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Old 03-03-2021, 19:35   #61
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Re: How many layers fiberglass on new deck

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Originally Posted by thinwater View Post
I did not explain because I thought that was a known thing. It's right on the page. The mat is very, very thin.

https://www.jamestowndistributors.co...ct-detail/1441


You forgot to look at the REST of the Jamestown page. LOL. Says I was right all along.

Here is the copy/paste from the page you linked to. Open “Info and guides” for the actual weights of 1708

“ 1708 signifies the weight of each layer.
+/- 45 biaxial weave cloth is 17 ounces per square yard.
mat backing is 8 ounces per square yard
yields a total weight of 25 ounces per square yard”

Go back to your link and check. Building anything except small repairs with 1708 and epoxy is a HUGE mistake and extremely poor engineering.

It’s 1/3 heavier and untold amounts of wasted epoxy.

It was invented ages ago for polyester.
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Old 03-03-2021, 21:11   #62
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Re: How many layers fiberglass on new deck

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So back to the 17,000lbs boat. Well, it’s now 25,000lbs because you used 1708 instead of 17oz biax. 8000lbs of additional weight!! 1/3 of the weight unnecessary. And worse yet, let’s look at the money wasted. 4000 lbs of epoxy or close to 100 gallons. That’s $6000 wasted in epoxy to be 8000lbs overweight. Yikes!!!
A 17,000 lb boat is a bit more than fiberglass. Ballast, hardware, engine, etc add up to a great deal more than the fiberglass portion.

Most fiberglass boats in the world were built with alternating layers of roving and mat. The op's Dufour could be as well. As I posted he has to get the repair section to be about as thick as what was already there. Yes, he could use biax by itself but the 1708 will probably be stronger than original and will get to the correct thickness with less layers.

The op is asking about a repair, not how to build a complete boat. 1708 is easy to use, forms over curves and corners easily, and works well for repairs.

I have used it for years and had no issues, no failures for small repairs such as glassing over old thru hull holes or for glassing in bulkheads where it forms the shape necessary easily. Don't see a need to change what works.
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Old 04-03-2021, 03:02   #63
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Re: How many layers fiberglass on new deck

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Originally Posted by mitiempo View Post
A 17,000 lb boat is a bit more than fiberglass. Ballast, hardware, engine, etc add up to a great deal more than the fiberglass portion.

Most fiberglass boats in the world were built with alternating layers of roving and mat. The op's Dufour could be as well. As I posted he has to get the repair section to be about as thick as what was already there. Yes, he could use biax by itself but the 1708 will probably be stronger than original and will get to the correct thickness with less layers.

The op is asking about a repair, not how to build a complete boat. 1708 is easy to use, forms over curves and corners easily, and works well for repairs.

I have used it for years and had no issues, no failures for small repairs such as glassing over old thru hull holes or for glassing in bulkheads where it forms the shape necessary easily. Don't see a need to change what works.
Of course. I’m illustrating a point only. For the OP 1708 is great. It’s a small repair. Mat as the last layer facing up makes it easier to smooth out. Good stuff. BUT... the misinformation in this thread was ridiculous. Had to be corrected with links and a little illustrative math.

Bottom line is you are wasting 1/3 of the weight you add and 1/3 of your epoxy if you use 1708 instead of 17oz biax. And that really needed driving home due to all the people in this thread not understanding what 1708 is or why we don’t use it with epoxy in boat building.

Repeating the facts: 1708 isn’t used with epoxy because the mat layer is all wasted material. It provides no strength (the biax part of 1708 provides the strength) and the mat, making up 1/3 of the 1708, is just wasted material and wasted weight.

Just don’t want anyone new to this stuff reading all the incorrect info in this thread and going off to build a boat out of 1708 and ruining their project.

Sorry, OP. Ignore my input. You’re fine doing a deck repair this way as long as performance to weight ratios aren’t something you’re after. It’ll be ok for that purpose.
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Old 04-03-2021, 03:56   #64
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Re: How many layers fiberglass on new deck

Funny how people ignore the ones who actually use and know the material.

