Wet ply in deck - how to dry

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mattonthesea

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For reasons that I am too embarrassed to explain I have a question around drying out a ply core around a hole in the foredeck. This used to be where the anchor chain went through. It is a sandwich type deck strengthener. About 25 mm thick with 12mm being the ply.

Anyway, today I was going to fill the hole with a loose ply plug and epoxy a la West Systems advice. However, when examining the ply around the hole it was soaked enough that it oozed water out when I applied pressure with a screwdriver. Now I was relatively sure that it was dry two days ago when I left the boat and it has rained for 12 hours since then. Now I am not so sure. It is drier on the side towards the front of the boat Up hill).

My thoughts so far:

at least it is not balsa wood!

how far does the damp spread?

will it dry on it's own? It's open to the sun for some several hours a day (but it was sealed in during April!!!)

For the moment I have sealed the hole both top and bottom with gaffer tape and put some rice in to absorb some moisture. Would it be better open to the elements? Is there a better way of drying?

Will I have to get hold of a dremmel type drill and excavate?

Can anyone give me some advice or point me to a good web/youtube site

Thanks
 
If the bottom side of the grp is accessible, you could drill a small hole (say 7 or 8mm), only as deep as the GRP layer, just to reach the ply inside.
I would drill it on the stern side of the hole (which goes "downhill", if I understand correctly), and at a distance of one inch or so from the existing hole.
If the ply inside would still be wet, I'd drill another hole on the same direction, at a distance of another inch, and so on till you will find a perfectly dry wood. Hopefully, you will not have to drill more than 2 or 3 holes.
At that point, on top of having a decent estimation of how far the damp spread, you also have some drains, that will help a faster core drying.
And will also allow you to monitor how the drying out progresses, possibly helped by some hot air.
Goes without saying that the upper side will have to stay protected from rain for as long as necessary to dry out the ply and complete the sealing.
 
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I think your going to struggle to dry that out if the moisture has got any further than a cm or so into the ply. It’s worth noting that ply is worse than balsa for moisture transfer as the laminations of the ply encourage the water to track along whereas end grain balsa resists transfer surprisingly well. Although I doubt it’s what you want to hear, your only real option is to start cutting back the grp skin until you find dry substrate then repair it.
 
Keith-i said:
ply is worse than balsa for moisture transfer as the laminations of the ply encourage the water to track along whereas end grain balsa resists transfer surprisingly well.
Click to expand...
Hang on, there's plywood and plywood. I'd have phenolic glueing Okoumé plywood rather than end grain balsa anytime.
Regardless, I agree that depending on the ply quality and how deeply the moisture penetrated, in the worst case it might be necessary to do what you envisage. BUT, as a first step, I would check the situation as I previously described anyway.
Should some holes reveal that the ply inside is extensively soaked, it will always be possible to bite the bullet, cut a section of the GRP skin and rebuild the sandwich. Just as a last resort, though.
 
If you can get power to your boat why not put a fan heater inside the anchor locker ? A few days should sort it 'check for soft spots by tapping the area with a screwdriver handle.
 
I have a glass over ply boat and am paranoid about water getting into the ply so i am always on the lookout...
I found a soft spot on the top edge of the "windows" cut in the nearly but not quite vertical cockpit coamings. i.e the underside edge if you see what i mean.
Last place i would have expected! I could only conclude that the water ran down the vertical face and hung in drips on the under side edge where it was quietly absorbed into the cut edge of the plywood. Probably an edge where its easy to miss with epoxy and paint as well cos you have to lie on your back in the cockpit to see it properly.
Perhaps you have the same kind of thing with water running down the deck and continually soaking the face of the cut on the high side where as the low side only experienced direct impact rain. If its good quality plywood, when you dry it out it will be hard and resist tools. If its gone bad then you will be able to dig it out as a crumbly mess.
If repairs are needed, don't be shy about going large! As a general rule, its often easier to cut out back to a deck beam or whatever and put in a larger piece than try and blend in a small patch.
Good luck
 
You could drill pin holes from the inside to poke a moisture meter in, but if it is just recent rainwater ingress from a raw edge it should not have penetrated 'that' far and should dry from that raw edge in a not unreasonable time.

If possible I'd repair the outside and leave the inside open for the Summer. Maybe screw a temporary plate (wood, aluminium or even plastic) over the hole if you cannot fix it without a backing.

It would be best to allow free circulation of air over the edge as it will dry quicker, but that would involve tenting and not using the boat, hence the patch.

I would choose a dehumidifier over a heater for drying, but only if the boat was on my drive and the cabin was easily sealed.

However, you may find that the ply has 'blown' if it was not of sufficient quality. If so, the most rational* solution is probably anti-panic sunglasses, then introduce some wicking resin after drying it.

*All this is assuming the boat is not worth six figures... In that case you may prefer to do it properly.
 
GRP hoatbuilders have a nasty habit of using pretty rubbish wood and/or ply where thety think it's never going to be seen - ie laminated in when they build the boat or covered later by better quality timber. I once had a boat with lots of solid teak everywhere, all bronze fittings, but deep under the cockpit sole was sawn wood that looked like recycled bits from an old softwood pallet.

