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Old 02-03-2021, 21:43   #1
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How many layers fiberglass on new deck

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!
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Old 02-03-2021, 21:51   #2
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Re: How many layers fiberglass on new deck

Three layers of 1708 biax would be easier to wet out, use less resin, and be stronger (the mat is included). Maybe 0.1" thick.


How thick depends on the span and the core. Match what was there, or perhaps a little less with biax.
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Old 02-03-2021, 21:58   #3
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Re: How many layers fiberglass on new deck

Quote:
Originally Posted by theglo View Post
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!
Instead of starting from scratch with that layup I cut out the old deck in large areas, then recore the area and replaced the old deck section.

This blog entry has some photos of the process. I've done several over the years. <Wingssail Images-Cruising Photos from Around the Pacific>
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Old 02-03-2021, 22:04   #4
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Re: How many layers fiberglass on new deck

I did that on my last go around and had really bad luck getting the old glass to adhere properly to the new core.

I was admittedly very new to all things boating at the time and did a poor job.

I added a top layer of glass over the old deck after rebedding it which at this point has likely rendered all of it trash.

These areas are now my biggest problems.
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Old 02-03-2021, 22:05   #5
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Re: How many layers fiberglass on new deck

I'll take a look at the 1708. Looks promising.
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Old 02-03-2021, 23:44   #6
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Re: How many layers fiberglass on new deck

Quote:
Originally Posted by theglo View Post
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!

So you are using polyester resin ?
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Old 03-03-2021, 00:15   #7
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Re: How many layers fiberglass on new deck

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Originally Posted by boatpoker View Post
So you are using polyester resin ?

I've never used vinyl ester but maybe that would be better than polyester for this type of work?

https://www.thoughtco.com/vinyl-este...-resins-820376


WHICH RESIN TO USE?? EPOXY vs. POLYESTER vs. VINYLESTER

More than 95% of all boats, truck & car bodies made of fiberglass are made primarily of E-glass, an orthothalic polyester resin and isothalic polyester gelcoat.
Therefore, items constructed with these materials should be repaired with the same or compatible material. LBIís 301 orthothalic polyester resin is a good choice for most repairs. It provides a chemical bond to the existing laminate with similar strength & flexural characteristics.
Ortho polyester, isothalic polyester and vinylester resins are compatible, they all have styrene (commonly known as the ďfiberglass smellĒ) and chemically bond to one another.
When higher strength, bond and water resistance is required (such as keel, rudder repair, or out-board transom replacement) use LBIís 302 Isothalic Polyester Resin.
To achieve the highest bond strength and water resistance use LBIís 901 Vinylester Resin.

Vinylester is essentially a styrene modified epoxy resin. It adds excellent strength, rigidity, adhesion, water and chemical resistance.
KEEP IN MIND
  • Epoxy adheres to wood much better than polyester does. To cover wood, a laminate using epoxy resin and 10 oz, cloth will yield a much better job than 10 oz. cloth and polyester resin. The epoxy/cloth laminate is comparable to using polyester resin with 3/4 oz. mat and 10 oz. cloth however the epoxy laminate requires much less labor to fair.
  • A polyester laminate job is somewhat less expensive in material costs than an epoxy laminate project of the same size.
REMEMBER
  • Fiberglass mat should not be used with epoxy because the binding material in the mat will NOT dissolve in epoxy resin.
  • Either mat, cloth or woven roving may be used with polyester or vinyester resin.
  • Since mat sticks much better to wood than does cloth, always make mat your first layer against the wood to be covered in a polyester laminate project.
  • We recommend using a layer of mat between layers of cloth for maximum adhesion between layers.
https://www.lbifiberglass.com/which-resin-to-use-epoxy-vs-polyester-vs-vinylester/
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Old 03-03-2021, 00:30   #8
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Re: How many layers fiberglass on new deck

Quote:
Originally Posted by wingssail View Post
Instead of starting from scratch with that layup I cut out the old deck in large areas, then recore the area and replaced the old deck section.

