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 “DB”), built from two layers of 8.5-oz./sq. yd. uni-di (totalling 17 oz./sq. yd.—the “17”), 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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