Deck Recoring....

Ed Schenck · Oct 18, 2009

Jerry, what is "complete deck recore"? Do you mean side decks and bow area? Or are you including the cabin top and sides? Wow, either way a huge undertaking. I did not look at your link, maybe it is the one that shows an entire side deck with the top f/g layer removed exposing the core. That project exists on here somewhere.

From my reading I think end-grain balsa remains a favorite coring. It seems like one of the synthetics would make more sense and I forget why they did not.

My advice would be to cut the top out of a suspect area of a manageable size. See what is there and how hard it is to get it up. Make your decisions about product and effort after that. I plan to do the exact same thing around my chainplates.

Ed Schenck · Oct 19, 2009

When I bought my '79 H37C in 1998 it sat right next to an '80 model. The '80 was a better equipped boat with the QM30 instead of 20 and nice canvas. The surveyor found the deck to be very wet. The marina quoted $6000. to make it right. Someone else bought that boat and sailed away. A few years later I heard that he sailed that boat all over the Great Lakes without incident. Makes you wonder.

JKeyes · Oct 19, 2009

Ed, Your story makes absolute sense to me. On survey of Hunter 34 the boat

I was intending to buy the surveyor informed me that the deck was wet on the starboard side. I was scared to go ahead at first and quite honestly coming to this web site fed the fears

but i talked with the surveyor who told me its very common and something you can expect to find. I got a quote on the repair and made sure the boat price was still reasonably priced with the repair costs included compared to other similar boats.

Unfortunately the owner wouldnt go down in price, that would have been sweet!, but then again the boat was already reasonably priced so I went ahead with the purchase.

I'm quite happy with the boat and one of these days may actually have it repaired! still not spongy.

name and address withheld to protect the owner from the stigma of having a wet core!

rardiH36 · Oct 19, 2009

Plywood Core or Balsa -- Makes a Difference

As Ed suggests, it would be a good idea first look at a small section. In particular, check if the core material is plywood, and not balsa. I mention because when I went to remove the top skin of my cockpit sole (the sole was spongy), I found that the core material of my 1980 Cherubini H36 was inlayed marine grade plywood of 4-6" squares. The water ingress in my sole had caused the plywood layers to delaminate, but the wood itself was still hard, not at all rotten, and still VERY FIRMLY adhered as new to both the top and bottom fiberglass skins. It was a devil to separate the skins from the wood requiring a couple of hours with a wood chisel, followed by a power sander. Area was only about 2' x 3'. Doing the same on larger sections of deck would really be a very extensive undertaking I would expect. In retrospect, because the core was not actually rotted, instead of removing the skin to replace the core, I would have bored holes or cut channels in the sole, let the core dry and then would have saturated with thinned epoxy to fill in the gaps and re-adhere the plywood layers.

I also believe that the deck core might also be plywood on these boats. When I bought my boat, the gelcoat on the sides of my cabin top had weathered down in spots to the underlying FRP. With sanding and then repainting with two part polyurethane, I now can see on the surface imprints of the squares (as in the cockpit sole) of core material that the fiberglass conformed to. Also, I seem to remember (but not 100% sure) that when I pulled up the shroud plates on the deck to pack with new caulk, that the core wood was in layers like plywood. Also it was definitely very hard ... not like balsa.

If the entire deck is plywood cored, it might account for the stories of these boats still going strong even after delamination and moisture was detected in the cores.

Don Casey's book, "Sailboat Hull & Deck Repair" has lots of info about repair methods.

rardi

rardiH36 · Oct 19, 2009

Another Bit of Evidence to Suspect Plywood

After pushing the button my previous post a few minutes ago, it occured to me of one other example of why to check for plywood. A PO of my boat cut the anchor locker hatch/door on the deck to make room for an anchor windlass. The core material is plywood.

regards
rardi

Seattle Scott · Oct 19, 2009

When I drilled though the deck ( on an '84) to move the wate discharge fitting, the core was plywood forward of the chain plates

Maine Sail · Oct 20, 2009

dvideohd said:
The two main candidates for recoring would be Corecell and End Grain Balsa... I know that the Balsa will bend "ok"... not so sure of the Corecell..

I there are large sections that have completely "mushed out" - then it might be EASIER to work on than just doing sectional work.. More time, but easier to do... if you see what I mean...

To summarize suggestions....

a - check a small piece first - perhaps near the chain plates....
b - see if the plywood is completely mushed out or delamin'd...

The plan would be to use large sheets - or as large as possible - to cover the deck.. two layers of 8oz fiberglass under Core - two layers of 8oz on top of core.. Epoxy for the adhesive.. Built up spots with Fiberglass for deck hardware and stanchion areas...
http://picasaweb.google.com/dvideohd/Mac26D04#5394556992446403506

Jerry,

#1) Do you own a moisture meter and have you sounded the deck? To many folks take the word of their surveyor on "wet decks" and as we know many surveyors are not even as competent as the checks we write to them.

#2) The lamination schedule should really not be tampered with. Unless you remove and ruin lots of inner skin, when pulling the plywood, I would not add any more to the inner skin than is already there. I would match your outer skin lamination to what the factory laid in and bond the new skin to the old deck edges with a 10:1 taper. The new balsa can be laid in to thickened epoxy on the inner skin. End grain balsa would be my choice..

#3) I would not re-lam using "large" pieces. I would rather use small sections with "dams" or breaks between the balsa of about 3/8" that can be filled with thickened epoxy. This limits any future water ingress to small sections.

