Need help and advice - fiberglassing new wood boat

3.5 ounce cloth will be as effective as 6 ounce for about half the weight (typical of all the light weight cloths). It'll take about as much epoxy to wet out as the weight of the fabric. So, 23 yards (205 sq. ft.) is 80 ounces (a bit over a half a gallon) of goo if 3.5 ounce fabric or 138 ounces (a bit over a gallon) if 6 ounce cloth. To fill the weave, you'll need about half as much more, less if you thicken it first.

 

Par,

How can 3.5oz cloth be as effective as 6 oz? Do you mean strength or abrasion?

If you said 6oz was just for surfacing and I need something heavier, how can you turn right around and say the opposite?

I assure you where I work twice the material gives you twice the strength.

I also tried 4oz cloth instead of 6oz and it seemed to be less beneficial for abrasion.

Just my experience. You do have an interesting rule of thumb for epoxy usage. I'm going to try to see how it works on the next boat. I assume your 138 figure above would easily be supplied by 1 gallon of resin, since you have to add in the hardner.

For West system 1 gallon of resin requires .3 gal of hardner so 128 x 1.3 = ~166oz mixed epoxy. The West System area calculator says 1 lamination + 3 fill coats for 23 sq ft = 0.3 gallon. It would be interesting to see who is right. I assume I used the formula correctly.

 

You aren't getting any strength from a single layer finishing cloth (okay a measurable amount, but nothing to be concerned about) and the abrasion resistance is minimal with these cloths anyway, so why carry all the weight on a boat, where ounces matter. In short, the abrasion resistance of 3.5 is about the same as 6 ounce, so save the weight and use 3.5. This said you do have more film thickness with 6 ounce, compared to 3.5, but most don't let their boats saw away on rocks until the wood splinters fly, before considering repair. In other words 6 ounce is more durable if you grind up against the rocks a lot, but this said, neither 3.5 or 6 ounce offer very much protection, just casual bumps and abrasion, so go with the light stuff and save some weight.

West systems formula is rough, as is mine, but if you use West System's technique, you'll need a lot more epoxy (which is just a good business decision on their part don't you think).

 

Last try.
Yet again we need to know the boat and usage.
You continue to discuss apples and oranges - "neither 3.5 or 6 ounce offer very much protection, just casual bumps and abrasion" and yet you talk about "let their boats saw away on rocks until the wood splinters fly".
Your thumbrule predicts ~1gallon for 6oz cloth vs 0.3gallon for the West formula -"but if you use West System's technique, you'll need a lot more epoxy". Unless I did the formula wrong the West System technique predicts 1/3 the amount of yours.

Dave T talks about "if in doubt make it stout" so I can't see saving ounces by going from 6 oz to 3.5 oz. Depending upon usage he might actually want to go heavier, especially after using the boat and seeing how much damage he gets. In either case he can always sand off the paint and apply a second layer.

Dave, I sure would like to see your boat.

Marc

 

The West System technique uses unthickened epoxy to fill the weave Marc, which will use twice to three times as much epoxy as their formula suggests, which is just a wetout formula. I agree without more information on this particular boat, most of this is just speculation, but general rules can be applied, such as assuming a good hand layup with a 50/50 resin ratio, which will require as much epoxy as it does weight of fabric. Now, most back yard builders will be hard pressed to get a 50/50 layup, but it's a place to start and keeps the math easy.

 

Unthickened epoxy would be for something you want to be able to see the wood look.
Thickened certainly would save money if you are going to paint.

I am going to try your formula next boat.

I am sure I don't get 50/50.

 

An average back yard hand laminate will be 35% to 45%, with lighter weight fabrics. Heavier fabrics tend to get "ironed" down better, so a good hand laminate might be on the high side of this range. With good techniques, you can increase this to over 50%, but you'll usually be employing more pressures, peel ply, Mylar sheets, etc. Bagging and infusion can get into the optimum resin/fiber range of 60% to 70%. Once over 70%, you start running the risk of resin starvation.

