JohnS
Well-Known Member
For any interested here is a question I send to the manufacturer of Aerodux and the answer I got. I was interested to see just how strict the no gap and high clamp guidelines are. Seems a bit more friendly then I thought.
I purchases Aerodux 185 in the US with the intention of using it to build a small plane. I've chosen Aerodux rather than epoxy resin because I, frankly, feel that it's ease of use is its most attractive advantage. I've used it to build boats and have seen it behave poorly in the heat. It also irritates my skin.
In any case I'm writing to you to discuss the subject of gap filling and clamping pressure. The conventional wisdom says recorsinols have to be clamped tightly. My question is why. Is it to facilitate penetration or merely to minimize gaps size. I'm curious to know if I apply moderate clamping pressure to a well fit joint will I achieve a solid bond as long as I have a gap of say .5 mm or less. Recorsinols has a reputation of being hard to use and unforgiving. If it has made some improvements that make it a bit more forgiving I'd like take them into consider. I want to understand better how it works rather than being scared of it.
For instance I need to join a perfectly machined 1x1 piece of spruce to 1/8" spruce plywood. So if both surfaces are perfectly flat will stout clamping pressure and positive contact suffice or do I need in the order of 75psi.
Hopefully I'm making clear where my concerns lie. I know its a very capable product. I just want to get some sound advice to counter some of the bad things the epoxy zealots have to say.
Answer
Hello John,
Sorry for the late reply. Summer vacation!
Thank you for your interest and questions. Always nice with people digging a little more into the theory before using the adhesive uncritically.
Aerodux 185 is a condensation adhesive, and condensations adhesives tends to create a more brittle glue line. This is not a problem if you keep to a relatively thin glue line. With thicker glue lines you can sometimes observe small cracks after curing. Approximately 30% of the adhesive solution is water, and this water needs to be able to penetrate into the wood or to the surroundings during curing. If you have a too thick glue line, water will be “trapped” and a moisture gradient will be created. The internal forces will be high and might finally result in cracks.
Because of this we do not recommend more than 1mm glue line thickness. Thinner glue lines will be stronger and better. Optimal glue line thickness should be in the area of 0,1-0,2 mm.
But, the glue is tested and approved for the gluing of load bearing constructions with up to 1,0mm.
There are several reason for using some pressure:
• bring the surfaces to be bonded in contact
• overcome the viscosity of the adhesive
• overcome the internal swelling pressure
• overcome surface imperfections
• obtain adhesive penetration
• hold the assembly until the adhesive has set
The above reasons are more relevant when producing bigger load bearing constructions.
In your case, as you have described it below, it would most probably be ok with close to no pressure. I would anyway recommend some pressure applied by hand clamps. But yes, you can forget the 75psi requirement.
One advice though: always use as short open assembly time as possible, but make sure to use at least 15-20 min closed assembly time, before you apply the hand pressure.
I purchases Aerodux 185 in the US with the intention of using it to build a small plane. I've chosen Aerodux rather than epoxy resin because I, frankly, feel that it's ease of use is its most attractive advantage. I've used it to build boats and have seen it behave poorly in the heat. It also irritates my skin.
In any case I'm writing to you to discuss the subject of gap filling and clamping pressure. The conventional wisdom says recorsinols have to be clamped tightly. My question is why. Is it to facilitate penetration or merely to minimize gaps size. I'm curious to know if I apply moderate clamping pressure to a well fit joint will I achieve a solid bond as long as I have a gap of say .5 mm or less. Recorsinols has a reputation of being hard to use and unforgiving. If it has made some improvements that make it a bit more forgiving I'd like take them into consider. I want to understand better how it works rather than being scared of it.
For instance I need to join a perfectly machined 1x1 piece of spruce to 1/8" spruce plywood. So if both surfaces are perfectly flat will stout clamping pressure and positive contact suffice or do I need in the order of 75psi.
Hopefully I'm making clear where my concerns lie. I know its a very capable product. I just want to get some sound advice to counter some of the bad things the epoxy zealots have to say.
Answer
Hello John,
Sorry for the late reply. Summer vacation!
Thank you for your interest and questions. Always nice with people digging a little more into the theory before using the adhesive uncritically.
Aerodux 185 is a condensation adhesive, and condensations adhesives tends to create a more brittle glue line. This is not a problem if you keep to a relatively thin glue line. With thicker glue lines you can sometimes observe small cracks after curing. Approximately 30% of the adhesive solution is water, and this water needs to be able to penetrate into the wood or to the surroundings during curing. If you have a too thick glue line, water will be “trapped” and a moisture gradient will be created. The internal forces will be high and might finally result in cracks.
Because of this we do not recommend more than 1mm glue line thickness. Thinner glue lines will be stronger and better. Optimal glue line thickness should be in the area of 0,1-0,2 mm.
But, the glue is tested and approved for the gluing of load bearing constructions with up to 1,0mm.
There are several reason for using some pressure:
• bring the surfaces to be bonded in contact
• overcome the viscosity of the adhesive
• overcome the internal swelling pressure
• overcome surface imperfections
• obtain adhesive penetration
• hold the assembly until the adhesive has set
The above reasons are more relevant when producing bigger load bearing constructions.
In your case, as you have described it below, it would most probably be ok with close to no pressure. I would anyway recommend some pressure applied by hand clamps. But yes, you can forget the 75psi requirement.
One advice though: always use as short open assembly time as possible, but make sure to use at least 15-20 min closed assembly time, before you apply the hand pressure.
