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Old 23-06-2016, 06:28   #1
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Fiberglass cloth weight

Hi, I'm finishing a Cape George 38 and it's time to fiberglass the deck and cabin. The deck is one layer of 1/2" Sapele and a top layer of 1/2" Doug fir on top of laminated beams 12" oc. The cabin top is two layers of 3/8" Okume over laminated beams 10.5" oc. The cabin sides are 5 layers of 1/4" Doug fir ply. All interior ply surfaces have been coated with epoxy.
Typically the yard uses mat, roving, mat and polyester. I plane to use epoxy and was thinking two layers of 10 oz. cloth. Does that sound appropriate?
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Old 23-06-2016, 07:03   #2
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Re: Fiberglass cloth weight

Seems odd that the "yard" would use that combination to sheath decks with. typically you would use 2-3 layers of 8oz ( or 10oz) fiberglass cloth to sheath decks.
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Old 23-06-2016, 08:08   #3
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Re: Fiberglass cloth weight

pcmm, Perhaps I should not have used the word "typically" to describe the way the manufacturer glasses their decks. That schedule is what was recommended. We never talked about cloth weights as I decided to go epoxy.
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Old 23-06-2016, 08:46   #4
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Re: Fiberglass cloth weight

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Originally Posted by bhenry View Post
Hi, I'm finishing a Cape George 38 and it's time to fiberglass the deck and cabin. The deck is one layer of 1/2" Sapele and a top layer of 1/2" Doug fir on top of laminated beams 12" oc. The cabin top is two layers of 3/8" Okume over laminated beams 10.5" oc. The cabin sides are 5 layers of 1/4" Doug fir ply. All interior ply surfaces have been coated with epoxy.
Typically the yard uses mat, roving, mat and polyester. I plane to use epoxy and was thinking two layers of 10 oz. cloth. Does that sound appropriate?


Two layers of 10 oz boat cloth is the standard for that. I'd consider going to three though. I'd recommend using Silvertip for laminating resin. Also, if you catch the bond window and trowel on your first pass of fairing compound while you can still leave a fingerprint in your laminating resin, it will save you a lot of work and prevent issues with bonding due to blush. Then you can go straight into fairing. Either that or peel ply it. Good luck!
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Old 23-06-2016, 21:24   #5
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Re: Fiberglass cloth weight

minaret, I was planing on using silvertip, and was under the impression it did not blush? I received an email from another member which , for some reason did not post in this thread. They talked about 1708, which sounded interesting. Is three layers of ten oz. Prefered?
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Old 24-06-2016, 00:35   #6
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Re: Fiberglass cloth weight

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minaret, I was planing on using silvertip, and was under the impression it did not blush? I received an email from another member which , for some reason did not post in this thread. They talked about 1708, which sounded interesting. Is three layers of ten oz. Prefered?
Many resin systems claim to be blush free. My advice there is you can't be too careful. 10 oz. definitely preferable to 1708 or 1700. This is because you will have a very difficult time wrapping 1708 around numerous radii on your project and are much more likely to end up with voids that way. It's simply too thick and stiff a fabric. However, 2 layers of 10 oz does not really protect well against impact like a dropped winch handle. Three does much better. An odd number of layers also allows you to make nicer tapers at joints while glassing. Better result all around IMHO.
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Old 24-06-2016, 02:42   #7
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Re: Fiberglass cloth weight

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Originally Posted by minaret View Post
Many resin systems claim to be blush free. My advice there is you can't be too careful. 10 oz. definitely preferable to 1708 or 1700. This is because you will have a very difficult time wrapping 1708 around numerous radii on your project and are much more likely to end up with voids that way. It's simply too thick and stiff a fabric. However, 2 layers of 10 oz does not really protect well against impact like a dropped winch handle. Three does much better. An odd number of layers also allows you to make nicer tapers at joints while glassing. Better result all around IMHO.
Great tips!
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Old 24-06-2016, 06:52   #8
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Re: Fiberglass cloth weight

