Drying out a cored deck?

[Peters Wet]

My boat is a Catalina 30 1978 and the previous owners neglected to rebed the deck penetrations, I dont have soft spots(at least none that respond to my 250 lb footsteps and Im in the process of rebedding everything. My question is if there is a way to dry out the deck? Should I bother? Any opinions or experiences would be appreciated

[Rotten Ricky]

It is very important to prevent delamination of the deck by preventing ingress or removing any moisture if possible - remember that polyester resin does not adhere well to wood - epoxy should be used. Your deck is probably half-inch sheathing if it is the same as my former 1975 Catalina 30. Unless you are able to leave the boat on the baking Nova Scotia sunshine in the summer for a while, you might need to rent or buy a dehumidifier to suck the moisture out of your deck. Either way, all fasteners should be removed, of course. It will take time - it took a long time to seep in there.


All fasteners on a deck should be through or into a solid column of thickened and fortified epoxy - just screwing them to the outer glass layer is a poor substitute, and sooner or later, water will penetrate. Through-bolting is preferred to screws. Depending on how big the fastener is, the location should be drilled out over-size right through to the interior of the boat, then if possible remove some more of the core all around the hole as well. After drying out the deck, apply some duct tape across the inside face and fill the hole with thickened and fortified epoxy. When it is set, clean up irregularities on the inner and outer surfaces, paint it if needed, and drill the nominal diameter hole and install your fastener. For my 1/4" bolts and machine screws, I drilled the hole to 1/2", so there was a 1/8" solid column all around the bolt.


This might seem a scary thing to do, and there is some time and expense involved but it will give you bullet-proof attachment of your hardware, because the column of solid epoxy is locked between the f/g layers and will not compress under loading compared to your present situation where the plywood centre will crush.


I would recommend that you use butyl tape as a sealant which is obtainable and cheaper from RV stores - a big roll is only about $10. It is so much cheaper and easier to use than the advertised sealants. Mine were in use for 15 years of sometimes strenuous use and none of them ever leaked - even the windows.


You do not ever want to be faced with a delaminated deck. Incidentally, if you "sound" your deck by tapping it with the plastic handle of a heavy-ish screwdriver you will quickly find out if delamination has occurred. The sound will change to a higher, musical, bouncy "plunk" compared to the more solid "thud" ones. The handle will bounce higher as well if the deck is delaminated. Look especially closely just down a slope from any fastener. Also look for any surface crazing (cracking) especially around any stressed hardware like stanchions, etc., because they indicate a cracking of the f/g underneath. Good luck.

[ccgarnaal]

I had a moist core underneath the teak on my 1963 Trintella.
After removing the teak I drilled holes ever few cm to determine how wet my core was. (Balsa core without cells)
Most of it was wet but only a small part started to rot.

I sawed out and replaced the rotten part. The rest I let dry.
I removed 2/3 oh thickness from the top fiberglass layer of the deck using a vertical rotating electric plane. Than I drilled 15mm holes trough the fiberglass everywhere it was wet (usually around the screw holes of the teak deck that leaked. (The deck looked like a cheese grater)

After the core was dry (confirm using borrowed moist meter from boat yard)
I soaked the deck in liquid epoxy which was easily absorbed by the balsa wood.
And put new fiberglass over it. Then I put the teak deck back.

And I agree with Rotten ricky as for the thru deck bolts. Don't use screw bolt everything and make a epoxy tube for each bolt.

Don't cover the hole at the bottom with duct tape. The liquid epoxy will dissolve the tape and you will have epoxy run everywhere inside. Close the holes with epoxy paste from inside and the fill then with liquid epoxy from above. The liquid epoxy will nicely soak in to the core so you have to refill after 10-30 min but it will work nice.

As for the butaseal tape, it's a choice I personally prefer simson construct or sikaflex kit. But most boatyards use butaseal tape because of its ease of appliance.

3th picture is a nice photo of the core sawed open:
From left to right you see piece of hardwood in the core the deck was screwed on. Green rotten balsa you could remove with a spoon soft as yogurth. Dark brown wet but not rotten balsa wood. And right dry light coloured balsa wood.

[Cheechako]

You can drill small holes from inside the boat to determine extent of wet core.
Drill thru into the core only,
pull the drill out and remove the balsa that is in the spiral grooves of the bit,
squeeze the balsa between your thumb and finger,
water will come out if wet.

[Rotten Ricky]

Regarding duct tape and others, it could be that there are slight differences in the chemical composition of the adhesives used, depending on what part of the world you are in. I have never had epoxy dissolve and leak when I have taped the inner end of the hole into which fortified epoxy is to be poured. However, polyester resin will often dissolve some adhesives, plastic foams, etc.

Always use epoxy for this kind of work. Epoxy will bond to almost any other material, including polyester, but polyester resin will not bond well to epoxy.

Some epoxy is especially formulated to set up in damp or wet conditions. It is usually a very thin resin that will soak into damp wood or of poor integrity.

It is possible to drill only through the outer layer of f/g and the core, and not through to the interior. This reduces any surface repairs inside the cabin, but it does not allow such good air flow to help in drying out the core. If drying out is not needed, I would go that route and use a flat-bottomed router bit or similar to remove the core from the middle while not puncturing the inner f/g laminate.

Regarding application of any sealant, it is best to apply them and assemble everything in place but do not give a final tightening of the assembly for a day or two or until the set up into a solid rubbery gasket. Then with the last little bit of tightening, it compresses the "gasket" and so you are not relying only on the adhesive properties of the sealant to prevent water ingress. This is especially true of work done below the waterline. I would not use butyl tape in a location below the waterline or if the fitting has a single shaft like a bolt around which the fitting can rotate under strain.

Looks like you have restored a beautiful classic sailboat. Well done!

RR.