#4) For checking laminate condition do some test drills from inside rather than out side. This way if you don't need to re core you won't have holes to fill. If you have a fiberglass liner then this becomes a more difficult choice.

Very often people do major re-cores on decks that are still structurally sound despite being damp. Stopping the water ingress on a damp deck can often yield many more years of use before major rot related surgery is required.

30% Moisture Reading Wet Balsa (this is NOT a pegged meter just 30%)

More 30% wet balsa in the early stages of rotting:

The Meter Reading:

A pegged meter, where the core would be even wetter than above:

Bone Dry Balsa (actual meter reading of 6%):

Maine Sail · Oct 20, 2009

dvideohd said:
I was going to try and use the old fiberglass deck pieces - and it's just possible to miss sports where there might be a water leakage point - even though I am trying to avoid that... places where there are some cracks or crazing that might let water through - but not be so large as to be visible. 8 oz fiberglass - two layers - at 45 degree angles - should not be be very thick - so should not impact the use of the old deck material.

Well... I wanted to learn from working on this boat... I really should know better than than to ask for something and then get it... :>

--jerry

Jerry,

From experience I would advise not re-using the original deck pieces. They will be tough to get up and will usually require cutting into small pieces. To someone who's never done this re-using deck skins seems like the easiest approach, but I can assure you that it's more work than just re-laminating it with new glass once the balsa is in. Laminating the new glass over the balsa takes no time at all. The time is in the removal, cleaning and re-installation of the balsa. Wetting out the new glass is a short job in comparison to the rest of it.

I was just helping a friend this weekend who thought exactly as you did. About 15 minutes into it he realized why I had suggested re-laminating it from scratch.

Johnb · Oct 20, 2009

How much of the deck is not solid GRP

Can anyone enlighten me as to how much of the deck is not solid GRP?

John Brecher

Seattle Scott · Oct 20, 2009

Johnb said:
Can anyone enlighten me as to how much of the deck is not solid GRP?

John Brecher

Probably everthing aft of the anchor locker.

Ed Schenck · Oct 20, 2009

As far as I know John there is almost no solid glass on our H37Cs. There is some that is really thick like around the anchor locker. And there is nothing under the coamings, they are thick but hollow. We have the raised areas at the mast, forward traveler, and hatches. But there is coring under those areas. I know the bridgedeck where my main traveler is located is solid. Not sure about the decking outside the coaming, probably solid.

sandpiper10471 · Oct 20, 2009

I have re-cored decks both ways - re-using the top skin and all new glass. I know that on my H37C the side decks from the water fills aft are cored with squares of ply. Same with the sides of the coach roof. When saturated, this ply swells to about 3/4 in. and you can see the outlines of it in the top skin. Haven't tackled the rest of it yet but I should know part way through next spring. However, I suspect most is balsa.

I have found the best tool for cutting out the top skin to be a 4" diamond blade on an angle grinder. Wear leather gloves , dust mask, safety glasses and tape your sleeves to your wrists to avoid major itch.

The old core can be a brute to remove. Other times it just falls out. Big chisels, prybars, slimjims etc. are useful. Some advise mounting the new core in a layer of chopped mat and polyester. I prefer a mix of epoxy or vinylester and cabosil. Make sure you wet out both the base skin and the contact side of the core with resin first and let it almost cure, otherwise the material soaks up all the liquid and there is not much left for the bond. If re-using the top skins then the joints must be bevelled 14:1 then faired with cloth. For the new top skins I prefer polyester. It is cheaper and plenty strong enough. Again, wet out the core. Never put poly over epoxy! It might not cure. And never use epoxy with chopped mat. They are not compatible. I have to agree with Mainesail that it is often faster (with less fairing) to do a whole new skin. And of course you remembered to put something non-absorbant (thickened epoxy, starboard etc.) in fastener/fitting areas before doing the top skin? And again, with a new skin, the area adjoining must be bevelled 14:1. A long straight board with 20 grit paper glued to it will help you with fairing. I also use a 9" 40 grit disk on a hard backing plate mounted to my large sander/polisher. You could probably also use a belt sander.

For cloth material I prefer to use 1808 stitch mat. However, for thicker laminations the job will go faster with 2oz. chopped mat alternated with 24 oz roving. But it will use more resin and not be as strong.

My coachroof side I did last spring as the core was soaked and the portlights leaked horrendously. I pulled out the ply coring and replaced it with balsa. The job was done from the inside.

So that is a very quick primer. Good luck and keep us posted!

sandpiper10471 · Oct 21, 2009

This project is labour intensive. re-using the top skins and polyester can help save costs. Sounds like you already have a pretty good inventory of tools and some experience. If you can drywall, you can put a good finish on glass repairs. Vacuum bagging can also help you do a bang up job.

Deck re-coring is not a tough job. Just dirty and time consuming. Balsa always wins when comparing costs, compressive strengths, ease of use etc. Anywhere your hull has squares of ply I would consider laminations of thin ply sheets (more strength and can take a bend) or balsa. Use ply in the stress areas or places of high torsion such as the transom. When I do mine I will use ply around the mast, the transom coring, cockpit sole. Under winches, pedastel base and traveler I will use starboard.

Mathurin · Oct 23, 2009

Here a few picture of the process, i completly redit the cabin top, sidewalks and cockpit floor last winter on my 81 hunter cutter 37. I'll post picture first (sorry they are not in order...), then if I find the time I'll give some advice ont the material/tools needed. Hope this helps... (more pics on page 2)
You can always contact me if you have anyquestion at:
mathurin2(removethispart)@hotmail.com

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