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Old 04-03-2021, 22:40   #91
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Re: How many layers fiberglass on new deck

If you are quoting Gerr you left out the beginning of that chapter/paragraph (my highlighting).

"The second problem with uni-di fabric styles is that there is no mat between the layers to ensure a good interlaminar bond. If great attention to detail is used and if the hull or component is vacuum-bagged in a high-elongation, gap-filling resin system, this can work. For most applications, however, some mat is desirable. This, again, is a delicate balance. First, mat is comparatively weak and heavy, so you want to use as little as possible. Second, many mat products are not compatible with high-strength resin systems. To solve this difficulty, glass manufacturers make fabric styles that are bi-axial with a light or thin layer of mat stitched to it. These are known as stitch-mat styles. A typical stitch-mat is Hexcel Knytex DBM1708. This is a +45, −45 bi-axial (the ďDBĒ), built from two layers of 8.5-oz./sq. yd. uni-di (totalling 17 oz./sq. yd.óthe ď17Ē), with a single..."

Gerr, Dave. The Elements of Boat Strength: For Builders, Designers, and Owners . McGraw-Hill Education. Kindle Edition.

While I respect both Chotu and Boatpoker I just don't happen to agree with them wholly here. So forgive my opinions please. I do agree with using biax stitch mat and personally I would use vinylester for this deck repair. If I had to fill the laminate to make it thicker I would use coremat or CSM or whatever I had most of on hand. I would look at what the laminate schedule is now and either duplicate or exceed that in strength or more than likely use 1708, 1808, 1708 and a CSM veil as a final coat if it matches up to what Gerr advises. I would weigh both cloth and resin to get a good glass to resin ratio but what do I know? I'd also clean the existing deck with MEK or acetone before grinding and add 5% to 10% styrene to a light bond/tack coat before gluing down the core with a vinylester bonding compound. I don't need Gerr to support this decision. I can just say I've done this for years so it's good. Which seems a favorite form of logic on these forums (present company excepted). As an aside I actually have been fixing holes in fiberglass commercial boats (4 dive shop skiffs) for over 15 years now. Everything from big holes to t-boned hulls to delamination from too much wave jumping with 1200# of scuba tanks on board to the transoms being ground off from parking the boat on the beach and literally grinding off the last 4" of the hull/transom area. So yes I have put on well over 100 gallons of resin and many yards of various cloths/reinforcements over the years. But I followed Gerr's and others advice when I did so. Not saying Gerr is the only right answer but neither is some of the advice offered here so far either. There's a lot of ways to fix a boat, some right, some not so much.

If you can get the deck off and save it you probably had problems in the past from a dry joint. If you "prime" the core with a thinned resin, say 5% styrene, let it set up some and then put bonding compound on it you may get better results. Ditto the underside of the deck piece with this same "primer". You want to use laminating resin for any of this work if using vinylester. Vinylester is stronger (it's about as strong as epoxy) than the polyester resin that is there now and will chemically bond to old polyester if it's clean and prepped properly. If using balsa core liberally apply resin and make sure your bonding compound is fresh. Balsa really sucks up resin. There is tons of YouTube videos on this kind of repair. If you are going balsa and laminating a new deck prime the balsa and apply a heavy coat of resin and then apply a pre-saturated layer of stitch mat, csm side down as you tie layer from core to laminate.

I would question why one needs a high tech, ultralight weight epoxy repair on a wet Dufour deck. Why does it have to be as light as possible? Why not use biax? It's cheap, easy to work with and uses a lot less resin than what was originally offered up for comment. If the OP has issues with his previous repairs is going with uni or bi-directional alone and epoxy really the way to go? While I applaud Chotu building an ultra light, ultra fast boat I am not sure that is what is called for here.

I would also ask why is there a water leak into the cabin that seems to be related to a "large" delaminated "soft" deck. Which to me seems like something is bending a lot more than it was designed to be doing. Which makes me think there is literally a compromised structural element involved. Yes a skinned deck is a structure in my book. But I'm clueless which is why I suggested reading Gerr. I admit boatpoker is probably right in that it's a simple deck repair. Or is it? Hard to say from the original post. Any reason NOT to try and duplicate or surpass the original layup? He's going to have to order core, resin, bonding compound anyway. So why not order 1708 and 1808 and some tools like spreaders and bubble busters etc. instead of just straight e-glass at the local hardware store? Is 4 to 5 layers of whatever the local store has in eglass as strong as the original laminate? Or to fix the "large" soft spots? The OP would know by just looking it up on one of the many easy to read tables in Gerr's book.

