Deck re-core from below

[sailingunity]

Originally Posted by s/v Jedi

Balsa is fine but no deck penetrations. There shouldn’t be a core material at the stanchions to start with, the core in deck and hull should be tapered out to a solid area around the deck/hull joint that has enough room for the stanchions.

Again, my recommendation to try to put the balsa on the cut off skin first. You can use some hot glue while fitting. Also, simple to repair the cut off skin.

That sure sounds nice, but to reproduce the 5/8 thickness (core plus skin) would require something like 18 layers of 1708? How do I lay that up from below in any reasonable amount of time?

I've attached a drawing of my deck profile. There is a toe rail about 3" high, this is made up of the top deck rising up to overlap the hull, this interface is glassed together from the bottom side. The stanchions do sit on raised bases that are solid glass, but they are cored below that.

Since I probably have 12-15 feet of coring to replace here, are you saying that the glass should taper as you describe the entire length of the joint, or only where there are stanchions? If only at the stanchions, can I just use a piece of G10 underneath them, or is it important structurally to have the glass tapered in?

[s/v Jedi]

Originally Posted by sailingunity

That sure sounds nice, but to reproduce the 5/8 thickness (core plus skin) would require something like 18 layers of 1708? How do I lay that up from below in any reasonable amount of time?

I've attached a drawing of my deck profile. There is a toe rail about 3" high, this is made up of the top deck rising up to overlap the hull, this interface is glassed together from the bottom side. The stanchions do sit on raised bases that are solid glass, but they are cored below that.

Since I probably have 12-15 feet of coring to replace here, are you saying that the glass should taper as you describe the entire length of the joint, or only where there are stanchions? If only at the stanchions, can I just use a piece of G10 underneath them, or is it important structurally to have the glass tapered in?

I don’t understand you. Put the skin on the bench. Fix it with a layer of 1708 on top (which goes against the core) Put the 1/2” balsa on top and try for size. Maybe add another layer of 1708 and try again. When it’s reasonable, use epoxy to adhere the balsa to the skin and do final fitting. It should sit just a hair too far in. Now take a piece of plywood that spans over the spot to reference against the surrounding deck fiberglass that wasn’t cut away, cover it with plastic foil, put the skin + core combo on top and wet out the balsa as well as the cavity up in the deck with unthickened epoxy. Now add colloidal silica filler to thin peanut butter consistency and use a notched spreader to coat the top of the balsa and take the whole thing up and apply pressure to the underside of the plywood to get a perfectfit and let cure.

[s/v Jedi]

About the stanchions: yes, where the stanchions are there shouldn’t be core. So with my method described above it is easy to replace that part of balsa with a suitable core material like Coosa board or one of their knockoffs from your local fiberglass supply. You’re working on a bench with gravity assist so it’s easy to get right.

[sailingunity]

Ohhh I see, sorry I misunderstood you. So you're saying to do all of the prep work with the skin and the core on the workbench, and then just bond it up in place as the last step?

Not a bad idea, though I may have messed up a bit as I was doing some exploratory cutting, my first hole was maybe 12x12, which wasn't big enough to get all the core side to side, so I cut 2 more small pieces out to get to the rest of it. Now that I know the core spans all the way from side to side, I'll probably do better.

[s/v Jedi]

Originally Posted by sailingunity

Ohhh I see, sorry I misunderstood you. So you're saying to do all of the prep work with the skin and the core on the workbench, and then just bond it up in place as the last step?

Not a bad idea, though I may have messed up a bit as I was doing some exploratory cutting, my first hole was maybe 12x12, which wasn't big enough to get all the core side to side, so I cut 2 more small pieces out to get to the rest of it. Now that I know the core spans all the way from side to side, I'll probably do better.

No problem, just glue it all together on the bench. The piece of 1708 will nicely bond it all together.