 

Thanks for the info

I checked out the sites mentioned and have decided to go this way 6oz. cloth with two layers on outside surfaces total sq. footage 323 sq.ft. for cloth. I will need about 4 gal resin according to calculations from west system site. Should be less than this because the second layer of cloth should only take two coats of resin because the top coat on the first layer would be base coat for second. Here is how it adds up. 4.5 gallons no blush basic epoxy resin from epoxyUSA $89.00 /1.5 gal. with shipping $319.19. 25 yds. 6 oz. cloth from fiberglasssite They seem to be the cheapest and there cloth is 56" wide which means it will cover 1.5 yds. $175.00 with shipping. Total $494.19. Does epoxy have the terrible fumes and odor like polyester? If not I could sheath it in the shop this winter as soon as I get the trailer built. Right now my boat is in an unheated shed wrapped up in tarps. I would like to make maiden voyage April 15 the 100th aniversery of the Titanic sinking.

 

Dave,

Most people dont' think epoxy is very bad. Certainly not like Polyester. But you will want to be able to have the area heated if you do this in the winter. The epoxy slows down a great deal in the cold. Keeping the cans of epoxy and hardner warm also helps make an easily applied laminate. I have made a "oven" out of cardboard boxes and used a small bathroom heater to bring the temperature to 100 degree f. I had to bring a hose from the other end so the air inside the box gets recirculated. You do need to watch closely to see that the heater doesn't get too hot.

If you were to do this soon you could use "slow" hardner, here in Texas my last lamination on a kayak took about 3 hours to harden (85 degrees today), if you are going to do this in cold (60 - 70) you ought to use the "fast" hardner. I think you should not be curing in 60 degrees, the shop or something needs to be heated.

Good luck, post the pictures when you get done.

 

Do both 6 ounce layers at the same time and save yourself some trouble. fiberglasssite epoxy is $95.95 for a 1.3 gallon kit (resin and hardener), which works out to be $73 a gallon and a lot more then Epoxy Products or Bateau.com's Marinepoxy. You should check your prices again. From memory, Marinepoxy costs less then $65 a gallon, including hardener if you buy small quantities. It's less then $60 if you buy 3 or more gallons.

 

Par

When you go to bateau.com and click on their epoxy it takes you to Boat builder central their prices for resin are $67.50 for 1 gallon without hardener, $96.75 for 1.5 kit, 3 gallon kit $163.50, $243.25 for 4.5 gallon kit. epoxyUSA is where you end up from the other site you mentioned. Their price is $89.00 for 1.5 gallon kit or $267.00 for 4.5 gallons. There's probably no difference in these two resins but epoxyUSA does a better job of advertising saying theirs is better because it's solvent free and no blush which is probably bull but people like me will buy it because we don't know any better. I was not planning to buy resin from fiberglasssite only the cloth. What is a good reasonably priced marine paint for both top and bottom. I checked at our local Menards and they have bottom paint at $36 a quart and top paint at $12 quart. I assume paint is the way to go rather than adding color to the top coat of resin.

Thanks,
Dave T

 

How about use epoxy resin only (no cloth) everywhere but the bottom. Cloth doesn't bring any strength to the party anyway, and a few coats of epoxy will provide all the vapor barrier you'll ever need. Save you a bunch of weight, cost and time, and you won't really be giving anything up at all.

Steve

 

A light layer of cloth does dramatically improve abrasion resistance compared to just epoxy coated surfaces.

 

Since then I have dealt with the manufacture and use of these materials one I understand. That you pay you get. The question is do the job you want?

 

Hence my suggestion:

How about use epoxy resin only (no cloth) everywhere but the bottom.

Abrasion resistance is typically not that big a deal on topsides for instance. I've seen several small boats made out of 1/4" plywood with just epoxy that are still going strong a decade later. Worn paint on these boats tell where the abrasion resistance needs to be, very little to none on the topsides.

Steve