The 1708 I use has a 17 ounce biax plus a 3/4 ounce mat and all that stitched together. I think the 0 in 1708 means 0.8 ounce.

Just to confirm, here is the material from my source: https://fiberglassflorida.com/1708-biax.html
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Old 04-03-2021, 03:58   #65
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Re: How many layers fiberglass on new deck

Style DBM 1708 contains a double bias (17oz) stitched at 45 degrees along with one layer of 3/4oz mat. The thickness is approximately 0.044. This material is compapatible for use with polyester resine, epoxy resin and vinyl ester resin. If you need full rolls, see the full roll item.
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Old 04-03-2021, 04:56   #66
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Re: How many layers fiberglass on new deck

The confusion may come from CSM being typically called out as oz per sq ft and cloth as oz per sq yd. See listing below from Totalboat, they do both. Days like these grams per square meter would be so much easier...

https://www.totalboat.com/product/17...erglass-cloth/

17 Oz. Biaxial Fiberglass Cloth

$10.99 – $184.66
#1708 E-glass biaxial (+/- 45 degree) fiberglass cloth with 3/4 oz. mat backing, ideal for tabbing, reinforcing, and repairs.

Description

Biaxial fabric consists of two layers stitched together, with their fiber strands lying at +/- 45 degrees to the edges (instead of along the roll and across at 90 degrees, as with plain weave fiberglass fabrics). “1708” indicates the weight of each layer. For example, the +/- 45 biaxial weave cloth is 17 oz. per square yard, and the mat backing is 8 oz. per square yard, so the total weight is 25 oz. per square yard.
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Old 04-03-2021, 05:18   #67
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Re: How many layers fiberglass on new deck

Interesting... Lot's of conflicting info online about 1708, what a surprise.

Well, I just went and examined a sample of 1708 I have, sorry Choto, no way is the mat half the weight of the biax. I didn't peel them apart and weigh them, but the mat is clearly very thin. Take a look for yourself.
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Old 04-03-2021, 11:49   #68
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Re: How many layers fiberglass on new deck

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Interesting... Lot's of conflicting info online about 1708, what a surprise.

Well, I just went and examined a sample of 1708 I have, sorry Choto, no way is the mat half the weight of the biax. I didn't peel them apart and weigh them, but the mat is clearly very thin. Take a look for yourself.
I agree. The 1708 I have and use has a very thin light layer of mat. 3/4 oz a square yard seems correct looking at it.

-----------------------------------------------------------------------------------------------from Chotu:
Repeating the facts: 1708 isn’t used with epoxy because the mat layer is all wasted material. It provides no strength (the biax part of 1708 provides the strength) and the mat, making up 1/3 of the 1708, is just wasted material and wasted weight.
--------------------------------------------------------------------------------------

Mat doesn't add very much strength to any application, any resin. That was never its purpose.
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Old 04-03-2021, 11:53   #69
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Re: How many layers fiberglass on new deck

I dont have any at hand as were out in the Bahamas at the moment... who has some 1708 and a scale? Weigh a piece, then peel off the mat and weigh again...
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Old 04-03-2021, 12:14   #70
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Re: How many layers fiberglass on new deck

Flexural strength of stitchmat DBM1708 is 63,000 psi. Standard e-glas fab-mat woven roving is just 30,000 psi. Add to that if you do just biax it will be more brittle than if you are using mat/biax (i.e. stitch mat). The mat is there to provide a good laminar bond between the biax layers. in 1708 the 08 mat is .75oz per sq foot. The mat is NOT wasted material. Nor is it that heavy.

