One more time with reglassing our deck.

[GILow]

Hi Cruisers,

I've asked this one before, and I got very close to a resolution. Of course, time and life got in the way, but I am back to looking at fixing the deck on the boat and I still have one more question.

Background:

The construction of the deck is two layers of half inch ply, supported by deck beams at about 450 mm centers.

The deck is about 24 square meters, free of just about anything except two hatches and a couple of cleats. It is as simple as a deck can reasonably be. No funny curves, no fiddly bits. You can, quite literally, roller skate on it.

Structurally, all is good, but if I don't do something soon it won't be.

The boat is an old, flush deck heavy cruiser, NOT a showboat, which I plan to use for a one to three year cruise in about three years time, mainly around Australia and the warmer bits to the North.

The fiberglass layer is NOT structural, it is simply a moisture barrier.


The Plan:

So, the plan is to remove the existing CSM, which SHOULD be reasonably easy because it is lifting (and leaking). A few test sections came away very easily indeed.

Then, I am planning on an epoxy cover, partly as a result of the last thread I started recommending epoxy over polyester, partly because the style of work combined with my skill set will make this the easier option. Also I am slightly influenced by the better adhesion to plywood, but this is only a minor consideration overall, the current polyester/csm cover has lasted 40 years.

The question:

So, the real question in my mind is what weight of cloth to use?

The PREFERENCE is to try to do a single layer of double bias, due, again, to the limits of my skill-set and the nature of the job. A single layer will be VERY easy, a double layer will be a lot harder. (I cannot work fast enough to get a chemical bond, so I will be committed to sanding between layers if I do more than one layer.)

The initial recommendations I have had from the suppliers range from 265 gsm, to 420 gsm, to my OCD option of 617 gsm.

Weight is NOT a problem, cost of materials is, of course, a consideration.

But is 617 gsm just pointless extra thickness, or will I see some benefit?

Over to you,

Matt

[44'cruisingcat]

I'd go with the heavier glass. It'll be more resistant to accidental damage from dropped winch handles etc

[GILow]

Originally Posted by 44'cruisingcat

I'd go with the heavier glass. It'll be more resistant to accidental damage from dropped winch handles etc

Good logic. So the 617 doesn't feel too heavy to you?

[44'cruisingcat]

Originally Posted by GILow

Good logic. So the 617 doesn't feel too heavy to you?

No. For flat surfaces it will be easy, in double bias it would even conform to shapes pretty well.

On a balsa or foam core, I'd say you'd want quite a bit heavier, but with ply it should be enough.

[GILow]

Hmm. I am interested in your choice of words. You say it should be enough, which reassures me that I am not being excessive.

[44'cruisingcat]

For purely waterproofing, sure. But it's a deck. Gonna cop knocks and bumps.

Definitely not excessive.

Ours is a lightweight boat. But the decks are 1000 GSM. (Not over ply though).

[GILow]

Thank you, that puts a better perspective on it for me.

[Stumble]

First things first I would epoxy seal the entire wooden deck before you put any glass down. Then because you are using epoxy, secondary bonds are fine, you don't have to get the entire thing done before the first layer kicks. You need to wash off the blush between layers, but a good laminating no/low blush epoxy will make this pretty trivial.

[GILow]

Originally Posted by Stumble

First things first I would epoxy seal the entire wooden deck before you put any glass down. Then because you are using epoxy, secondary bonds are fine, you don't have to get the entire thing done before the first layer kicks. You need to wash off the blush between layers, but a good laminating no/low blush epoxy will make this pretty trivial.

Ok, so I think I have been quoted on some "tpda" to thin the epoxy for that first coat on the timber. Does that sound right? Then the supplier suggested I do as much deck with the thinned epoxy that I can subsequently cover with the glass and epoxy before that first coat completely cures. Is this consistent with your recommendation?

[dsiddens]

Hello GILow,

Your description of a deck with two layers of plywood caught my eye: we've recently redecked our boat which has two layers of half inch plywood. We used epoxy, no thinner, and lots of glass. How much glass you ask? Between the layers of ply two layers of 1708. On the weather deck something like four layers of 1708. 1708 is a stitched product of biaxial with chop. We wrapped the weather deck over to the hull. The deck was faired, primed with epoxy primer then top coated with Awlcraft acrylic. For nonskid we used Rustoleum Restore Advanced, a water based acrylic containing grit. When we made any hole in the deck, we made generous chamfers. For bedding I like butyl rubber tape.

Doug

[Stumble]

I can not stress strongly enough how stupid I think thinning a 100% solids epoxy is. No reputable formulator of epoxy recommends it. It absolutly destroys the physical properties and its vapor barrier properties.Worse it does absolutly nothing positive for this loss.

[GILow]

Originally Posted by Stumble

I can not stress strongly enough how stupid I think thinning a 100% solids epoxy is. No reputable formulator of epoxy recommends it. It absolutly destroys the physical properties and its vapor barrier properties.Worse it does absolutly nothing positive for this loss.

Greg, I believe TPRDA is not the same as an acetone based thinner. I won't try to upsell a product I have never used, but I have read a lot about it from people using it (not selling it) and to date I have not found evidence of problems.

I have heard plenty of credible criticism of acetone based thinners used in epoxy. Again, I cannot tell, from my layperson perspective, whether those criticisms are reasonable or not, but certainly the descriptions that go to the molecular level do leave me thinking acetone thinning is counter productive.

I do like the idea of something that penetrates the timber more, I can see the benefit, and in our relatively benign climate I don't anticipate major problems with moisture. The boat spent the first 30 years of its life North of the tropic of Capricorn and South of the equator, then the next ten years closer to latitude 38S before coming here to Adelaide at latitude 34S so it has seen a variety of rainfall and temperatures. Despite this the design is such that it sheds water well, and it rarely, if ever, sees water over the bow.

Matt

[GILow]

Originally Posted by dsiddens

Hello GILow,

Your description of a deck with two layers of plywood caught my eye: we've recently redecked our boat which has two layers of half inch plywood. We used epoxy, no thinner, and lots of glass. How much glass you ask? Between the layers of ply two layers of 1708. On the weather deck something like four layers of 1708. 1708 is a stitched product of biaxial with chop. We wrapped the weather deck over to the hull. The deck was faired, primed with epoxy primer then top coated with Awlcraft acrylic. For nonskid we used Rustoleum Restore Advanced, a water based acrylic containing grit. When we made any hole in the deck, we made generous chamfers. For bedding I like butyl rubber tape.

Doug

Thanks Doug, great description. I looked at the 1708 early on, but from my reading it would have been difficult for me to work with, I am just not great with fibreglass.

Interesting that you have a layer of glass between the layers of plywood. Ours was not built with that extra layer. There has been no problems with it so far, so I guess I will leave well alone.


Matt

[44'cruisingcat]

If you wanted to do it in two layers of lighter glass, say 400 GSM, you could peel ply between layers, which would virtually eliminate sanding.

[GILow]

Originally Posted by 44'cruisingcat

If you wanted to do it in two layers of lighter glass, say 400 GSM, you could peel ply between layers, which would virtually eliminate sanding.

Interesting, what advantage do you think this might provide? Stronger or easier to work with?