On a recent post, I was advised not to use Polyurethane glue on an external structural frame. (150mm square posts to 227mm deep Glulam beam)
Somebody mentioned using an epoxy glue ... any recommendations (avail in UK)
On previous structural jobs I have used Cascamite ... is there something better ?, a gap filling or expanding glue would be preferred (but may not be possible)
I think you would do well with two-part epoxy with an adhesive filler. Check out
What's wrong with polyurethane? It is rather cheaper and easier to use than epoxy. Not as strong as epoxy, but as the joke goes; either is stronger than the wood, so what does it matter?
I was going to do a new post on this subject after a weekend's using polurethane and ask if there is a viable alternative as I find it horrible stuff to work with - sticky and doesn't remove easily - and all that blasted foaming out of the joints.
Rob
Two months ago I did a test. I glued poplar with epoxy and Guerilla glue. I soaked them in a bucket of water for a month. Niether came apart. I tried to hammer both apart and they are staying together.
Not a scientific test, but a test.
IIRC, polyurethane glue is subject to UV degradation but the same is true of epoxy. I'd use the poly but a construction adhesive formulated for exterior use should work too.
Jess.S
Neither polyurethane nor epoxy will last well outdoors, owing to UV degradation.
However it's easy to make epoxy UV-resistant by mixing it with a cheap opaque filler, such as chalk dust (whiting).
..or cover it with something.
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Like wood?
Same with polyurethane. Paint it or cover it with trim.
Like polyurethane. Umm... varnish, that is.
Mike
Sikaflex 221:
or have a look at the rest of the range.
Alternatively Marineflex is much the same, and quite a bit cheaper if you buy it direct by the case:
cheers, Pete.
For maximum strength, polyurethane glue also requires woodworking or furniture quality surfaces and joints. It is not gap-filling like epoxy is; it may foam up and fill a gap or void, but it will not have any strength. Epoxy will maintain it's strength even with a relatively poor fit. On a construction project, that is often what you get. OTOH, there are poly construction adhesives that come in a tube; The are similar to liquid nails in consistency. I've used some of these; PL1 brand claims to be 3 times as strong as "conventional" construction adhesives (like liquid nails?) IIRC
But Sikkflex 221 is a polyuretahne glue ... which others advise is liabel to UV degradation, and while gap filling is crap when there is a gap ? i.e. not a furniture grade joint.
what will last well out doors ? (excluding a home mix as described )
Do you know of any ?
Interesting follow up .... I contacted several major glue manufacturers ... the fact that has come out is that Epoxy is NOT suitable for external wood joints, unless they are protected by painting or similar. Epoxy is not UV stable.
So it looks like I have to use Resin or Polyurethane.
The stuff is about as useless as breasts > Interesting follow up .... I contacted several major glue manufacturers > ... the fact that has come out is that Epoxy is NOT suitable for > external wood joints, unless they are protected by painting or similar. > Epoxy is not UV stable.
Yes, epoxy is not tolerant of UV; however, if your joints have anything but an edge exposed to UV, you probably have problems other than UV damage to address.
Edge exposure to UV is not going to be a problem.
If you think it will be, then use the "purple stuff" (powder & liquid mixed).
(Have a mental block at the moment and can't think of the proper name for it)
Lew
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