This blog entry has some photos of the process. I've done several over the years. <Wingssail Images-Cruising Photos from Around the Pacific>
What he said!


Quote:
Originally Posted by theglo View Post
I did that on my last go around and had really bad luck getting the old glass to adhere properly to the new core.

I was admittedly very new to all things boating at the time and did a poor job.

I added a top layer of glass over the old deck after rebedding it which at this point has likely rendered all of it trash.

These areas are now my biggest problems.
What core did you use? Did you use epoxy?
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Old 03-03-2021, 04:27   #9
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Re: How many layers fiberglass on new deck

First of all, I'd use vinylester. And second the idea of 1708. If you use three plies of it mat down, then the last ply mat up, that upturned mat will make a nice bed for the final layer of boat cloth. I wouldn't mess with plain mat if I didn't have to--it's messy enough stitched to the biax; by itself it's hard to keep tidy.
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Old 03-03-2021, 05:06   #10
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Re: How many layers fiberglass on new deck

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Originally Posted by Celestialsailor View Post
What he said!



What core did you use? Did you use epoxy?
I used 3/4" marine ply and did not use epoxy. Wish I used epoxy.
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Old 03-03-2021, 05:08   #11
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Re: How many layers fiberglass on new deck

Was planning to use epoxy. I think I've switched to 3 layers of that 1708. Looks simpler.
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Old 03-03-2021, 05:21   #12
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Re: How many layers fiberglass on new deck

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Was planning to use epoxy. I think I've switched to 3 layers of that 1708. Looks simpler.
1708 is for polyester and vinylester. Not epoxy.

Please stop a second and get it figured out before you just buy everything.

I’d forget all those layers for sure. All that matters on a deck is the total weight of glass per square foot or meter or whatever .

How much total weight (ounces) does a dufor have per square foot?

Or grams per square meter if not in USA?

Now find out what biaxial type glass you can get easily, or even triaxial if using epoxy and put down the same weight of it per square foot/meter that you have found the rest of the boat uses. That’s for epoxy. The thicker the glass, the better for not wasting your time. Less layers.

If you do want to go 1708 and polyester or vinylester, do exactly as BenZ said above.

Also, use a real core. Even if you want to keep the budget lean.
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Old 03-03-2021, 05:57   #13
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Re: How many layers fiberglass on new deck



The previous layup start of thread would have been subtotal--> 0.183 inches thickness.

Spreadsheet data derived from the chart from the link below
chart is from Glenn-L, image is from boatdesign.net

https://www.boatdesign.net/threads/f...trength.16928/

I am used to really light layups (think surfboard) so all of this seems monster thick. I will need to wrap my head around thick as I need to fix some fitting-induced cabin top rot on my 21-footer, hoping to go up from the inside as inside is unfinished and outside gel coat is relatively intact.
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Old 03-03-2021, 06:06   #14
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Re: How many layers fiberglass on new deck

I also agree with Spot. I have a single layer of 34oz triax on my deck, hulls. That’s it, other than sppecific reinforcement areas.

The laminate schedule seems insane to me.
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Old 03-03-2021, 06:06   #15
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Re: How many layers fiberglass on new deck

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Originally Posted by Chotu View Post
1708 is for polyester and vinylester. Not epoxy. ...

Incorrect. Unlike most mat, 1708 does not use binder that needs to be dissolved by the resin. In addition to many other projects, I built a pair of hull extensions on my PDQ using 1708 using epoxy. No problems at all.


I've used this with epoxy, polyester, and vinyl ester. I'm going to avoid this part of the debate. All three will work equally well with 1708.


I think some assume plywood as a core will make it stronger. In fact, the plywood is weaker in shear than end grain balsa, so the result is often weaker. It also rots faster, because it wicks the water crosswise much faster than balsa. Finally, bonding is more difficult because it does not conform as well. So yes, use a real core material.
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