Do I re hydrate hull before new caulking and paint?

The great stuff construction adhesive sounds interesting. The data sheet online was less than informative. Not saying it isn't a decent product, but the information provided was useless. There is a similar competitor with a better data sheet. I haven't used either of them. The Advantech stuff I jest read about in Fine Homebuilding this morning, so one ad and no hands on. Neither foam mentions flexibility, which I would like to have seen. PL premium, as stiff as it is, still has some resilience.

The Nov. issue of Fine Homebuilding has a decent article on the newer, less durable green in the political sense green treat yellow pine. Not your grandfathers PT pine. Only the foundation grade .60 CCA is something I would recommend for boats. It is special order and comes in limited sizes. It is not allowed for interior use on homes, but good for deck framing. The building codes are now requiring that the cut ends have to be treated with something like copper naphthenate. There is a small market for all wood house foundations, which do last if done properly. I hope so anyway as mine is 35 years old. If this was Australia, I would recommend turpentine, the wood, not the solvent.

I have used some of the various Great Stuff gap filling foams. They are very light, the tds says 14 psi tensile strength and 1 lb/cu ft density. The advantech subfloor claims 500 psi shear and I could assume great stuff might be similar. They tend to form very large bubbles in thick sections. In my experience, when they dry slowly the bubbles coalesce, which makes for larger voids. I fooled with some on a foamy trailer topper for a utility trailer, just to get a feel for foam structures and how to build a small camper. The Great stuff landscape foam seems to be stronger than the gap filler. It costs more, but it seems more durable. I would not consider the gap filler for planking, but that's just my opinion. I'll go as far as maybe on the landscape filler, but would be more confident in the subfloor adhesive but I have not tried it.

Another foam that has garnered a poor reputation for open or lightly clamped joint strength is Gorilla glue. It also forms very large bubbles in gaps, but that can be controlled to some extent by adding some wood flour and or fumed silica. As a gap filler, it may have some, albeit messy, utility. Still not a flexible foam. It does fill nail holes and cracks reasonably well, and with silica it is noticeably harder. Just for grins, I tried a gorilla glue/fiberglass composite. Epoxy it isn't, but for a quick and dirty sawdust vent elbow on a radial arm saw it was adequate. I wanted a way to attach a dust collector hose. The inside of the shape was carved from styrofoam. It was wrapped in fiberglass with some slightly wood flour thickened gorilla glue. There isn't much foaming since it was thin and the gas could escape. The styrofoam disappears with acetone. It worked well even if it does look like dung. Not a glowing recommendation, but in an 18 oz bottle it isn't any more expensive than epoxy. Another tool in the box for mickey mouse repairs. Gorilla glue doesn't age well since moisture in the air can get through the bottle and thicken it. Use it or loose it in a matter of months, so I used it up.

 

I am starting to think even PL Premium poly is too hard so not ideal for plank seams. So am thinking of Great Stuff, the 1" sealer. I don't need a seam sealer since I coat the entire wood hull. But I do need a caulk that is there as a base for the coating that goes over top. And I do think as the planks swell, you want them to be able to swell and not be restrained and crush the edges, causing more issues as it ages. People need to experiment! And try out new ideas, I plan to try it on a few test seams on my boat. I don't see how it could fail me anyway, and it would be cheaper and easier as a caulk for planking for others even if they don't overcoat the wood with a sealer coating. Logically it makes sense to me how it would work.

For example, I am near several Chesapeake Deadrise wood boats, and they tight edge but pine or juniper 2x planking right next to each other. And I never seen them ram any caulking into plank seams and these are old boats. They just go back in and swell up and seal ok. While all these hardwood thinner planked boats are all made to be caulked and the edges wear out over the years. I am thinking the act of hammering in the caulking is contributing to plank damage and making the problems eventually much worse. It is just the way it was done, and so it is just the way it is done, kind of like inertia.

 

I see your point about filling with soft friable foam. Your results will be interesting. The wood will expand and contract with humidity to some extent no matter what you do. It can't be completely prevented, but it can be reduced considerably.

Butt joints aren't affected much by moisture expansion as detailed below. If you weren't talking about butt joints, there was small boat at the Chesapeake Bay Maritime Museum that was swamped next to the dock so that it could 'take up' and seal the joints. It didn't appear to have any caulking. I have heard that you can run a tool like a screen spline roller on the edge of a soft wood plank, then plane down to the bottom of the groove. When it gets wet, the compressed wood sells to form a ridge that helps seal the joint.

The computer copied a lot more than I highlighted.

 

What people need to understand is brand new wood boats back then never had these humongous opening plank gaps, all that damage happened over decades of use, hauling out, drying out, then more caulking rammed in between planks, poor planks had no way to expand, so the edges crush or the fasteners can even pull from frames as the wood takes up. Over and over again. And wood boats 'work' plank against plank in the water as in going through seaways, the planks actually rub each other and wear themselves down. I don't know if you have noticed, but the beveled plank edge cut for a caulking groove tends to grow wider and wider, while the inner plank edge does not suffer the same level of damage. The opening gap on the outside plank edge grows wider faster than the inner plank gap grows. I can only attribute that to the hard caulking in that space causing more edge compression than the inside plank edge. I suppose the act of using a caulking iron tool to hammer in caulking also is having an effect on the outer plank edges.

 

The fibers on the plank edges compresses to the point that the cells get crushes and won't swell back to the original size. That is a well known phenomenon. One of the easy proper repairs in to open the sems with a saw and then glue a spline to one of the edges. The seams gets tighter so it can be properly caulked again. These are ancient methods that have been proven to work well.

 

What is needed if you do not glue in splines and go conventional hammered in caulking, is a soft gasket between planks that allows sealing, no leaks, dry and wet and can allow planks to take up without excessive edge crushing. If frames and screws are in good condition, now I did not experience the boat losing any PL put in seams like some people complain of with 5200 in the seams coming out, but I also dont know if they put 5200 in filthy greasy seams priorly stuffed with toilet bowl wax rings, tars, linseed oil or whatnot which contaminates the wood surface. I think the expanding closed cell foam is an interesting idea. Construction foam or the other one as a test, will do that to some seams this haul out. Those foams do have adhesive qualities and are waterproof.

On my boat, the inner planks edges always have touched tight no gap after being in the water for a while, even polyurethane coated, planks take up some moisture and swell a little. But the caulking gap filled with PL remains as it was. They are the original mahogany 4/4 planks 54 years old.

I also think since I have been coating on top with polyurethane type coatings, the planks get locked into an embrace where sliding past each other does not happen as the boat moves thru the waves, a hull will twist and planks will slide past each other a tiny amount, which over time, rubs them down. Coatings like that do spread the forces across the entire hull rather than localized. Not as monolithic as fiberglass does as it is rubber like. But it does contribute to the hull holding together more as a unit versus a looser collection of boards.