Recoring Deck

[tedted]

Well, I have all the goodies gathered and I'm ready to start my recore job on the flybridge deck.

I have done plenty of recoring but have always laid new glass over the coring. I'd like to try reusing the outer skin this time. Both to save time and materials.

Has anyone here recored their decks and reused the deck skins? I am installing Corecell in place of the plywood that is now there. Vinylester resin to secure the coring and then slightly thickened epoxy to remount the outer skin. The epoxy will give me more open time to get everything aligned and in place. I plan on setting weights on the deck to provide clamping force.

If anyone has done this and can give me some pointers I'd be grateful. There's no doubt some pitfalls I'm missing....Thanks, Ted

 

[Max Simmons]

Nothing to add, but may be doing the same soon. Please post pics!

 

[Sailor of Fortune]

No expert but I'd be staying with the Vinylester for the whole project.

 

[psneeld]

Yes I did.
Out with the old, in with new ply, old skin, slathered with epoxy filler, dished the seams and taped them with glass and epoxy, whole flybridge deck then got 3vlayers of 6 Oz cloth and epoxy.

If I had to do over again, the 3 layers of cloth would have been vinylester.

Your plan sounds fine....not like building up a hull.

 

[alormaria]

When I re-cored the walls of my aft cabin sides I reused the interior fiberglass skin. I used epoxy for all the plywood squares and then epoxied the fiberglass skin back over. I needed to maintain the same thickness so the teak and joinery would line up not to mention the aft cabin window frames. At the time (early 90's) epoxy was cheaper than it is now. But still it wasn't cheap.

The thinking back then was that polyester resin only liked to attach itself to other fresh polyester resin. Epoxy will attach itself to anything reasonable including old fully cured polyester resin. I don't know how much that has changed but the more things change the more they stay the same.

 

[psneeld]

Some Vinylester has nearly the adhesive qualities as the lesser epoxies

 

[Simi 60]

Doing similar myself but will possibly use polycore/nidaplast as its a fraction of the cost of core cell.

 

[DHeckrotte]

I've done similar work, but in relatively small areas. Cockpit floor in a sailboat, working from the bottom.

I think you'll need to work out how you get a completely bonded area. Using epoxy with an appropriate filler/thickener, spread with a tile adhesive trowel and then paying attention to how you assure yourself that the shape is correct as you weight/clamp the top skin will do fine. You'd want the original gently curved surface rather than one with excessive waviness.

Replacing the plywood core with plywood would be perfectly sound, and cheaper than someone's fancy core, if the chunks are each epoxy coated in the assembly process.

Finish the cut edges by grinding both the remaining skin and the newly bonded skin to form a scarpf joint, then fill the scarph area with strips of new 'glass. 1:6 or so slope (check me; different slopes for different reinforcements and resins).

 

[Simi 60]

Replacing the plywood core with plywood would be perfectly sound, and cheaper than someone's fancy core, if the chunks are each epoxy coated in the assembly process..

Pre glassed poly core panels here are expensive but not much more than quality marine ply that then needs resin soaking and glassing.

Labour saving is considerable on the former.

 

[FF]

"The thinking back then was that polyester resin only liked to attach itself to other fresh polyester resin. Epoxy will attach itself to anything reasonable including old fully cured polyester resin. I don't know how much that has changed but the more things change the more they stay the same.

My experience too.

Sticking new or old stuff together Epoxy works, building laminate polly is cheaper but prefers to stick to polly.

 

[TDunn]

I would use epoxy for the entire job. Also, if you can borrow a vacuum pump I would suggest vacuum bagging the core and deck panels down. That will give you the most uniform bond.

 

[tedted]

No expert but I'd be staying with the Vinylester for the whole project.

I used 37 gallons of Vinylester on the recore of a Hunter Legend 37. It's super stuff. The problem with bonding the outer skin down is the open time is really short. Much like Polyester Resin. The idea of an hour + open time using a slow hardener is the only reason for using epoxy for that part of the project.

