I need to join some tanalised planks of wood edeways. The wood is 45mm wide.
Do I have to plane the edges down to untreated wood and then water proof glue them together, or can I glue tanalised without planing ???
Is there any other methods to join them together ??
The joined wood is not going to carry much stress.
I would personally take a circular saw, and make a halving joint in the wood, then glue+screw.
Is it going to be outdoors?
Don't even think about glue in an exterior sitiuation.
Tenon and mortice and pegs maybe..but bolts would be my advice..
If the wood faces are reasonably flat and you can only see, say, 1mm of light between them, then a Polyurethane glue will work well. I would NOT sand or plane the sides to be jointed as a rough surface will bond better than a smooth one - the important thing is that the mating sides should be, well, mating. Polyurethane glue foams to fill minor surface imperfections and is very strong - as it's moisture cured it doesn't mind the damp.
E.G.
Thats what the cartridge said too, but it wasnt my experience. When wet it got a lot weaker, and pulled apart fairly easily.
NT
Thats what the cartridge said too, but it wasnt my experience. When wet it got a lot weaker, and pulled apart fairly easily. Just to clarify, it had to stay wet to reach that point, I'm sure it would have weathered showers ok.
NT
Yup./ It doesn't hold under tension that well..got lots of warped failed glued joints in my oak porch..
Interesting. I've used it for some time without problems. But I'll examine some now you've both pointed this out.
Sorry for the bad advice, stevesmith.
R.
My view is that in exterior situations, glue in any shape or form is pretty inappropriate..it hasn't got the tensile strength, and wood will split itself, let alone glue, when you get wide humidity variations.
The only answer is some kidn if screwed or bolted solution.
Maybe your observation is just as valid. Real world perforance is going to depend on wetness, with constant immersion (mine was on wet ground) vs rain vs sheltered. There are also the qs of the consequences of failure, eg structural vs decorative, and of how much reliability youre looking for.
NT
One of my colleagues made some benches by "laminating" some boards together. He used some very long, thin screws with wide thin flights. They didn't split the wood and could be driven with no pre drilling. They seemed well over 20cms long and had a catchy name but I just cannot remember it.
AJH
Strange, then, that a lot of wooden boats are built using glue.
Perhaps the difference is that boats tend to have other protection such as paint or varnish, but I suspect a lot of outdoor woodwork such as hardwood patio furniture is also glued.
My old clinker built dinghy had various glued bits, and had to be soaked at the beginning of the season to become watertight, so I don't think that having the wood constantly damp rules out gluing either.
Perhaps gluing softwood with no protection against becoming waterlogged then bone dry on a regular basis might destroy a glue bond because the glue will not expand and contract with the changes in moisture.
On the other hand, marine ply is glued together, is it not? Also exterior grade ply?
Perhaps the wrong wood and/or the wrong glue are being used in this situation?
Cheers
Dave R
Indeed. And they use very stable wood..usually plywood..which has its own very carefully formulated glue in it..never tanalised building lumber!
AND they are definitely given many many coats of very tough paints and varnishes, which need regular maintenance.
If it needed ti be soaked to make it watertight, then the planks weren't glued together were they? and you have proved my point that planks move hugely under humidity changes opening up gaps..no glue would seal those clinker planks together..you caulk a and wet and hope..
The frame? well a GODD piece of planed wood with proper joints and a synthetic resin glue will take immersion for a while.. but traditionally all boat frames were 'one piece' wherever possible..even down to selecting curved branches for the parts.and tenoned and pegged..
I think the first glues that really worked for boats were cascamite and aerolite 306. Glues that set and were of a plastic variety..but t even they won;t hold up it the wood becomes sodden.
They hardly expand at all. The issue there is the cross graining..you get about 3-5% expansion across the grain, and almost none along ot. Cross bonding locks the cross grain stiff in place hard..those plies are made under pressure and heat on presses using very tightly controlled gluing. They are very stable. Probably less than 0.1% movement in any direction once made.
Yup. Tanalised lumber is simply crap wood given an anti-fungal treatment on the surface layer. Its got no water rejection properties at all and it moves like a bitch under humidity cycling. Depending on how its fit it can warp,cup and shrink all over the place. Tying it down will like as not result in in splitting if the section is small enough..or even if its not.
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