Would it hurt to have the knowledge in Gerr's book which it seems boatpoker has not read? It's not a technical tome like you suggested I needed to read. It's a well written, easy to understand reference book that would answer all the OP's questions. I can't imagine how him reading Gerr's book would in anyway be counter productive. Just by the nature of his question I would venture a WAG that the OP could benefit from spending $21 and taking an hour or so to read up on his project.

The OP wanted an opinion as to if what he planned would be sufficient. I offered my opinion and suggestions. Can't help it if you two don't agree with it.

For supplies I would look at USComposites and LBI Fiberglass both of whom I have used and appreciate. There are many others out there.
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Old 05-03-2021, 04:54   #92
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Re: How many layers fiberglass on new deck

Thatís cool, I added the Kindle version of Dave Gerrs book to my library. It sits right next to Brian Tossís Riggers Apprentice. I love how these books become available on Kindle so we can offload the weight of paper books, while being able to look something up with a tap of a finger
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Old 05-03-2021, 05:56   #93
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Re: How many layers fiberglass on new deck

Yes, Choto is right, it is about 24 oz/yd. I weighed a sample.


But, the assertion (rant?) that mat adds no strength is incorrect. Chopper gun stuff is a poor comparison because it is not rolled with layers of woven product. However, mat is still glass, when rolled the fibers are in the plane, and they improve contact between the layers and provide off-axis strength to roving and cloth when there are only a few layers, all with the same orientation. This is particularly obvious when break testing cored panels with point loads and off-axis loads (like wood, they break according to the grain). Mat is not perfect, but I wouldn't build a whole boat with uni either.

Bottom line: The product has proven itself useful in a certain applications. No product is all-purpose.
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Old 05-03-2021, 06:01   #94
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Re: How many layers fiberglass on new deck

Mat definitely adds some strength, just not nearly as much as an equal weight of other fabrics. As an example, the original bow pulpit construction on my boat was mostly or entirely mat from what I can tell. But it was 1/2" thick on top, 3/8" thick on the bottom with an inch of plywood in the middle. So while it's very heavy relative to its strength, it's certainly strong enough for the loads it needs to handle.
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Old 05-03-2021, 16:23   #95
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Re: How many layers fiberglass on new deck

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Originally Posted by mitiempo View Post
Did it ever occur to anyone that there could well be differing weights of mat on different types of biax?

The biax 1708 I have and use has a very thin layer of mat - way too little to be 1/3 the total weight.
It would be very strange if 1708 from different manufacturers had different weights of mat. Engineers calculate hull weights and resin amounts based on "1708" meaning something definite.

As for mat adding some strength, well, of course it does, but at the cost of a lot of weight compared to longer fibers. Rule of thumb is that fibers become worthwhile for strength purposes when they are 3 inches or longer.
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Old 05-03-2021, 16:41   #96
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Re: How many layers fiberglass on new deck

I am still in shock that a manufacturer believes that 1/4 '' of fiberglass at the V of the keel/hull is plenty . A 1/4 '' Aluminum hull thickness , i believe i read was 10-15 times stronger . I am nervous about fiberglass now .
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Old 06-03-2021, 17:59   #97
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Re: How many layers fiberglass on new deck

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Originally Posted by s/v Jedi View Post
That’s cool, I added the Kindle version of Dave Gerrs book to my library. It sits right next to Brian Toss’s Riggers Apprentice. I love how these books become available on Kindle so we can offload the weight of paper books, while being able to look something up with a tap of a finger
I stupidly bought $50 of Amazon Coins and now I'm trying to find something I can spend it on. Can I buy Kindle books with Amazon Coins? (I would appreciate your advice)
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Old 06-03-2021, 18:12   #98
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Re: How many layers fiberglass on new deck

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Originally Posted by coopec43 View Post
I stupidly bought $50 of Amazon Coins and now I'm trying to find something I can spend it on. Can I buy Kindle books with Amazon Coins? (I would appreciate your advice)
I donít know what Amazon coins are.
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Old 06-03-2021, 19:28   #99
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Re: How many layers fiberglass on new deck

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I donít know what Amazon coins are.