Everything that isn’t done from above is done this way by professionals, incl. vertical surface like the hull, where they simply screw the plywood presser-board to the surrounding hull. For working from underneath you can add some screws but surely need to put struts under it as well or it will sag down.

I have seen one guy put 10 layers of fiberglass, each one that went on bigger that the previous one, all wet out on a plastic sheet, then put a plastic sheet over it, followed by the plywood presser board. I helped him taking up the plastic sheet between table and patch, flipping it around, then carry the whole thing, holding the plywood like a serving tray to the boat and slap it on the hull where a hole was. Some drilling and screwing and let cure. When plywood and plastic came off it was beautiful and only needed sanding to remove excess resin…

Knowing this was a pro but after that hands on I know any handy fiberglass DIY guy can do it.

[sailingunity]

Thanks for the advice Jedi, I've got my eye on something like this to hold the board up, I plan to remove coring in about 4-5 foot sections and replace, then move on to the next area. With the boat being 50 years old, who knows, I might be replacing all of the coring.

[s/v Jedi]

Originally Posted by sailingunity

Thanks for the advice Jedi, I've got my eye on something like this to hold the board up, I plan to remove coring in about 4-5 foot sections and replace, then move on to the next area. With the boat being 50 years old, who knows, I might be replacing all of the coring.

I don’t like it. I take a piece of 4x8 and screw a small scrap piece of plywood onto one end to go up against what needs to be pushed, then on the bottom end I use a small hydraulic bottle jack so I get easy adjustment. It’s cheaper too

Edit: for 5 foot sections I would use two of those. They give them away for nothing at Harbor Freight.

[sailingunity]

Originally Posted by s/v Jedi

I don’t like it. I take a piece of 4x8 and screw a small scrap piece of plywood onto one end to go up against what needs to be pushed, then on the bottom end I use a small hydraulic bottle jack so I get easy adjustment. It’s cheaper too

Edit: for 5 foot sections I would use two of those. They give them away for nothing at Harbor Freight.

Seeing as I don't have a bottle jack, this seemed good. Why don't you like it? The piece of plywood would go on this jack. I liked the reach, that I could put the bottom on my workbench and the top will support the work, without having to fuss with stacking stuff.

[Fore and Aft]

Sailing unity l assume you drive to the boat so why not use the jack in your vehicle? The only issue with a jack is don't put a bulge in the deck. I also like some 4x2 props with wedges, all cut and sized well before the resin is mixed.
Cheers

[Ratty1978]

I recored from the inside on a 24 foot boat by drilling many holes, letting the rotten balsa do whatever it did when oxygen hit it, left it long enough to dry, and then used syringes (there are big 50 ml or so ones that fit 1/4 in. holes) to inject epoxy with filler. Heavier than balsa, messy since its overhead (used duct tape patches to cover the holes as I went) but it worked. Since then I've recored a different boat and decided that its better with gravity on your side. Had to use balsa because of class rules. No worries getting good coating and adhesion there. Gaps letting water in are the problem. Might you be able to use a jack from the inside to compress things up? Maybe, but you need compression for a good bond and a less than complete bond is what gets balsa to get wet and delaminate. By the way, on that second boat (about 40 years old) there was some wet, but not yet rotten, balsa that was tough to chisel out. Consider shrink wrap to create an impervious work space and work from the top. Easy for me to say because I'm in a place where we pull the boats out of the water for the winter.

Originally Posted by sailingunity

My 48 year old boat has had a somewhat inconsistent and pestering leak on the port side for a while now. As far as I can tell, the previous owner had issues with it as well and never could nail it down. I've rebedded hardware in the immediate area to no avail, as best I can guess the leak must be coming from somewhere "uphill" on the topside, and running horizontally inside the deck until it gets to an opening (which happens to be either above my workbench or in the aft cabin chain plate area).

Over the years, this has rotted out a good portion of the coring, as evidenced by the hollow sound of approx. 8 feet of side deck. There are no soft spots, per se, but my stanchions do move slightly as I walk down the deck.