Drilling holes in the underside to help drying is cosmetically better, but you then have a horrible "working overhead" relaminating job if you want to do this. Drying could be remarkably slow unless you expose a large area.
 
dialdan said:
If you can get power to your boat why not put a fan heater inside the anchor locker ? A few days should sort it 'check for soft spots by tapping the area with a screwdriver handle.
Click to expand...
Agree.
Drilling lots of holes seems a bit OTT at this stage.
 
I didn't suggest to drill "a lot" of holes, actually.
I guess that anywhere between just one at best and 3 or 4 at worst should be enough.

Btw, the OP said "around a hole in the foredeck" which "used to be where the anchor chain went through".
That's the reason why I guessed that the inside area of that part of the deck should be accessible from some hatch, remaining totally hidden from outside view. So, also re-sealing the holes once the problem is sorted shouldn't require any attention to aesthetics...

Anyhow, also assuming that the ply could dry out naturally or with some hot air blown around the existing hole, I would still prefer to understand to which the extent the moisture affected the plywood first, regardless of if and how quickly it will eventually dry out.
 
Paulg25 said:
Agree.
Drilling lots of holes seems a bit OTT at this stage.
Click to expand...

At this stage there is no need to drill a lot of holes, just a few to see how far the moisture has spread assuming under the ply is laminated I would just drill through the laminate and use a screwdriver or similar to see how soft the wood is.

So, say 1x4mm hole @ 25mm from the opening, if that is soft/wet drill one a further 25mm away and so on until, do the same at say quadrant points around the opening.

That way the op gets an idea of the extent of the problem and can formulate a solution.

I am assuming the ply has fibreglass laminate above and below. If dry @ 25mm around the hole dig any rot out with a bent nail in a drill. Allow the remaining wood to air for while and fill the gap with thickened epoxy.
 
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Just had a thought, to accelerate drying if you do drill some small holes, poke the end of a length of string into the hole to help wick water away.
(Think plastic jungle.)

Also could use a large forstner bit with a drilled plank as a drill steady to cut a series of drying holes while leaving the bulk of the deck structure intact.
 
I thought I posted this yesterday but ...

Thanks all.

Update:

I have dug around the hole with a chisel. The 'uphill', forward end of the hole appears to be just damp. The sides and aft end is soft and wet. I drilled two 5mm holes 25mm aft at an angle of 45 degrees off the line, one of which was oozed water when pressed with a braddle (?sp) and the other was firm. I couldn't go straight back because there is a bulkhead just behind the hole. I removed the head lining behind the bulkhead and was surprised to find that the ply fillet (is that the right term?) only extends to the bulkhead. The raised longitudinal line of the foredeck only contains the fillet in front of this bulkhead; aft of it it is cosmetic. I had to stop there as I was running out of exercise time. The boat is a cycle ride away.

It is obvious that the water has been seeping in for some time. However, the ply needs digging out with a chisel; it's not hand crumbly.

I have no access to power except for a small inverter. I cannot get to a power source until lockdown is eased. I do have a Dremel
 
Very similar to my present situation on my wooden Folkboat. There's a 'soft' area of deck at the place where one 1st puts a foot onboard coming from pontoon to boat, with a bit of movement in the deck surface. I took this to indicate that at the very least, the GRP sheathing had come away from the plywood.
Big brave step, I cut into the area with a dremel, and kept removing bits of totally sodden ply, until I reached a 'firm & dry' area. From underneath there was no indication of wetness at all. This was yesterday, and I've fought the urge to reseal it, and complete a full repair, deciding instead to leave it for a couple of months (we're not craning in this year!), to let it completely dry out. It's in a position where the sun and wind get to it, and won't get any worse.
The area that I cut out was about the area of a foot, and 'should' be easy enough to repair as it's accessible from above & below.
Good luck.
 
Update

I left the hole open to the sun for 25 hours and it has almost completely dried on the surface edges. I dug at it with a chisel and no signs of water retention. I then used a Dremel to explore deeper and, again, no signs of rot/damp. So I think I'm lucky.

I'll leave it to dry completely and then glass it in with a plug. I reckon that I can create a base layer under the deck and then build up a little way and let that go off. Then I can use some thin epoxy to run down and into the ply , possibly using a syringe and kwill, before plugging with ply and 'peanut butter'.
 
mattonthesea said:
Update

I left the hole open to the sun for 25 hours and it has almost completely dried on the surface edges. I dug at it with a chisel and no signs of water retention. I then used a Dremel to explore deeper and, again, no signs of rot/damp. So I think I'm lucky.

I'll leave it to dry completely and then glass it in with a plug. I reckon that I can create a base layer under the deck and then build up a little way and let that go off. Then I can use some thin epoxy to run down and into the ply , possibly using a syringe and kwill, before plugging with ply and 'peanut butter'.
Click to expand...
If you use West System, use their 209 extra slow hardener and heat the wood before applying the epoxy. the heat opens the wood cells, flashes off some of the gasses and reduces the viscosity of the epoxy. this will ensure that it will seep better into the wood. the extra slow hardener gives it more time to seep in before kicking off. DO NOT thin the epoxy. thinned epoxy loses its ability to bond to the structure.
 
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