How to seal a wooden deck ?

[BartW]

Hello, first post on here,
I’m a regular on the mobo subforum

When Our old (1991) Canados 70 mobo was build, the Canados yard (Italy) was in transitions from wood to GRP build boats.
Our’s has a GRP hull but deck, gunwale and superstructure are wood.

The deck consists of plywood on a wooden framing, with a top layer of teak (original thickness was 12mm)
But after 25y and many times sanding, the thickness is <5mm in some area’s.
5 Years ago we have recaulked the teak , and first cut out all the caulking grooves down to the plywood surface

But now more and more water leaks to the lower level are appearing (and we try to fix each time)
So it is time to renew the teak,
Next winder we want to do this work, but start now with the planning and preparation.

So far this is our plan:
First take off the old teak
Then repair potential rotten panels of plywood, and or frames,
Looking from the lower level (cabins, engine room , utility room... ) to the underside of the deck, condition is mostly OK,
but there are a few spot where some repair work is needed.

When we have a complete refurbished plywood floor (and potentially a few new frames),
I was thinking to place one or more layers of glass mat and epoxy on top, to achieve a sealed surface.
The mats can be feathered or glued upwards against the superstructure (wood) and the gunwale (GRP)
Then the new teak goes on top of this sealing.

Some people advice against this layer of glass mat / epoxy,
Because of potential moisture issues’s in the underlying plywood panels from condensation.
Another point of consideration is potential crack’s in the matting,
The hull with wooden deck can have some flexing when this heavy boat is in rough see,
Won’t this flexing cause crack’s in the glass/epoxy layer ?

What does the forum think
Is the proposed system ok?
What is the best way to seal these decks ?
thanks for opinions

cheers.

 

[Rum Run]

I have a similar but smaller job at the moment, with a 31' sailing boat having a GRP hull and Cascover sheathed plywood deck. The intention being to re-sheath with woven glass and epoxy once all the fittings, toerail and rubbing strake are off.
As Cascover is impervious to moisture, I assume that epoxy sheathing will not cause more condensation problems than before. Perhaps you may need to be more assiduous regarding ventilation, especially if there are many closed spaces like lockers which go up to the deck head, but I don't think plywood is a very breathable material anyway I suspect your plan will be fine.
The killer might be if you replace the teak by screwing it down through the new epoxy + glass layer, as this will give a pathway for rainwater into the plywood. If you vacuum bag the teak down while glue goes off it will remain waterproof, but it limits the shapes of plank you can put down. Maybe Flexiteek (sp?) may be better. Less maintainance and lighter anyway.

I'm not sure about the effect of flexing with your boat as 70' is out of my experience, but maybe the way forward is to be quite generous with the layup? I think glass cloth rather than matting would be better, perhaps adding woven tape over the joints if not using several layers of cloth anyway.
I look forward to seeing what others suggest

 

[Tranona]

The first part of your treatment sounds OK, although I suspect you will need to replace much of the ply sub deck, particularly if your teak is screwed down. Although the ply may appear sound from underneath, it rots inside and it is pointless using epoxy on anything other than sound dry ply. You may also find it is laminated in 2 layers if there is any curvature in it - probably 2*9mm. You won't know the real condition until you get the teak off.

Sheathing in epoxy glass cloth and then fairing is pretty standard practice and will make the substrate both rigid and watertight. If you are going to spend your kid's inheritance on a teak overlay then just glue it down. Does not need to be 12mm, 9mm will be fine. 12mm is more common with screwed decks to give extra depth for the screws and room to reset them lower when the plugs and deck surface wear down. Wear on glued decks tends to be less as they are flat smooth surfaces and wear starts often around the plugs leading to hills and valleys.

An alternative is to make the ply deck thicker, say 25mm total and then lay a glass epoxy surface, finishing with a non slip surface like Kiwigrip on the walkways. Aesthetically different, but a fraction of the cost and far more durable!

 

[DoubleEnder]

The current system has lasted 25 years so it would seem sensible to repeat it. Basically I think repaired ply, glass sheathing, teak cover is fine. If at all possible glue the teak down rather than screwing it down to avoid water getting in to the ply. But this won't solve the problem 100%, as there are places where fittings will be attached .....water will get in.

I fear Tranona may be right and the existing ply will need extensive work. I'd budget and plan to replace all of it. If that means you have to live without the teak then that's a trade I would do.

About 10 years ago I had a 34 foot all wood sailing boat rebuilt. The boat builder and I had several long and energetic discussions about how to make the new deck. I wanted a ply sub deck, he was against it. Of course we decided his way was best... his argument is that water WILL reach the ply, and that when it does it will seep horizontally to places where it can do expensive hidden damage - such as the complicated part where covering board, sheer clamp and beam shelf interact with the topsides. But it won't become apparent until the damage is expensive and difficult to fix.

If, however, you simply have the teak decking screwed directly to the deck beams then any water ingress will be immediately evident and can be repaired quickly and cheaply. That's what we did and so far so good.

You have the blessing of a GRP hull so this is not a worry for you.
Some of the synthetic teak looks pretty good and I think you can get panels made up so that might be worth checking. But I don't think it is cheaper to buy. May be cheaper to maintain perhaps.

Good luck.

Graham

 

[BartW]

Thanks for the comments and advice
I’m glad that here are 3 opinions confirming what we have in mind,

Our plan was indeed not to screw but to glue the new teak on the GRP layer, just like on any new GRP boat.
and hold it down with weights (or vacuum bagging if we are able to organize that)

good advice to replace the old plywood from the deck
now when the deck is open , we should do this thorrowly,
deck is slightly curved so 2 x 9mm marine ply is the way to go.

Probably I’m on the right subforum to say that I prefer real teak,
I think a boat of this vintage only looks OK with real teak,
And for me, walking on it, and the feeling of real teak is part of the enjoyment of a boat.
Oh and don’t worry about the kids, even without their heritage, they are starting their adult lives with a lot more of everything than I did at that time 

all agreed about ventilation below the deck,
actually our complete superstructure has quite a few layers of paint,
the plywood under this paint is impeccable almost everywhere,
BUT
A known problem on Canados Yachts of this vintage are the gunwales, plywood on both sides,
And “almost” complete water sealed, so no ventilation, but condensation inside.
Result: the exterior paint is bubling in some area’s and the wood is rotting.
Replacing these gunwales, and allow them to ventilate, is another part of the work for next winter

Cheers Bart

 

[DoubleEnder]

The boat sounds great. Send us some photos!

 

[BartW]

The boat sounds great. Send us some photos!

in this thread are quite a number of photos, from many different rebuild jobs,

http://www.ybw.com/forums/showthread.php?295561-Blue-Angel-(Canados-70s)-Rebuild-thread