All the rest I'm planning on using the Vinylester. Including the finish taping of the seams. I'm a real fan of Vinylester.

 

[tedted]

Thanks for all the input. It's nice to see all the different methods everyone used.

I'm really sold on both Vinylester resin and Corecell. Vinylester works just like polyester fast and easy. When I researched Corecell I saw that it is used considerably in the megayacht market. Yes, it's more expensive that the other coring materials out there, but considering what a recore job would cost in a shop, the cost is minor. Also, it's touted to have some better properties than the other foams. Can't say any more than it worked out fantastically on the 100 sqft job I did with it. Six years of heavy use and an impact prone cockpit sole fully recored with Corecell showed no problems (as well as all decks 100% dry) when I sold the boat. It really does make a superb light structure. Sorry if I sound like a salesman

One issue I've seen over and over in boats up north in the great lakes especially with plywood coring is the continuous freeze thaw cycles up here. Literally hundreds of freeze/thaws a winter. Once water enters the structure the freezing expands the water. The thaw allows more water to fill the new void created. The tremendous pressure that freezing creates rips plywood coring to pieces. Balsa goes to mush. I was looking for a core that is 100% water repellant. The closest I found was the Corecell. Keeping a deck completely free of water intrusion is a primary concern up here.

An advantage of all the foam corings is they are easily shaped after they are bonded down. A 40 grit disc on an angle grinder makes short work of blending in odd shapes and curves. I ran into a lot of thickness issues when the coring was laid up and I can't imagine the work it would have taken had I used plywood. Also foam cuts easily with a utility knife. Just score deeply and snap it. I had hundreds of small jig saw puzzle pieces cut to do the deck of the Hunter.

After doing that job I will admit that plywood and balsa would serve as well as any other cores. Every core failure I've seen was caused by shoddy manufacturer builds. I made absolutely sure all coring joints were 100% filled and sealed with resin. Even the best boat builders could pay far more attention to core lay up and sealing (that's unseen expense though and doesn't sell boats).

I like the idea of vacuum bagging. I have an old refrigeration vacuum pump and it sounds like vacuum bonding would be a great way to go. I could possibly do a dry vacuum fit to see if everything looks good before applying resin. Interesting....

I'll post some photos as I proceed. I have the swim platform gutted and ready to start a recore and rebuild of that. The plywood core literally poured water on my shop floor. ....but then, it's 40 years old. Maybe plywood ain't so bad???

 

[Larry M]

We looking forward to following your progress. We have a small soft spot by one of the deck prisms and we're trying to learn as much as we can. We'll deal with it in the fall so this is a timely thread.

 

[tedted]

"The thinking back then was that polyester resin only liked to attach itself to other fresh polyester resin. Epoxy will attach itself to anything reasonable including old fully cured polyester resin. I don't know how much that has changed but the more things change the more they stay the same.

My experience too.

Sticking new or old stuff together Epoxy works, building laminate polly is cheaper but prefers to stick to polly.

Interestingly, all the fiberglass skins from the swim platform I'm currently recoring have the outer layer of the plywood ( or what's left of it) firmly bonded to it. The plywood failed at the glue bonds in the wood. I expected to just lift the rotten wood out, but was surprised to have to work pretty hard to get a lot of it out. grinding the woof off the fiberglass has me itching pretty badly...

I found that an automotive style air chisel worked wonders for rough removal. Far better than trying to remove it with hammer and wood chisel.
The air chisel will be my go to tool from now on for getting the coring out.

 

[FF]

"I ran into a lot of thickness issues when the coring was laid up and I can't imagine the work it would have taken had I used plywood."

Remember the stiffness of a cored anything depends on the thickness of the core.

So if say 3/4 ir 1 inch foam is trimmed to 1/2 inch more layers of GRP will be required to maintain stiffness.