friend in the industry recommended 10 oz cloth, which seems to correlate with your advice of a minimum of 7oz + extra for wear and tear.

I don't understand why successive layers of matt aren't as acceptable as an equal amount of cloth, though. Is cloth more cost effective by weight? or just inherently superior?

 

Cloth weight is per square yard while mat weight is per square foot. 1.5 oz mat weighs 13.5 oz per square yard and 10oz cloth weighs 10oz per square yard. I have no idea why it's done that way.

 

This chart might help. It's in the third post, click on it a few times to make it readable...
http://www.boatdesign.net/forums/fiberglass-composite-boat-building/fiberglass-thickness-8686.html

 

Today I learned! Thanks to you both for the insight. The chart is showing up too small to read, but perhaps you could provide a hyperlink?

Cloth is inherently stronger stuff, but if the strength of the deck is in the plywood and beams anyway, maybe a layer of mat or two would be fine.

 

Your epoxy resin costs will not be that excessive on that boat. You'll need about 3 gallons to wetout and fill the weave. This will run about $160, unless you use a major name brand, which will cost 2 - 3 times as much.

Multiple layers of a lighter cloth, say 4 or 6 ounce is preferable to a single heavier sheathing. Two 4 or 6 ounce skins will do.

Talk to Paul over at Epoxyproducts.com or Joel at Bateau.com for good pricing on epoxies that preform as well, if not better than the mane brands at half the cost. Tell them PAR sent you.

 

Try clicking on it. 1 click for medium size, another click for huge. Try that.

 

Two layers of plywood laminated over beams is massive, any sheathing is just to provide a surface which is waterproof and a good base for a paint system and is also more impact resistant to protect the plywood from dropped winch handles etc, for this you dont need multiple layers of anything, one layer of cloth enough, i would use dynel, xynole or 6 to 8 oz glass, glass is not as good for impact from dropped sharp objects,it is after all glass, whichever you choose please use epoxy. As Par pointed out there are lots of less expensive options to the big name brands, aeromarine is another good one. Dont use polyester on wood, dont use mat.

Steve.

 

Dont use Polyester resin. Even if someone gave it to you for free.

This link is a test for impact resistance of various fabric deck covering. As you can see "Sglass" cloth is desirable. Be aware that glass cloth comes in different weaves as well as weights. dense weave will be more resistant

http://www.oneoceankayaks.com/Abrasion.htm

Ive had good luck covering small craft decks with 6 oz cloth. 9oz sounds good for a big heavy boat.

Ive never covered a deck that was big enough to consider multiple layers of cloth.
The advantages to multi layers is that you can butt joint the fabric , insteaad of overlaping the cloth edges and fairing them in.

I have no experience with dynel zynole . These clothes are widely used by professional boatbuilders for deck coverings. Ask your supplier for glass cloth weigh equivalents.

 

Use epoxy, you'll thank yourself.

I used 6oz epoxy cloth. The process was as follows.

1. Seal coat using system 3 clear coat resin. Sand lightly
2. Follow up coat of System 3 general purpose resin. Sand lightly.
3. Lay 6 oz cloth on cured resin surface.
4. Apply resin to cloth using a squeegee.
5. Follow up first coat of resin with one or two additional coats to fill weave.
6. Paint. I used Interlux 404 Epoxy Prime Coat (2 coats) and Interlux Perfection (2 coats). You can apply non-skid on the final coat.

I'll attach a couple of photos I took during the build. The foredeck is 1 1/8 inches thick Douglas Fir (1/2" + 5/8" laminated). I can verify that the cloth adds abrasion resistance, but not much impact resistance. Drop a good size wrench, say 3/4" and you'll leave a ding. Just be mindful and you'll be fine. I can jump off the flybridge onto the foredeck and it feels solid as concrete.

Good luck and have fun,

MIA