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Originally Posted by minaret View Post
Many resin systems claim to be blush free. My advice there is you can't be too careful. 10 oz. definitely preferable to 1708 or 1700. This is because you will have a very difficult time wrapping 1708 around numerous radii on your project and are much more likely to end up with voids that way. It's simply too thick and stiff a fabric. However, 2 layers of 10 oz does not really protect well against impact like a dropped winch handle. Three does much better. An odd number of layers also allows you to make nicer tapers at joints while glassing. Better result all around IMHO.
Good to know about the blush. Is there a particular weave you recommend in the 10 oz?
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Old 24-06-2016, 07:27   #9
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Re: Fiberglass cloth weight

10 oz boat cloth is easy to lay... but tough over wood if your sanding guys, are really grinding guys. If they burn through in the inside corners, the boat doesn't have enough epoxy thickness under the paint to keep the wood from taking on water if it has anywhere at all that can gather it.

That is what causes plywood sheathing to pop fiberglass taped joints like a zipper. It gets wet, swells, and then runs down the joint.

That rots out your deck carlins, and directly you've got a whole host of problems.

To combat that, and the guys grinding... I grind tapers down into the inside corner radius at the cabin side to deck joints and tab it in with 4 inch wide strips of 1708. 2 inches into the cabin, 2 inches into the deck. I like to see half a stir stick disappear in the depth of the taper. Come back and grind it so it tapers out into full thickness at the inside radius... That keeps the corner fillets low to the rest of the deck for 90% of your fairing work.

It also means that a guy with 80 grit on an 8 inch pad sander has to have a real bad hang over to rub through the glass in the inside corner fillets and see wood.

It is very easy to pull a a 1 inch wide stripe that is a shade low before pulling a decorative fillet over the whole length. The larger the radius the easier it is to sand and make the boat look like a million bucks. I like Awlgrips fairing putty for those fillets just because it sands the same no matter what batch... Something in the neighborhood of a 1 1/2 to 2 inch pvc pip fillet. Sand out with a piece of foam board wrapped in 120 grit then rub with red scotch brite... Prime it.

The smaller the fillet the easier it is to see a wave in the line and the more perfect the deck to cabin joint has to be to look good. Batten fair and Long board sanded, before the fiberglass goes on... Which I like to see done anyway. Wood is cheap to fair, easy to sand and plywood isn't flat... Particularly if its been screw laminated on.

If you trench out each of the seams in the plywood over the deck an inch to each side with a router... then lay in 1708 with the goal to keep it a shade low of the surrounding area... and you won't have issues with cracking at the deck seams either, even if you get water penetration at a deck fitting near by.

Cheers,

Zach
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Old 24-06-2016, 07:36   #10
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Re: Fiberglass cloth weight

Forgot to say... pink builders string works very well for a batten at the inside radius of the cabin joint.

It is tough to see where a 3/4 x 1 1/4 fir batten can't touch way down low above the fillet where you have any rolling bevel along the length.

If you have a high spot down low it tends to grow into a mud pie pancake during fairing stage. What amounts to a high frame in the build turns into a job...

If the boat hasn't been battened out and is dead nuts perfect before you start glassing, then be aware that it may not be a step backwards to put a mini-grinder into a spot like that, make it a low spot and treat it like a repair before you get onto fairing the rest of the deck.

A 3/16ths lump is a long way out of fair if you put it in the wrong spot, if the rest of the panel is pretty close.
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Old 27-06-2016, 08:27   #11
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Re: Fiberglass cloth weight

Thanks Zach, So what you are saying is to grind the plywood along the deck and cabin side about 1/16" to 1/8"deep and out about 2", coat with epoxy, lay in 1708 cloth, grind until only the recessed glass is left and add the fillet?
When you have the 2" wide 1708 at each seam do you butt the layer of cloth on top or lap it?
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Old 28-06-2016, 08:49   #12
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Re: Fiberglass cloth weight

You got it...

