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-   -   Wet plywood deck core - how to dry? (http://www.sailnet.com/forums/gear-maintenance/62424-wet-plywood-deck-core-how-dry.html)

laHolland 02-28-2010 05:14 PM

Wet plywood deck core - how to dry?
 
We noticed that there was some coffee-like liquid oozing from a seam on our Cal 27's cabin ceiling. So we knew we had a soggy deck, though it doesn't feel spongy when walking on. The boat cabin isn't lined, and there isn't any paneling or furniture in the way, so it is easy to access the deck from the interior. We cut out a small section with a dremel tool, without going through to the top. The construction of the deck is, from the top to bottom, gel coat, fiberglass layers, plywood, fiberglass layers. The small section we removed revealed that the plywood was damp but does not appear to be rotten or mushy. The plywood was still attached firmly to itself and both layers of fiberglass. So my problem is -- how to effectively dry out this plywood? The area that needs to be dried is large - I think the moisture wicked along the wood grain, from a leaking chainplate nearly back to the companionway. I expected the plywood to be rotten, but it is quite firm and we really had to pry/chisel it off, though it is clearly damp.

So, I am thinking we can pry/peel away the inside fiberglass layer, and attempt to dry the plywood from underneath using a heater, but I don't know if this will work, as the water vapor cannot escape upwards without putting holes in the deck surface (which I'd rather not do).

Anyone had any experience with this, or any ideas?

sailingdog 02-28-2010 05:46 PM

I don't think you're going to really effectively dry out that plywood in any reasonable period of time. It has probably taken a long time to get this wet, and would take a really long time to dry, especially with only one side exposed. IMHO, you'd be better off re-coring the cabintop. Marine plywood is the worst of all core materials for cored laminates, as you can read about HERE.

If you do decide to recore the deck, it would be my recommendation to cut the top laminate layer away rather than try and do the work from the underside. Working from the top will make the repair go much faster and gravity will be working with you.

Working from underneath will require you to mask off the entire interior and will make it much more difficult to get a good layup without voids. Finally, any bulkheads are going to make getting the core repair more difficult to do.

Finally, I'd recommend using end-grain balsa or a ductile polyurethane foam like Divinylcell. While a rigid foam might be better, it would be harder to work with. For end-grain balsa, something like ContourKore, which is designed to allow the material to follow fairly complex curves, rather than solid sheets of it, would make laying up the new core much easier.

You should probably plan to make the areas beneath major hardware solid laminate, rather than cored laminate, and any smaller hardware that is mounted through the cored areas of the deck should have the fastener holes potted. To do this properly follow Maine Sail's excellent directions.

I'd also recommend you read my article on marine sealants prior to rebedding any deck hardware. One of the most versatile and effective sealants is Butyl Rubber Tape, which you can get at many glass repair shops. Not only is it very useful for bedding all kinds of deck hardware, it is also very inexpensive compared to other marine sealants. However, I would not recommend it for below-waterline use.


Quote:

Originally Posted by laHolland (Post 575165)
We noticed that there was some coffee-like liquid oozing from a seam on our Cal 27's cabin ceiling. So we knew we had a soggy deck, though it doesn't feel spongy when walking on. The boat cabin isn't lined, and there isn't any paneling or furniture in the way, so it is easy to access the deck from the interior. We cut out a small section with a dremel tool, without going through to the top. The construction of the deck is, from the top to bottom, gel coat, fiberglass layers, plywood, fiberglass layers. The small section we removed revealed that the plywood was damp but does not appear to be rotten or mushy. The plywood was still attached firmly to itself and both layers of fiberglass. So my problem is -- how to effectively dry out this plywood? The area that needs to be dried is large - I think the moisture wicked along the wood grain, from a leaking chainplate nearly back to the companionway. I expected the plywood to be rotten, but it is quite firm and we really had to pry/chisel it off, though it is clearly damp.

So, I am thinking we can pry/peel away the inside fiberglass layer, and attempt to dry the plywood from underneath using a heater, but I don't know if this will work, as the water vapor cannot escape upwards without putting holes in the deck surface (which I'd rather not do).

Anyone had any experience with this, or any ideas?


laHolland 02-28-2010 06:26 PM

Thank you for your insights. We will only be repairing the port side of the boat - the other side is dry and solid. Would it be bad to replace one side of the boat with a different core material than the other half?

