We often come across boat owners with timber boats chasing 3m 5200, Sikaflex and various sealing solutions. The majority of these type products cure quite hard and are not flexible enough to allow the timber when immersed in seawater to swell or “taking up” water as it’s called in the trade into the timber. Hardwoods will take up less water than other softwood timbers. Over caulking as well as non flexible products inserted into the seams will cause damage where planks will even split & need to be replaced. Bear in mind we are not boat builders or shipwrights, and we always suggest you consult a professional before undertaking such works. A quick search on the internet will reveal a plethora of traditional boat building methods and information to guide you in the right direction.
Caulking is a two step method. A vessel is caulked with Caulking Cotton or Oakum (for larger planked vessels or bigger gaps). Once caulked, it is then dressed with a home made compound, generally containing a mixture of Linseed Oil Putty, antifouling (in lieu of red lead) to stop the worms & some might use a dollop of Lanolin Grease (to stop it from going hard). It is then primed & painted.
The article below also mentions putting a primer between the planks prior to caulking, some prefer a timber sealer inside the seams like International Primocon to protect the timber. Unfortunately Interlux Seam Sealer is not available in Australia. At the end of the day, common sense and following correct procedures will allow you to complete your project and as you learn you will fine tune to your own end.
The article below is a good simple explanation and although red lead is no longer available, some mix a little antifouling paint these days in it’s place. Many Thanks to Wikihow for the very informative article
The Boat Works Gold Coast have 3 or 4 excellent shipwrights as tenants within the complex, so if you would like a professional to do the job for you, try their website where the trades contact details are freely listed here: The Boat Works Gold Coast