Glue

If the bar is open to discuss vacuum bagging, I'm coming over.

 

General boating topics accepted. Superb workmanship and artistry.

 

Nice bar.I have to say that when I have vacuum bagged wood,it has only really succeeded when I use an envelope bag or have an impermeable surface beneath a flat job.Wood itself never gives me a good vacuum.

 

I assumed it had less than 0% chance for the vacuum clamping to work on a hull and was just a dry clamping process. But no harm no foul.
We used glues with a anti slip agent additives for most veneer work. I think it add to most glues these days.

As for glueing oak with different glue types.
Water base glue would be a Non- Spontaneous chemical reactions that require an energy input to proceed (dry and penetrate the wood structure) and it cannot take place without the influence of external factors. (Presser and heat)

Epoxy glue would still be Non- Spontaneous and would require less energy input or less presser/heat to complete the drying process because of the heat being add to the system by the chemical reaction between the two parts resin and a curing agent.

Just easer for us to use epoxy because it takes less presser/heat for it to dry and penetrate the wood structures.

Watching glue drying through a Gibbs Available/Free Energy Equation.
Δ G = Δ H − T Δ S
Gibbs available/free energy (ΔG)
Enthalpy change (ΔH)
Temperature (T)
Entropy change (ΔS)

 

Back in the early days of the Gougeon Brothers they adapted the acronym W.E.S.T. as being Wood Epoxy Saturation Technique.
It wasn't long before they had to disavow the "Saturation".
Epoxy doesn't "Saturate" wood at all, it can basically only penetrate to the first layer of unbroken cell structure.
They were good businessmen, they figured out a way to get the epoxy packaged in small enough quantities for the backyard guy and the tradesman, and offered a thinner viscosity that was more user friendly.
Back then it was made by Shell Oil, its trade name was "Epon", and Shell was making it in tank-car lots and 50-gallon barrels.
Others had tried to market it in small quantities but couldn't "crack the market", so to speak.
I remember seeing ads for "Shell Epon" in the late '50s, early '60s.
You can still buy Epon resins/hardeners.

 

I switched over to Urea glue in the early 90s. It has a learning curve short shelf life less than a year, power must be kept a room, precise mixing ratio.
Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure, thermosetting resin or polymer.
Invented in the 30s, used in hot molding, was used in WWII. I have been trying to find if it was used in the The de Havilland DH.98 Mosquito but was used in boats. I have an 1954 mahogany Jet 14' one class made in a hot molded process and the wood just doesn't rot.

 

A quick search found contradictory reports of the glue used in the Mosquito this one says resorcinol BBC - WW2 People's War - Mosquito glue invented in Ewell - Was it a Mosquito that crashed on the Downs? https://www.bbc.co.uk/history/ww2peopleswar/stories/33/a7336433.shtml and this one says urea formaldehyde The Mosquito Fighter-Bomber Did It All in WWII, Quickly Amassing a Combat Record No Other Plane Could Touch https://www.historynet.com/the-miraculous-mosquito/ .My father was in the far east during WW2 and saw the damage that termites could do to them.We have a lot of survivors of the hot moulding process still in use an I have to wonder if it might be attributable to the heat of the process not only driving out some moisture from the wood,but also perhaps pasteurising it by eliminating any organisms present and leaving the lignin and xylonite sealed in by the glue film,I have suspected that the capital cost of a boat size autoclave was the reason nobody seems to have used the technique after the war surplus equipment was retired.I am curious about whether a high vacuum inside a bag would suffocate any organisms present in the wood and I am fairly sure that modern epoxies will be stronger than the more traditional adhesives.

 

I had ants eat part of the adjoining mahogany structure of a hot molded hull. Mostly the 2 part keelson that sandwich the two half of the hull together of a bilge less hull.
If the glue or a finishes is to thick becoming brittle and can not flex with the wood as it expands and contract. That is why epoxy can be used successfully in a small shop without a good jointer, planer, or a lot of clamps.

 

It seems there is some confusion between the cold and hot molding processes used historically in aircraft production. This probably stems from the use of common brand names instead of the full designation or at least the chemical family.

The Mosquito fuselage was not hot molded, it was cold molded. The initial glue was a casein one, then they switched to a UF glue. Both are classed as water resistant, not waterproof. UF glue will polimerize at room temperature but heat greatly accelerates the process, reducing clamping time. The Mosquito assembly lines used mainly electric strip heaters to accomplish this.
At the time the UF glue was only available in a two part form, the resin and a powdered hardener, today its also available as a dried powder mix wich is activated by mixing it with water. In this form it is known to modern woodworkers as plastic resin glue, produced for example by Weldwood.

During the same time frame there was another process already in use before UF glues were invented for producing aircraft laminated parts (wood and wood metal), involving a different glue family, the PF's. This is essentially a form of bakelite, and requires high temperature and pressure for curing. This was commonly done by using a steam autoclave, and this equipment was later used for the production of hot molded small boats. Small boats only because the autoclaves were sized for propellers and aircraft control surfaces, not fuselages. The glues from the PF family are classed as waterproof, and there were several types and formulations available. Google Tego film, Duramold and Redux for historic references. This is the glue you see today in all exterior/WBP plywood.

Also during WW2 another glue family was invented, the PRF's, aka resorcinol. This is a waterproof glue that requires high pressure but much lower temperatures (about half) then PF's for polymerization, and is classed as a cold molding glue. It was widely used in boatbuilding before epoxy became common and is still available today as a specialized woodworking glue, altough its use has declined to the point where small customers have to actually check the expiration date of the batch when they buy it, or preorder and wait.

 

Modern veneer adhesive guide:
Veneer Glue & Adhesives for Vacuum Pressing and More https://www.joewoodworker.com/veneering/glues.htm
A lot of FAQ for glue and process for veneers and DYI kit for vacuum presses systems

 

I have read that West System G-flex epoxy was made to work better with white oak than prior epoxies as white oak and epoxy can de-bond, seen it myself on my own white oak keel, and it failed dry, never getting wet. Specifically, I was epoxying in 1/2" face plugs to hold bronze screws drawing planks, the epoxy failed, and the plugs pulled out when screws were tightened up. I found that highly alarming. I used polyurethane glue, and the plugs held in the white oak keel.

As I worked and gained experience, I found out bamboo chopsticks like from a Chinese restaurant when coated in polyurethane adhesive waterproof glues and hammered into worn or damaged or too big screw holes, held screws like it was new wood. And have held the last 20 years for a splash rail and some planks. Hammer in as many into a hole as you can. I am not talking using hardwood dowels. The bamboo allows the screw threads to bite into it.

White oak, mine at least, is different feeling than red oak, it is oddly more slick to me. Whereas red oak you feel the sanded surface roughness, it just feels different to me.
It could be due to the nature of the wood being much less porous, whereas red oak is like bundled straws bound together. Red oak channels water into itself, so I suppose it also sucks the glues into itself a lot. Due to that it rots easily.

 

You can hammer any piece of wood, even without glue, in an oversize hole and the crew will bite into it.
All wood is like bundled straws bound together, it is the structure of wood.

 

You can use dowels, I have been told by lots of folk they are not as good due to the grain direction, it is like a screw turned into end grain wood. Wont hold as well as face grain wood.
My sense is that partially depends on the screw threads, how well they can get into the wood fibers to grip, and the wood type used.
Opinions vary on this, longer screws would be better for end grain.

screwing into end grain - Search

 

I think that end grain works better. The wood splits and wedges into the hole. It is the way trunnels work, but instead of a wedge of hardwood you are using a screw.