Mixing Glues
#1
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Mixing Glues
I just received my Four Star 60 in the mail today and after going through the instructions, I found in the 'more ideas on using CA glue" section a warning against tacking parts together with CA and then going back over the joints with epoxy or waterbased glues because the adhesives will interfere with each other. I have heard of people doing this before, but that have not said anything bad about it. Should I mix glues when building?
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RE: Mixing Glues
I totally agree that you would never want to do things that way. Never mind the mixing of the glues. It's the procedure about tacking things and then going back over them with some other glue. This would imply that the second glue would be dobbed onto the outside of the joint and through some miracle of positive thinking the glue would migrate into the joint....... Ain't gonna happen.
Good woodworking practices always put the glue IN the joint and not dobbed over it. Good woodworking practices also make the glue joints at tight as practical so the glue is there to join the fibers of the wood together at the surfaces in an interlocking patter and not act as a filler. This applies to carpenter's glues as well as all types of CA. The ONLY notable exception to this being epoxy that polymerizes into a plastic and should have a glue line somewhere between the thickness of tissue and printer paper. And I think the new polyurethane glues also require a close fit but no clamping to retain some of the glue as a line. The rest all benifit from light to moderate clamping to keep the joints as tight as practical without damaging things. The term Gap FIlling on the thick CA bottles always makes me shudder when I see folks that think they can get away with poor fits and just use a bit more glue. It's expensive, heavier and weaker than a proper fitting joint. They don't all have to be perfect enough that the fibers bond through molecular cohesion but it's alway good to aim for fits that close enough that you can't fit more than a thickness or two of printer paper into the gap.
Now I'm no angel. I've been known to fill a little hole or crack or other problem with some dust and glue but I give myself a mental boot in the rear when I do. Or I'm using it as a fast filler material in very small amounts to fill in a gap. I definetley don't do this where significant structural loads will be at work.
So it's right as far as it goes and hopefully the idea they set out about smearing glue over an already tacked joint will not become too prevalent thanks to that pamphlet.
Cheers and happy building with your Four Star.
Good woodworking practices always put the glue IN the joint and not dobbed over it. Good woodworking practices also make the glue joints at tight as practical so the glue is there to join the fibers of the wood together at the surfaces in an interlocking patter and not act as a filler. This applies to carpenter's glues as well as all types of CA. The ONLY notable exception to this being epoxy that polymerizes into a plastic and should have a glue line somewhere between the thickness of tissue and printer paper. And I think the new polyurethane glues also require a close fit but no clamping to retain some of the glue as a line. The rest all benifit from light to moderate clamping to keep the joints as tight as practical without damaging things. The term Gap FIlling on the thick CA bottles always makes me shudder when I see folks that think they can get away with poor fits and just use a bit more glue. It's expensive, heavier and weaker than a proper fitting joint. They don't all have to be perfect enough that the fibers bond through molecular cohesion but it's alway good to aim for fits that close enough that you can't fit more than a thickness or two of printer paper into the gap.
Now I'm no angel. I've been known to fill a little hole or crack or other problem with some dust and glue but I give myself a mental boot in the rear when I do. Or I'm using it as a fast filler material in very small amounts to fill in a gap. I definetley don't do this where significant structural loads will be at work.
So it's right as far as it goes and hopefully the idea they set out about smearing glue over an already tacked joint will not become too prevalent thanks to that pamphlet.
Cheers and happy building with your Four Star.
#3
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RE: Mixing Glues
Bruce makes a good point. The whole purpose of glue/adhesive is to join two pieces of material together. Glue/adhesive itself is usually weak compared to the material you are joining. As the layer of adhesive gets thinner, the joint strength approaches the strength of the materials you are joining.
As far as adhesives interfering with each other... sure... one could have chemical compounds in it that break down the other adhesive. Or it could attack the existing adhesive/material interface. You can use different types of adhesives when building, just don't put them on top of one another, or next to each other.
As far as adhesives interfering with each other... sure... one could have chemical compounds in it that break down the other adhesive. Or it could attack the existing adhesive/material interface. You can use different types of adhesives when building, just don't put them on top of one another, or next to each other.