rot-proofing a marine ply cockpit....

[yourmomm]

hi-having put on hold my (post-yacht-fire /forums/images/graemlins/frown.gif....) renovation of my once-beautiful curtis and pape ketch to repair the rot i found in my gunwhales (thanks for all your advice TG), i have now found that the lifting teak deck in my cockpit hid a completely rotten substructure...ouch. joys of wooden owndership i guess, but i think ive got it in time, although am obviously am a little concerned about other areas of deck where fresh water accumulates and the sikaflex caulk is apparently compromised....

so i ripped out the 10mm teak deak without damaging it (so i can re-lay it), got rid of all the rotten panels (all of them were just mush) and softwood frame (?!!) of the cockpit, i have put-in a hardwood frame and am about to re-panel. i am using good quality 12mm marine ply which i intend to sheath completely in epoxy before laying.

i think the previous problem was poor drainage on the cockpit seats, where fresh rainwater used to accumulate, so when the sikaflex started to age, the freshwater just soaked the (unsheathed) ply underneath the deck. i obviously intend to do something about this drainage problem (though what im not yet sure....) but my question is this: in addition to the epoxy sheathing, is it worth also laying a thin layer of rubber underneath the teak to the flat sections of the cockpit, much like they do with flat roofs? it could provide added protection? many thanks for opinion or other advice in weatherproofing this vulnerable area...

 

[Seagreen]

I'd soak it in Intertox or cuprinol preserver prior to the first layer of paint, and let it dry.

BTW I wouldn't sheath anything in epoxy. In thin layers (unless you are building it like a tank) the epoxy will crack, and let water in to start the rotting process hidden beneath the epoxy. You can always scrape the paint back and re-preserve and paint. You can't do this with epoxy.

 

[pcatterall]

If the ply is properly sheaved with epoxy another layer of material is no help. Do you plan to bed the teak to the epoxied ply with epoxy. Clearly fixing with screws into the ply provides a possible path for water into the ply again.

 

[oldsaltoz]

G'day Yourmomm,

Some food for thought:

Rot proofing.
Any ply to be used in a wet environment should be treated to protect it from rot; this is best done after it has been cut to the required shape to ensure the exposed end grain is well treated. This applies to new material or recycled material and should be completed before any other treatment such as painting or epoxy coating.

Epoxy Coating.
Once the timber / ply has been rot proofed it should be allowed to dry out completely before applying any protective coating.

when Epoxy coating ply it is most important that all edges are well protected, you can mix small batches of epoxy resin and then add 30% by volume of Methylated Spirits to the mix; this will thin the resin and improve penetration.

Always start on the edges as they will need several coats because the exposed end grain will suck up the resin at a much higher rate.

When it stops disappearing it has reached saturation point.

Hope this helps.

Avagoodweekend......

 

[Tranona]

First thing to do is make sure water can't stand anywhere. Various solutions including angling the locker lids so they drain - is it a self draining cockpit?. Or building guttering around the framing, but again the water has to have somewhere to go. If the cockpit is non self draining then keeping it covered when not in use is the answer. I have an open drained cockpit, but use a fitted cockpit cover and the timber framing, mostly pine, and teak faced locker lids are fine after many years!

Don't have a problem with eopxy on the ply, but the problem is end grain which is difficult to seal and probably best capped. When I did my locker lids I used 2.6mm teak veneer strips bedded in epoxy with pigmented epoxy filler for the seams. Much better and lighter than using thick teak which moves at a different rate to the substrate ply.

Whatever you do, do not screw and plug. If you use Sikaflex as an adhesive do it under pressure such as clamping or concrete blocks. That way, no water can get at the substrate from above. Note that you have stripped the old teak. If it was screwed down you could still re-use it with adhesive and plug the holes, but still probably better to go the veneer route.

Hope this helps

 

[yourmomm]

err-NO screwing and plugging?! this doesnt bode well for the rest of my deck then, which has been fully screwed and plugged for the past 20 years....i have been concerned about this method of fastening the deck before now, yet there dont seem to be any leaks anywhere else in the yacht (unlike under the cockpit, where water would stream in...)-is this method of fixing really that bad if the screws are plugged well and sealed properly? cheers for all the good advice

 

[Sixpence]

My old Debutante has a plywood deck, screwed and plugged, no problems. The area I did have problems with were where the stanchions reached the deck and were screwed down. They were sealed around the outside but water got in through cable holes in the frame and was held in the bottom of the stanchions till it found the screw holes. It then went straight into the wood and rotted from the inside.
Agree with Seagreen though. Don't epoxy. It's just asking for trouble

 

[ccscott49]

I only seal the edges of ply with epoxy, the rest is rot proofed, primed and painted, Like Seagreen dont like epoxy sheathing, it cracks. Bed the teak planks in sikaflex, ensuring no gaps.
I did however epoxy all over my teak and holly floorboards, before varnishing. But there again, they dont get too wet!!

 

[Tranona]

If you have a "conventional" swept teak deck straight onto beams, ie no ply subdeck then you have no alternative to screws and plugs. Teak screwed to a sub deck of ply is usually OK if the ply is well sealed and the caulking is kept in good condition. However, there are so many potential places for water to get in that they are always vulnerable to rot. Teak decks wear unevenly and plugs can wear at different rates, so the temptation is to sand level and eventually the plugs are so thin they pop out.

This is more obvious on teak decks laid in this way on GRP decks, Often the teak is thinner to try and keep weight down, but the real villain is differential expansion that breaks the bond of the caulking, so letting fresh water in. This is a regular topic on the forum with the consensus that re-caulking and plugging is common after 10 years at £8-10k for a 40 footer and complete re-decking after 15-20 years at £25-30k!

It seem illogical to me that boats are built with an impermeable deck either sheathed ply or GRP and then drilled with hundreds of holes! The same applies to fittings where many are in fixed places and can be fastened into threaded plates boded into the deck, or on a ply deck set in epoxy plugs.

Screwing teak onto GRP decks has gone out of fashion and now many are thinner at 4-5mm, made up in sheets and bonded to the deck. This solves the problem of holes in the deck and the thinner veneers are more stable laterally. There may, of course be long term issues that we don't know about yet, but the cockpit sole and seats laid in this way on my Bavaria in the Med are in good condition after 7 years of hard use.

Cockpit locker lids are, of course less vulnerable than decks, particularly as they are usually laid straight rather than swept. However they need to be ply for stability, so why put 10mm of heavy teak on top? when the same effect (looks, non-slip and wear) can be achieved with a light veneer.

I think this is one area where "traditional" is not always best and newer materials and techniques result in a better job.