I bit of research:
NOTE: Kindle books are not eligible for purchase using Amazon Coins.14 June 2019

Amazon Coins are a digital currency valued at one US cent per coin. You can buy them through the site, and Amazon Coins can be used to purchase games and apps. Amazon Coins don't expire, but you can only use them on Fire tablets and TVs, or via the Android-compatible Amazon Appstore.10 Mar 2020


I'll spend them on something just so Bezos doesn't end up with them
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Old 07-03-2021, 03:11   #100
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Re: How many layers fiberglass on new deck

Finishing up my obligation to not have incorrect factual information on the thread, the person who said mat doesn’t have binders and is 100% compatible with epoxy is wrong too.

https://support.jamestowndistributor...h-epoxy-resin-

You can use 1708 with epoxy (I have a roll of it for doing finish work and had planned to use it with epoxy to get some smooth surfaces), but it’s both excessively heavy for the strength it delivers and doesn’t bond quite as well as straight biax cloth would, as seen in the Jamestown tech support article above.

These are important facts about the materials, not opinion, so they shouldn’t be glossed over by the loudest chorus of voices instead of the correct information.

It’s vital anyone working on large projects understand these materials, rather than listen to opinion because not only might they ruin a project, but in some cases a life might depend on it.

1708 was developed ages ago as a bulking/laminating material for use with polyester resin. It is not the correct choice for use with modern epoxy resins in structural applications , even though you can get away with it.


Note: Mat is just a dry chopper gun laminate, held together with styrene soluble binders that you add resin to. Same as those chopper gun boats everyone bashes on. So don’t get too excited about it. It’s a bulking layer. A smoothing layer. Not a strength layer in comparison to cloth/epoxy.
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Old 07-03-2021, 03:32   #101
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Re: How many layers fiberglass on new deck

You are fully correct. Mat relies on the binders to be dissolved by solvents like Styrene, which standart formulations of Epoxy do not have.

Mat is great for laying up complex shapes at low cost with Polyester. Once the binders are broken the, now in the resin suspended, fibers align easily with the surface.
So, a light mat with short fibers is for example great to laminate a complex dashboard.

As the fibers are fairly short in mat they are not as good at load bearing as the continuous fiber strands in woven or the (even better) multi axial stitched materials.

Lightly stitched materials in multiaxials allow the continuous fibers to align more easily with the mould surface than woven materials.

There are special mat types which are stitched instead of having binders which can be used with Epoxy or Vinylesters. They are used in special circumstances, for example in infusion or when you want better interlaminar shear properties in a laminate.
Mat is slightly better than woven and multiaxials in this respect, which is why one tends to sometimes use mat between layers of woven or multiaxial layers.
Quote:
Originally Posted by Chotu View Post
Finishing up my obligation to not have incorrect factual information on the thread, the person who said mat doesnít have binders and is 100% compatible with epoxy is wrong too.

https://support.jamestowndistributor...h-epoxy-resin-

You can use 1708 with epoxy (I have a roll of it for doing finish work and had planned to use it with epoxy to get some smooth surfaces), but itís both excessively heavy for the strength it delivers and doesnít bond quite as well as straight biax cloth would, as seen in the Jamestown tech support article above.

These are important facts about the materials, not opinion, so they shouldnít be glossed over by the loudest chorus of voices instead of the correct information.

Itís vital anyone working on large projects understand these materials, rather than listen to opinion because not only might they ruin a project, but in some cases a life might depend on it.

1708 was developed ages ago as a bulking/laminating material for use with polyester resin. It is not the correct choice for use with epoxy in structural applications , even though you can get away with it.
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Old 07-03-2021, 03:48   #102
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Re: How many layers fiberglass on new deck

Quote:
Originally Posted by Franziska View Post
You are fully correct. Mat relies on the binders to be dissolved by solvents like Styrene, which standart formulations of Epoxy do not have.

Mat is great for laying up complex shapes at low cost with Polyester. Once the binders are broken the, now in the resin suspended, fibers align easily with the surface.
So, a light mat with short fibers is for example great to laminate a complex dashboard.

As the fibers are fairly short in mat they are not as good at load bearing as the continuous fiber strands in woven or the (even better) multi axial stitched materials.

Lightly stitched materials in multiaxials allow the continuous fibers to align more easily with the mould surface than woven materials.

