Love-hate relationship with teak decks

I like the way teak looks, but hate what it does to the underlying structure. Granted this boat is 47 years old. I almost like it with no teak, just white paint.

Rain water sits under the teak and rots the plywood and supporting framing. I spent the last couple of weeks removing the teak boards and redoing all the framing and plywood with PT wood.
The wood surface I painted and sealed over the top with PL.
Still working on it, got one side done, other side almost done and starting on the rear now.

I have improved the strength over the OEM design, my new side inside cockpit support rails terminate at the transom supported on a shelf whereas before they terminate into the rear plywood curved support piece.

I had to replace the rim wood that fits inside of the planking. all the wood forward of the teak is fine being sealed under plywood decking.

This is an album
boat aft replace decking Fall 2017 https://1drv.ms/a/s!AqrOjz4_QIRDiTvnIMWu3ERZ3SK0

6 inches of built up wood layers on the left is the OEM design which is good.


The inside plywood support rail now terminates all the way aft as part of the transom framing
I made a triangular bracket to lock the inside plywood support rail to the rear plywood mahogany partially rotten support rail, sitting behind the teak. That piece has a double curve. Plan to cut out the curve shape from a larger 2x lumber, then split in half so it will bend into position.


Showing outer corner glued up


Plywood on before being sealed.
Plywood is pretty narrow all around this deck. Lots of solid wood on the edges. But it was all rotten.
I had replaced some of the wood back in 2001 with PT when I replaced the transom, and that has bee fine, such as the wood in front of the rear transom top plank. When I did that, I replaced all the supporting structure of the transom with arsenic CCA PT wood. And it's still perfect.

 

In spite of your efforts, the subdeck is going to rot again. The only way to install teak (veneer or laid) over plywood is to encapsulate the plywood (epoxy) then sheath it with a couple of layers of 6 ounce (200 gsm) as a minimum, then lay the teak. Simply put, you have to have a stable, water tight substrate before the teak goes down.

 

The ply is ground contact rated, so it will not rot.
I had replaced the other sides plywood and all the rim wood or (gunwale wood) back in 2006. But did not replace the mahogany inner support plywood rail at that time, so of course it is rotten.
Had to remove all the teak covering boards anyway since the plywood for the rear deck goes under the side deck. That side plywood is fine. I will post more pictures.

The OEM builder had used a layer of dark red rubbery soft caulking which glued the teak onto the plywood. Back in 1970 what was it? a polysulfide? It actually stuck well to the teak. Since most of the original ply was badly rotted, the teak has been able to be removed mostly intact.

Potential future rot issues are the top edges of the mahogany planking. Some of the teak boards screw into that top edge. In 2006 I replaced both sides top hull side planks, and they showed small surface rot which I scraped off and treated with oxalic acid. Plan to paint with zinsser primer then overcoat with PL. Screw holes can be a problem letting in water.
Also years ago, I had to go to larger screws that hold the SS deck railings. At the time I forced DAP Dynaflex acrylic caulk into the holes and coated the screws and that has held and not rotted. I am thinking do the same with the holes passing into these top mahogany boards.

I have been putting up with the slowly rotting substructure under the teak for many years.

 

Ground contact PT will rot, in spite of the label's suggestions. This stuff can tolerate occasional moisture contact, but let it pool and it rots, just not as fast as untreated stock. Also epoxy doesn't stick all that well to the new PT coatings they're using. The rubbery stuff was possibly a red lead based product, though maybe polysulfide, this is usually black or white, most commonly black. Moisture getting past the fasteners and collecting around them, between the teak and substrate is the primary reason things happen. Only epoxy bonded faster holes will prevent this and the substrate has to be fully encapsulated, preferably with a sheathing. Most insurance companies will not permit a claim, unless there's a minimum 12 ounce sheath over and properly prepped plywood subdeck, on any teak overlay.

 

Showing the PT wood I replaced in 2006, in fine shape, not degraded at all. Two white pieces are new wood.



I sanded the surface to clean up the dirt and such. I scraped the mahogany top planking edge to clean wood, treated with oxalic acid. Then smeared in some Titebond 3 glue.
I will paint, then fill with some PL those frame pockets, then paint again on top, or some such method.



Otherside sealed and painted with primer.
You can see the ends of this degraded mahogany plywood support for the back teak decking.
I found out this board curves in 3 directions, it humps up in the middle, has a concave curve, AND the bottom edge twists forward about 5*


I have created two angular triangular brackets from wood for the inside corners to support the inner plywood support rails. Basically 2 2x6 pieces glued together, then ripped to 2.75" tall matching the height of the rails.
Then holding them in position, determined the proper angles to be achieved to fit well to the plywood support rails. Ripped from straight wood, glued on the angular edges, side edge is 15*, front edge is 3* and this fits well the space matching the plywood rails.

Will fit them in tomorrow. the old rear plywood still has enough left to aid in me designing the new ply support piece. Plan to cut some angled pieces that but up to it to help in making the new rail fit as it should.

 

Have the corner rail support blocks installed. These were difficult to make, every face has a differing angle.
And that rotting mahogany rear plywood support rail is off.
And those posts need replacing.







I screwed 5 angled guide blocks to the old plywood underneath to aid in positioning the new rail. New rail will be cut on a curve then split in half to make the concave bend inward, so the old ply stays on till the new support is fit into place.

 

Have the starboard side rear corner mostly done. Need to and grind down to the proper shape.

