Timber Boat Caulking
Traditional cotton / oakum caulking tips for timber planks — and why hard sealants often do more harm than good.
A Word of Caution
We are not boat builders or shipwrights. Always consult a professional before undertaking structural or seam work on a timber vessel.
Why hard sealants often fail on timber
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 and need to be replaced. 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
1. Pack the seam
A vessel is caulked with Caulking Cotton or Oakum (for larger planked vessels or bigger gaps).
2. Dress, prime and paint
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, and some might use a dollop of Lanolin Grease (to stop it from going hard). It is then primed and painted.
The guide linked 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.
Further reading and local shipwrights
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 its place. Many thanks to WikiHow for the informative article. The Boat Works Gold Coast have three or four excellent shipwrights as tenants within the complex — if you would like a professional to do the job for you, their trades contact details are listed on their site.
How to caulk a wooden boat (WikiHow) Shipwrights at The Boat Works
Shop caulking supplies
We stock caulking cotton, tools and related boatbuilding supplies in store.
Questions about timber caulking?
Call or email the shop and we will point you at the right materials.
07 5500 0002 · shop@marinetradesupplies.com.au
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