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Old 18-05-2016, 08:09   #1
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Small fiberglass job, woven roving & chopped strand mat

Ahoy,

I have a small glass job I need to do on my Bristol 24 sailboat. To strengthen the strbrd chainplate I need to glass in the piece of wood it currently sits on, so some weight is distributed beyond this small portion of the bulkhead.

Here's the thing--I'm using Don Casey's fiberglass repair book as a guide and I'm confused. He says NEVER adhere woven roving to woven roving, as the bond won't be strong, so he suggests a layer of chopped mat in between the two rovings.

A few pages later he goes on to say that epoxy resin is incompatible with chopped strand mat. So, what gives??

I am only doing two layers of glass, very small project.

Do I go Woven roving to woven roving,
or,
Woven roving, chopped strand, woven roving.

Any thoughts are helpful
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Old 18-05-2016, 08:19   #2
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Re: Small fiberglass job, woven roving & chopped strand mat

this explains epoxy and chopped-strand

WEST SYSTEM - Projects - Chopped stand mat & epoxy
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Old 18-05-2016, 08:20   #3
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Re: Small fiberglass job, woven roving & chopped strand mat

Chopped strand mat has much better adhesion qualities than roving, whereas roving is stronger, that's why you should have a layer of CSM between layers of
roving. The easiest solution, if you haven't already purchased your supplies is to buy bi-axial. It comes pre-made with a layer of each.
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Old 18-05-2016, 08:41   #4
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Re: Small fiberglass job, woven roving & chopped strand mat

just use 1708 biaxial. Its mat stitched to 2 layers of fiberglass. much simpler to work with as it's already unitized
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Old 19-05-2016, 08:41   #5
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Re: Small fiberglass job, woven roving & chopped strand mat

bi axile or e glass forget about the woven roving
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Old 19-05-2016, 09:30   #6
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Re: Small fiberglass job, woven roving & chopped strand mat

If using epoxy, the chopped strand mat CSM between rovings must be the one specially formulated for epoxy resin.
I would prefer 4 layers on cloth wet on wet with epoxy resin.
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Old 19-05-2016, 10:15   #7
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Re: Small fiberglass job, woven roving & chopped strand mat

Quote:
Originally Posted by pcmm View Post
just use 1708 biaxial. Its mat stitched to 2 layers of fiberglass. much simpler to work with as it's already unitized
I agree, biaxial is the way to go.
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Old 19-05-2016, 12:04   #8
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Re: Small fiberglass job, woven roving & chopped strand mat

Quote:
Originally Posted by dinghydreams View Post
Ahoy,

I have a small glass job I need to do on my Bristol 24 sailboat. To strengthen the strbrd chainplate I need to glass in the piece of wood it currently sits on, so some weight is distributed beyond this small portion of the bulkhead.

Here's the thing--I'm using Don Casey's fiberglass repair book as a guide and I'm confused. He says NEVER adhere woven roving to woven roving, as the bond won't be strong, so he suggests a layer of chopped mat in between the two rovings.

A few pages later he goes on to say that epoxy resin is incompatible with chopped strand mat. So, what gives??

I am only doing two layers of glass, very small project.

Do I go Woven roving to woven roving,
or,
Woven roving, chopped strand, woven roving.

Any thoughts are helpful
I would not go roving to roving. Nor would I glass roving to the wood. Beyond that I am not completely sure of what you are attempting to do.
Matt will wick well but has little tensile strength. Roving, just insure you roll or squeegee the resin in well.
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Old 19-05-2016, 13:07   #9
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Re: Small fiberglass job, woven roving & chopped strand mat

I love Don Casey, but some of his advice is outdated. Most chopped strand products nowadays are compatible with epoxy. He also says to use "Ajax" brand cleaner to bleach wood because it's mostly oxalic acid, although oxalic acid was removed from Ajax years ago.

For your project, use the 1708 cloth with epoxy, and replace the wood with G10 board.
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Old 19-05-2016, 15:28   #10
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Re: Small fiberglass job, woven roving & chopped strand mat

preparation is important.
a good soaking of bare timber with epoxy
your using woven cloth to strengthen and spread the load.
if you let the first layer dry it needs to be sanded thoroughly before the next layer is applied. if you are working on a flat surface, not the side of the hull (where the whole lot can run off onto the ground or water) 2 or 3 layers of thin woven cloth, once cured, drill holes oversize, tape off underneath and fill holes with epoxy. when cured, drill to the right size for your bolts. follow with a coat of top coat and she'll be right till next time someone decides to moor a dinghy off the chain plate instead of the bollard
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Old 19-05-2016, 19:31   #11
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Re: Small fiberglass job, woven roving & chopped strand mat

I'm not sure I got this right. Is the bulkhead your chainplate attached to originally glassed to the hull? I had a bristol 25 and that's what it's construction was. The chainplate came down and bolted through the glass...that held the bulkhead to the hull and gave the hull support...and the wood bulkhead. the glass was on both sides of the bulkhead, with a backing plate on the opposite side. that wood bulkhead is not all that holds that chainplate, it's the glass that is attached to the hull that holds the chainplate. the pull is distributed down the hull the bulk head stops the hull from flexing inboard. It's not the adhesion to the wood that need to be so strong, but the adhesion to the GRP hull, where the most force is. if the wood was water damaged, then replace the wood and glass it in the way bristol designed it. I can understand not wanting to replace a whole bulkhead. cut out the affected wood and epoxy in a new peace, keeping in mind that it's job is to hold the hull out. Then glass the outer edge and a foot or so down to the hull with 1.5 oz mat and woven or a layer of Bi- axial with polyester resin. Laying up with epoxy won't the bond enough to warrant the extra expense. polyester adheres well to polyester. which is what the boat is made of. No need to reinvent the wheel.
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Old 22-05-2016, 23:03   #12
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Re: Small fiberglass job, woven roving & chopped strand mat

In my life I've probably wetted out a couple miles of RSM. At least my knees feel like it. I've had no problem with any brand RSM and West Systems. The epoxy does break the bonds holding the strands together. But, using enough epoxy early will get it wetted w/o any real movement of strands. Some other epoxies don't work as well. Polyester wets a little better, but doesn't stick to anything. Buy good rollers.
My boat is wood with fiberglass decks over plywood. When I bought it, the fiberglass w/poly was only holding in about 30% of the area. On one side I pulled up about 65' with one pull.
The reglass job used 2 full rolls of 2.0 RSM and I had no problems getting the strands wetted. And I'm old.
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Old 22-05-2016, 23:19   #13
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Re: Small fiberglass job, woven roving & chopped strand mat

"Then glass the outer edge and a foot or so down to the hull with 1.5 oz mat and woven or a layer of Bi- axial with polyester resin. Laying up with epoxy won't the bond enough to warrant the extra expense. polyester adheres well to polyester. which is what the boat is made of. No need to reinvent the wheel."

Do Not use polyester resin to bond to old polyester resin, use epoxy. Polyester makes weak secondary bonds. Grind the polyester surface and use epoxy.
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