Once you have the tape glassed in, you sheath right over it as though it isn't there with cloth.

Just double check while you are grinding after glassing in the tape with both a straight edge, ("Paint stirrer with a good edge") vertically that it is either perfectly flat or just a touch low with a batten that it is fair along its length before glassing.

If you are going to be painting by hand and not spraying... My recommendation is to make the decorative fillet you pull after sheathing the boat in cloth... large enough that a Wizz foam paint roller fits. Those things work quite well for rubbing primer into pin holes in fillets, at least until they swell up and start to disintegrate... but the fillet has to be large enough that the end can fit.

If you go small with the fillets, you have to brush the fillets, and that takes a bit more time.

Do you know what kind of paint you are going to finish the project with?

More time, less money:

I like to epoxy coat everything a few times with neat resin if you are going with Interlux bright sides or perfection, as the primers offer next to no build thickness. You can get close to perfect with epoxy coating, and then prime once, paint once.

More money, More money...
If you are going Awlgrip or Alexseal I like to use their primers as they build quick and sand like butter...

Down and dirty:
If you are going with an enamel Oil base top coat, I use Sherwin Williams Tile Clad Epoxy as a high build primer, as it is touch enough that once you are fair you can sand back and scuff off without burning back to glass.
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Old 28-06-2016, 09:32   #13
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Re: Fiberglass cloth weight

"If you are going to be painting by hand and not spraying... My recommendation is to make the decorative fillet you pull after sheathing the boat in cloth... large enough that a Wizz foam paint roller fits. Those things work quite well for rubbing primer into pin holes in fillets, at least until they swell up and start to disintegrate... but the fillet has to be large enough that the end can fit."

I was planning on making the fillets after coating the ply with several coats of epoxy. Then cloth over. It sounds like you do the fillets at the end?

I'm also planning to spray, although there will be places like where the cockpit coaming gets close to the bulwark that will be difficult to spray. I plan to glass the aft end of the boat prior to building the box coamings. Should I rout out two inches beyond the coaming sides to later glass them in?

Minaret, sounds like three layers is the way to go. For materials I estimate +- 600 sq/ft of area for a 40' x 12' max beam, cabin sides and bulwark. I was going to order 15 gal. of epoxy to start and 15 gal of the fairing compound. Have not yet figured the fillet amount, but I will be using all System Three products. Do those amounts seem reasonable?
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Old 28-06-2016, 14:55   #14
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Re: Fiberglass cloth weight

I do two stages... The first is a small fillet the radius of the air roller... Then once the cloth is on and sanded smooth, a second of soft stuff either Awlgrip Awlfair or West Systems 410 that go on before primer.

Just don't use System Three's quick fair... That stuff is grainy and not my favorite.

Cheers,

Zach
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Old 16-05-2017, 16:05   #15
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Re: Fiberglass cloth weight

Well, after nearly a year I am through the first pass sanding of the 407. Nothing happens fast. I laminated three layers of 10oz cloth and west system. On the cabin top, sides and coamings I used peel ply with the help of my son.Great stuff once you learn how to lay it down. Once he went back to school I skipped the peal ply and used 407 mixed like ketchup to fill the weave on the remaining areas.
I used a long board to get down to the cloth over laps and used them as a guide in most places. I added a second coating of 407 to the low spots on the cabin top and sides. I'm wondering if I should use 410 for easier sanding on the rest of the boat. also, I circled the low spots with a pencil and then hit those areas with 60 grit to scuff up. I'm wondering if I need to scuff as it adds a bit of time? My assumption is yes. I have stayed away from the inside corners for now and plane to touch them up towards the end.

I plan to use Awlgrip 545 and either Awlcraft or Awlgrip. with their non skid product. I used a long board on the deck and cabin top where most of the nonskid will go. I'm wondering if I can use a DA festool 150 to work the second round? Reading another recent thread it sounds like the nonskid will hide some imperfections.
Thanks, Bill
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