Delamination, Core Options

[Spence]

I will be replacing about 8ft of core material on the starboard gangway. I guess it's had a lot of traffic over the years with 250lb guys running back and forth on it. It's a non slip area about 10" wide. I'll be working from inside the cabin which mean working on my back. I'm not confident on the quality of my work to work from topsides and remove the top skin.
I was thinking of replacing the rotted balsa with 9mm Marine Meranti ply at 106$ a sheet. Another option is outdoor Overlay Signage Plywood at 60$ a sheet, which is not 100% free of voids, but is an outdoor commercial sign material and the seller says is better than ourdoor fir ply. I can vouch for the long life of this material. I have a piece for the bottom of my lawn tractor trailor that sits outside in all weather. I built the trailer in 97 from 1/2" board, and it was already a 1982 sign.
I could also saw a million 3/8" eastern cedar qtr sawn ends out of a 2 X 8, then clamp them all to make a large surface, but that's not practical.
You guys see anything wrong with using this marine ply for core material?.

 

[mitiempo]

Plywood is the worst core material. Very heavy for its compressive strength. Also if any water gets into the plies it travels easily throughout the area. Better choice would be end grain balsa or one of the foams used for core.
Very hard to get good results from below, even for a professional. Vacuum bagging will give the best results.
Working from the top with gravity on your side is really the best option.

 

[Gunni]

And when you get ready to resin that core into place while laying on your back below the work area? Do the job from above, preserving the bottom skin to contain your repair resin. There are worse things than having mis-matched non-skid. Have some balsa deck core shipped to you.

 

[Spence]

I could remove the top skin by making a dremel cut in the smooth boarder. I would install the core, and that would easier bedding the core to the skin, but my concern is that when replacing the top skin, it makes a butt joint with the non skid area, not a 1 to 12 overlap joint has is suggested in FG joinery. In time with all the flexing I'd have a linear crack running the full length. If I want a perfectly flat long lived transition between skins, I'm still stuck in working a joint under the two laminates to sister the two mating edges. I know it is doable, but with more cosmetic work. I can be more sloppy working from the bottom. I may do the top option anyway.

Thanks for the help.

 

[Gunni]

Yes, you will need to overlap the glass over the properly prepped adjacent deck and fair the resulting repair prior to applying paint and non-skid. Tape off your work areas and keep things neat to minimize fairing and sanding. Make no mistake, deck core replacement is a big job, why spend all that time and effort and not have it be durable and right?

 

[Charlie Jones s/v Tehani]

I recored the side decks and bow section of my boat from below, using marine ply. Not as easy as from up top, but doable.I fitted sections as large as I could handle, buttered with epoxy and wedged them up to the upper surface. After it cured, I glassed over with a several layers of 10 oz

 

[Charlie Jones s/v Tehani]

Rebuilt the rotted balsa in the cockpit sole using KledgeCell and epoxied the original top layer back on.. That was in 2000 and it's still doing just fine