I want to join some chunky pieces of green oak together to form a bench. Looking at the Screwfix range of Coach Screws the options are either "Stainless Steel" or "Outdoor Green Corrosive Resistant". I want to avoid marking the oak so would normally have gone for stainless steel, but would the green corrosive resistant ones be any better?
Thanks for any advice, John
Treenails, not steel at all.
No, Even stainless isn't brilliant (depends on the grade - if you can make screws out of it, don't trust it)
If you want nails, pay for bronze ones, or else use cheap copper roofing nails in drilled holes and rivet them at the back
I think "outdoor green" means "zinc plated" - in which case go for stainless. IME green oak is very capable of attacking plating.
If you want to be a bit more ambitious, google using the draw-dowel method of using oak pegs - the traditional solution of jointing green oak, and the joints can be tightened up as the beams shrink.
Thanks for that. I'll done a bit of reading up and will give the oak pegs a go. I also need to need to fix the oak to some masonary so will stick to the stainless steel for that.
One nice way to do that is with steel tenons poking from the wall (strip welded to a plate, or just buy ready-made staples) and then hiding them inside a mortice cut from the back of the oak. Peg through the sides and through the loop.
My experience with stainless steel and oak is that the acids in the oak attack the steel rapidly. Stainless steel relies upon a coat of oxide for corrosion resistance and if you exclude air (as happens when the screw is inserted into wood) and provide an acid environment that coating is dissolved and cannot reform. On wooden boats this is familiar and leads to crevice corrosion with consequential failing of the stainless fastening.
The green coach screws sound better, but if you want longevity the coating on these screws is rather thin and will fail eventually.
The solution on boats is to use either bronze coach screws (expensive) or heavily galvanised screws, usually sold as "hot dipped". The latter are available at farmer's merchants such as SCATS because they are commonly used on farm gates.
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