Read Gerr's Book!!
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Old 04-03-2021, 12:23   #71
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Re: How many layers fiberglass on new deck

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Originally Posted by Scubaseas View Post
Flexural strength of stitchmat DBM1708 is 63,000 psi. Standard e-glas fab-mat woven roving is just 30,000 psi. Add to that if you do just biax it will be more brittle than if you are using mat/biax (i.e. stitch mat). The mat is there to provide a good laminar bond between the biax layers. in 1708 the 08 mat is .75oz per sq foot. The mat is NOT wasted material. Nor is it that heavy.

Read Gerr's Book!!
and completely irrelevant to the OP's query.
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Old 04-03-2021, 12:30   #72
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Re: How many layers fiberglass on new deck

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and completely irrelevant to the OP's query.
With all due respect Sir, Gerr's book is exactly what the OP should be reading. It would correctly address all his questions and the discussions that have followed from that.

You have someone advising using pure uni or biax which is not a good idea as it tends to crack up.

The OP asked"
Quote:
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!
Gerr's Book "The elements of Boat Strength for Builders, Designers and Owners" exactly answers all of these questions.
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Old 04-03-2021, 13:00   #73
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Re: How many layers fiberglass on new deck

OK, folks. Everyone else is wrong but you couple people right? Jamestown distributors? Clueless, right? They don’t know what they’re selling. Total boat? Clueless right? Me? No idea. Right? The two or three people here who don’t know what they are talking about. You guys are the experts right?

A square yard of 1708 weighs 25 ounces. Cut it out. Drop it on a scale. Learn.

1708. Where do you think the numbers come from? 17 is the biax. 08 is the mat. Those are weights. In ounces per yard.

How can you even come on here and argue something that is just fact? This is absolutely ridiculous.

I think the craziest part, is not knowing what you’re talking about, and then saying that everyone who sells 1708 doesn’t know what they are selling.

Jamestown distributors is one of the most knowledgeable groups of people selling marine supplies on earth. Yet, you are right and they are wrong.

Starting to make notes here to make sure I don’t listen to any of you guys about other things that I might ask on the form. Because if you can get something so simple as this wrong and argue the hell out of it, what other bad advice are you giving?
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Old 04-03-2021, 13:01   #74
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Re: How many layers fiberglass on new deck

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Originally Posted by Scubaseas View Post
With all due respect Sir, Gerr's book is exactly what the OP should be reading. It would correctly address all his questions and the discussions that have followed from that.

You have someone advising using pure uni or biax which is not a good idea as it tends to crack up.

The OP asked"

Gerr's Book "The elements of Boat Strength for Builders, Designers and Owners" exactly answers all of these questions.
Biax and epoxy cracks up?

Clueless.

I guess this isn’t a boat building forum, but I would hope people had even just a basic concept of how materials and Boat construction works. Wow. I am just shocked.
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Old 04-03-2021, 13:02   #75
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Re: How many layers fiberglass on new deck

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Originally Posted by Scubaseas View Post
Flexural strength of stitchmat DBM1708 is 63,000 psi. Standard e-glas fab-mat woven roving is just 30,000 psi. Add to that if you do just biax it will be more brittle than if you are using mat/biax (i.e. stitch mat). The mat is there to provide a good laminar bond between the biax layers. in 1708 the 08 mat is .75oz per sq foot. The mat is NOT wasted material. Nor is it that heavy.

Read Gerr's Book!!
Clueless


Yet another one who thinks Jamestown distributors and everyone who sells 1708 doesn’t know what they are talking about.

How does a square yard of 1708 weigh 25 ounces then? Can you answer that? Simple arithmetic

As to the wasted material, do you not even understand the concept of directional forces? None at all? Tell me. Why do you think a chopper gun boat is a piece of junk? Go ahead . Answer that one. It will help clue you in as to why directional fibers do all of the work in 1708.


Frankly, this thread scares the hell out of me. I’m asking for advice on this forum in a lot of boat building areas. Granted, it’s all fit at work because the whole is already built, but still. I’m getting some good stuff, but to see something this simple completely misunderstood and then have people arguing it to the moon. That’s nuts.
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