In 2001 when I replaced the transom frame and wood, I did not desire to open up the teak decking. So I never could properly finish and seal the upper corners. Now I have.

Cut and fit a filler piece on top the too short inner corner post.



Cut the larger filler piece that also covers the rails and the corner post.



Glued in everything sealed, the rear plywood deck fits into this corner.

 

Here is the multi curved mahogany plywood rail board. This goes under the front edge of the rear plywood, and the teak screws on top the plywood.

Back inside is in pretty good condition.


Bottom view, board is fine here.


Showing the curve hump up,with board propped up.
Top of board is badly damaged on the inside ends.

And somewhat damaged where it laid against the inside cockpit teak covering board. The linseed oil putty had long ago dried out and was hard to scrape clean.
FAIL, oem liked that stuff, but it is a fail.

I used a metal brush and scraped clean all the rotted wood from the entire board. The board still feels pretty strong, so good for a form.


I have been thinking maybe the best way forward, take board to boat and temporarily screw into position. Then laminate, glue with titebond 3 and screw on the bottom thin strips of treated wood, perhaps 1/4, maybe can go 3/8 thick. Build up several layers. Then unscrew the board, take home and on the tablesaw slice off the top layer perhaps a half inch worth. Then glue more laminations on top the board. So a sandwich will be made.

I can also laminate a thin piece to the front to seal the mahogany from rain effects. This board being such an odd shape using it as a pattern is a good idea.

And all my new rails are all taller and wider than OEM. 2.75 inches tall and 1.75 inches in width. Old rails are 2.25 inches tall and 1.25 inch thick. So I have room to add height to this board which can only help.

Why the OEM builder did such small sizes, who knows, the teak covering boards are plenty wide enough to accommodate taller plywood support rails. Just another OEM blunder.
I have even thought of wrapping the repaired board in fiberglass wallboard tape, then smearing PL glue all over it. Would add more strength and better sealing. I repaired a molded plywood chair bottom that way. Somewhere I have a roll of tape.

 

I bought a real nice piece of ground contact 2x10x10.
Very blessed to find it first one I looked at.
No knots, except 2 small ones on other side, which would be cut out if I use this as a pattern.So I will try and cut out a new shaped piece from this and see what happens.


The left side has tight grain, so that would be the humped up part.

 

Board marked out. Wife stood in middle with original curved board on top this big board with curve up.
Then I outlined the edge. Since it was curved up, I lined up by eye pulling the marker perpendicular to the run of the board along the edge.

I then drew another mark next to it to flesh it out to 3 inches in width. Will be carved down to 2.75 when done.



Results, and I may use the large piece at right to backup to this versus the OEM mahogany piece since I don't like woods that will rot. Will give this some thought.



Then split in half on tablesaw to allow it flex into shape, will be glued and screwed into position using the original plywood still in place on the boat.

Before that, I will clamp or screw to the original board and belt sand the top edge to a perfect fit to match. Then also the bottom edge.

 

What adhesive are you using, epoxy and PT materials (lumber, plywood, etc.) don't have a great bond.

 

I use screws and glues like the PL 3x polyurethane and titebond 3.
Most every piece is screwed and glued. I have never had anything just fall to pieces. And the boat does never just spring a leak due to something failing. I use very little epoxy anywhere. I had used some epoxy many years earlier, the epoxy though failed, it came off some mahogany window repairs. I switched to PL and no failure. Epoxy can not yield like PL can which might be significant. Epoxy will just fracture. PL also need sunlight protection, it will erode just like epoxy.

I will likely use the PL to join the split board, A notched plastic putty knife will spread the glue, and the screws will hold it together, the PL is just sealing and adding some strength to the union.
When I assembled the port side gunwale, I did not glue anything together, simply used screws as did oem builder. I dd smear PL adhesive on top and filled with PL and sawdust mixture those frame pockets. I left a small gap for the plywood edges, and did force glue into the gap. But did not fully embed the plywood in glue, I only glued the plywood edges. Doing more than that is a waste of glue.

 

This morn I ground both boards to curve properly to the shape matching the ply edge of the old board. They are not as stiff as the original board. Since the original board is still holding a good curve, I will use it glued in behind these new boards. I will have to repair some sections of the old board.

So the new construction should be at least 50% stronger than new. I am also planning on attaching a 3/4 by 3/4 piece to the top of the outermost new board. This will cradle the new plywood edge.

The builder being dumb, ran screws thru the teak covering board exactly between the mahogany support rail and the plywood. So gluing on a a piece will be better for these screws too.


Clamped along the length plus the new board are 1/2 inch taller than the old one.

 

Today I decided to increase the height of the curved mahogany board to match the other ply support rails. I glued on a piece of ripped treated wood. I predrilled screws to use to line up the parts, then took it apart, glued with Titebond 3, screwed it together.

The ends will be cut off this board to fit between the samson tie up posts.
It will fit behind the new boards that take the original position of this board.

This will make it pretty strong I think. Adds little weight for more strength, not that it needed this. Screwed on arched plywood that sits on top of this adds a lot to the structure.

You're looking at the top of the board, so treated plywood will touch the treated wood.

 

Rain is over a week of rain.

I got the curved pieces in and they fit well.
I backed it up with the original board.



Other side clamped


Screwed in and bolted.
I also cut a rabbit into the piece I put in on 2001 when I rebuilt the transom wood frames. Now the plywood will sit in that supported the whole length. It was easy to do this as that rear board against the top exterior plank was made of 3 pieces screwed together. I just need to glue in a long shim for the ply to rest on at the correct height.







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