Also, our cabin interior is currently undergoing a rehaul (read, it's a complete mess), and we were planning on redoing the interior ceiling anyway (peeling paint, stains, sharp, poorly laid fiberglass surface, very yucky), so it's much more appealing doing the work from the inside, especially since one of the few unblemished parts of our boat is the deck. Also, there's the weather issue. In your opinion, is it completely impossible to do a halfway decent job from the under side? I say "decent" - I don't expect perfection.

sailingdog 02-28-2010 06:49 PM

It isn't ideal to have the two halves of the boat cored with different materials. However, it isn't a complete deal breaker IMHO. However, doing the work from the underside is going to take a lot longer and it is a lot harder to get it right. If you brace the layers properly, you can probably do a decent job of it. Using vacuum bagging would help, but that may be more complex than you want to get into.

One person I know who did this on two different boats said that doing it from the underside took about four-to-five times as long and that isn't counting the clean up, which was a lot more laborious as well. The repairs were about the same size IIRC.

If you do decide to do this, I would highly recommend using epoxy from Progressive Epo_xy Polymers and Resins in NH and getting your fiberglass from www.fiberglasssite.com. Remove everything from the cabin that you can and tape a heavy plastic tarp over the interior.

I also recommend using a full-face respirator mask with vapor and particulate filters rather than goggles and a half mask. DO NOT USE THE DISPOSABLE MASKS—they are worthless. The full-face mask respirator will last a long time if you care for it properly and is far more comfortable than the half-mask and goggles.

NICHOLSON58 02-28-2010 06:55 PM

There is another option for core material I am using to rebuild my rudder. The original with three SS ribs and foam core with glass and Kevlar skin was totally waterloged. I built up inner structures and then filled with syntactic foam. The mix I used was 3 gallons of low viscocity Epoxy resin and 7 gallons of 3-M micro-balloons. The bleded gooy mass is like warm Kraft Marshmellow creme. Cured, it is supposed to have a compressive strength of 3000 psi. The resin is no-blush 635 from US Composites. (they also sell the balloons and cloth) The "foam" can be easily sanded and shaped. The finished skin will be graphite & vacuum bagged. My intent is to have a truely water-proof structure.

You might consider using this system to form your core in situ if you can leave the insided glass layer in place. (make gravity your friend). I have also found that you can form the stuff if you put down the foam and apply a release film. If need be, you can also press the film to hold it in place by using cardboard forms and props. You should get excellent bonding to this material as you build up the top layers. I suggest you try a few resin & balloon ratios to decide what will work best for you.

davidpm 02-28-2010 08:56 PM

Quote:

Originally Posted by sailingdog (Post 575236)
I also recommend using a full-face respirator mask with vapor and particulate filters rather than goggles and a half mask. DO NOT USE THE DISPOSABLE MASKS—they are worthless. The full-face mask respirator will last a long time if you care for it properly and is far more comfortable than the half-mask and goggles.

SD
Do you have a link to a mask you have in mind? Also do they work with paint products like AllGrip too?

davidpm 02-28-2010 09:05 PM

Quote:

Originally Posted by NICHOLSON58 (Post 575240)
I built up inner structures and then filled with syntactic foam. The mix I used was 3 gallons of low viscocity Epoxy resin and 7 gallons of 3-M micro-balloons. The bleded gooy mass is like warm Kraft Marshmellow creme. Cured, it is supposed to have a compressive strength of 3000 psi. The resin is no-blush 635 from US Composites. (they also sell the balloons and cloth) The "foam" can be easily sanded and shaped. The finished skin will be graphite & vacuum bagged. My intent is to have a truely water-proof structure.

Do you have a link or part number for your micro-balloons. I didn't see it on the site. Also where did you find the 3000 psi number

ROSA 03-01-2010 04:16 AM

If the area is not too too large and the plywood is still in good shape I would remove the interior skin and place a dehumidifier inside, seal up the cabin, and let it run for two weeks or so. They work better than a heater and you may find that the removal of the wood is not necessary at all, assuming that it is still well attached to the outer skin.

A friend was able to dry out the interior of his West sail 32 in this manner and found everything in good shape and ready for re-finish. It is certainly worth a try before you really know if a re-core is necessary. He also discovered in this process that he had termites, due to the wet wood. They, the termites, dried up like grains of rice and covered all flat surfaces.

laHolland 03-01-2010 08:54 AM

That's a good idea, Rosa. I think I will try that first, and then reevaluate.

sailingdog 03-01-2010 10:44 AM

The 3M series 6000 full face mask respirator is the one I use.

See HERE.

If you're talking about AwlGrip, the two-part paint, I would highly recommend not spraying the stuff. It has an isocyanate (cyanide) based component that can be lethal if inhaled.

Quote:

Originally Posted by davidpm (Post 575308)
SD
Do you have a link to a mask you have in mind? Also do they work with paint products like AllGrip too?



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