There are special mat types which are stitched instead of having binders which can be used with Epoxy or Vinylesters. They are used in special circumstances, for example in infusion or when you want better interlaminar shear properties in a laminate.
Mat is slightly better than woven and multiaxials in this respect, which is why one tends to sometimes use mat between layers of woven or multiaxial layers.
Just a quick comment: vinylester will break down the mat binders--as far catalyzing and use it works exactly the same way as polyester. I often mix vinyl with poly when transitioning from a surface that needs vinyl to one that can be laid up with normal polyester.
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Old 07-03-2021, 04:16   #103
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Re: How many layers fiberglass on new deck

Correct.
Quote:
Originally Posted by Benz View Post
Just a quick comment: vinylester will break down the mat binders--as far catalyzing and use it works exactly the same way as polyester. I often mix vinyl with poly when transitioning from a surface that needs vinyl to one that can be laid up with normal polyester.
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Old 07-03-2021, 07:18   #104
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Re: How many layers fiberglass on new deck

Quote:
Originally Posted by Chotu View Post
Finishing up my obligation to not have incorrect factual information on the thread, the person who said mat doesnít have binders and is 100% compatible with epoxy is wrong too.

https://support.jamestowndistributor...h-epoxy-resin-

You can use 1708 with epoxy (I have a roll of it for doing finish work and had planned to use it with epoxy to get some smooth surfaces), but itís both excessively heavy for the strength it delivers and doesnít bond quite as well as straight biax cloth would, as seen in the Jamestown tech support article above.

These are important facts about the materials, not opinion, so they shouldnít be glossed over by the loudest chorus of voices instead of the correct information.

Itís vital anyone working on large projects understand these materials, rather than listen to opinion because not only might they ruin a project, but in some cases a life might depend on it.

1708 was developed ages ago as a bulking/laminating material for use with polyester resin. It is not the correct choice for use with modern epoxy resins in structural applications , even though you can get away with it.


Note: Mat is just a dry chopper gun laminate, held together with styrene soluble binders that you add resin to. Same as those chopper gun boats everyone bashes on. So donít get too excited about it. Itís a bulking layer. A smoothing layer. Not a strength layer in comparison to cloth/epoxy.
All true but he's not building an entire boat. He's fixing a wet deck on a polyester/chopper, mat and roving built boat. Saving weight in this application may be an interesting academic exercise but hardly critical to the repair.

You make a good argument to use an ester resin to fix an ester resin built boat. Vinylester resin is what most professionals use to repair polyester laminated boats. It will chemically bond to polyester (epoxy won't), is water proof, is cheaper than epoxy and is almost as strong as an epoxy. Vinylester is a styrene modified epoxy. Vinylester is much stronger than the polyester the boat is built with while epoxy is stronger than vinylester.

Biaxial stitchmat like 1708 will bond perfectly well to itself and existing laminate if you use poly or vinylester resin. Funny that every epoxy maker website I look at has biax stitchmat listed as a laminate material and none say DO NOT USE biax stitchmat. I get your whole rant about weight and use only uni or biax, !!no mat ever!! (thank you Joan Crawford) but does it apply to the OP's problem?

Epoxy is great stuff but if you are repairing a polyester boat epoxy resin may not be the best choice. Epoxy is a great choice for a light weight, strong albeit expensive boat construction. Epoxy is great for going over wood or when using Kevlar or Carbon fiber. It's easy to use and forgiving in application. There is no styrene involved with epoxy but I would still pick vinylester resin to repair a polyester boat deck issue. YMMV.

I am sure that no matter what the OP uses, vinylester or epoxy or polyester and if he uses 1708 or not the repair would be just fine. I am sure that if the deck was repaired with epoxy and 1708 it would be stronger than the original laminate on the boat. Sorry but I reject the ONLY way to fix a boat is your way.

There are a ton of epoxy versus vinylester resin threads on the forum.

https://www.lbifiberglass.com/resin-...n-differences/

Cluelessly yours.
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Old 08-03-2021, 12:48   #105
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Re: How many layers fiberglass on new deck

Hi,
Number of layers and core thickness really depends on the size of your deck panel e.g. the length and width to the next support.
With your Dufour you should be fine with:
400g/m2 at 0/90 (fibre direction) on the outside
400g/m2 at +-45 (fibre direction) on the core
20mm core thickness (Pvc or Balsa)
400g/m2 at +-45
400g/m2 at 0/90

Try not to go below 0.9mm of laminate thickness on each skin.
Hope that helps.
Cheers

I'm doing my shopping for our haulout next month. We are replacing a few large areas of the deck that are shot and causing sponginess and water leaks in the cabin. Boat is 45' Dufour.

I'm planning on using this lay up over the new core:

1.5oz mat
24oz woven roven
then
1.5oz mat
24 oz woven roven
and then
10 oz cloth to finish

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![/QUOTE]
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