My plan is to cut the skin out from below and remove the rotten coring, then see if I can pinpoint the leak. Reason for going in from below: I live in FL which gets rain almost daily, and this project will take me several weeks as I only have about 4 hours each Saturday to work on it.

I'm not quite settled on what to replace it with. I've read varied opinions on how how great / awful foams are, as well as how great / awful balsa is. Though I'm not super inclined to go with Balsa again, I can admit it has good physical properties and it's cheap. Alternatively, I thought about H80 + Coosa or G10 where reinforcement is needed (like the stanchions). It does seem like it would be easier to apply a board from the bottom than the mesh backed balsa.

Anyone care to change my mind?

[s/v Breakaway]

Before I knew that repairing rotted core was as difficult as you guys make it (!), I repaired a section of the cabin top on my Cal 34 from below. A leak had been allowed to exist under a winch by the PO that rotted a section about 20" x 30." I determined the area to be repaired by drilling a few small pilot holes after I removed the vinyl headliner. I then set my plain old circular saw to a shallow depth and cut out the section. I scraped out the rotted core, found a piece of plywood of a compatible thickness, cut it to size, buttered heavily with thickened epoxy, pushed it into place, and propped it up with several poles. After the epoxy cured I applied a two layers of epoxy-wetted fiberglass cloth. After that cured, I replaced the headliner.

Twenty years later, it is still doing fine.

Just sayin'

[s/v Jedi]

Originally Posted by s/v Breakaway

Before I knew that repairing rotted core was as difficult as you guys make it (!), I repaired a section of the cabin top on my Cal 34 from below. A leak had been allowed to exist under a winch by the PO that rotted a section about 20" x 30." I determined the area to be repaired by drilling a few small pilot holes after I removed the vinyl headliner. I then set my plain old circular saw to a shallow depth and cut out the section. I scraped out the rotted core, found a piece of plywood of a compatible thickness, cut it to size, buttered heavily with thickened epoxy, pushed it into place, and propped it up with several poles. After the epoxy cured I applied a two layers of epoxy-wetted fiberglass cloth. After that cured, I replaced the headliner.

Twenty years later, it is still doing fine.

Just sayin'

Exactly. The question is if you wetted out the fiberglass on a bench or against gravity straight underneath the deck?

[s/v Breakaway]

Jedi, I wetted out the fiberglass cloth before I applied it to the plywood. I used smaller pieces as there was no way for me to hold a 20" x 30" sheet in place. With the piece of plywood, I buttered both the underneath of the deck and the top of the plywood before I pressed them together.

[col50]

Originally Posted by mike d.

6-10 is a premix in that it is 2 tubes attached together so equal amounts of hardener and resin come out equally, and it is thick so you don't have to add micro balloons etc! you just squeeze it on in a cross patch pattern with about a 1 inch spacing depending on what your doing ! Push it up down, what ever you are doing ! when you push it into position depending on the curve of the work it squishes in all directions and covers the whole area of contact ! All things being equal that is what it is supposed to do ! You never really know if you make full contact, but when I went back on deck after application and tapped the deck, there were no dull sounds anywhere, and surveyor agreed ! Other than cutting out the repair you can't tell if there any voids ! But I brushed on regular West system to wet out the core ! Sounds like doing extra, and maybe it is, but it was easier than mixing a thickener !

Why not put the thickened epoxy on the new core instead of the underside of the deck?

Wouldn't that be a lot easier?

[foufou]

I wonder why no one has mentioned vacuum bagging? It is not all that difficult to implement and ensures a void free result with a sheet of plastic film, some breather material can can be as available as carpet backing material, peel ply that I have substituted with rip stop nylon, some plastic tubing, some butyl tape, and a vacuum pump or even a shop vac. While not using such a setup may work well, vacuum bagging ensures the absolute best result. It might be particularly useful on curved surfaces.