The term 'wicking' has been used on several ocassions when the topic involves epoxy and wood.
The phenomenon exists and I won't argue it's validity. Let's first see if we can define it.
Wicking, as I understand it, is when the epoxy applied to wood is drawn into the cell structure of the wood.
It does this in the exact same manner as if water were applied. It's drawn into and soaks the wood.
The woods that we use are hopefully dry, seasoned and acclimated to their surroundings.
The cell structure is almost collapsed and holding only about 6-12% of it's capacity.
Wood breathes. It draws moisture in when subject to greater humidity than it's current state
and gives up moisture when subjected to dryer surroundings.
Where this condition of wicking is of greatest concern is at the 'A' joint though other areas of the cue are also concern worthy.
The concern is that should wicking occur, the act of too much of the applied epoxy being absorbed,
it would leave the hole without sufficient epoxy to insure adequate bonding of the tenon
to the interior wall of the blind-hole that the tenon is being install into.
This is a legitimate concern as a glue starved 'A' jnt. can result in an annoying 'buzz' or rattle.
Strength of the bond may be suspect as well.
Now for some of my thoughts.
While wicking does occur via the end-grain it may not be to the degree that we think it is.
As to the sidewall, it may be almost non-existent.
When I said that wood breathes, it does the majority of that via the end-grain.
When we want wood to dry slowly, we wax the ends to slow the process.
Un-waxed ends are subject to splitting due to too rapid of an exchange.
In a blind-hole/tenon configuration, such as the 'A' jnt., you have two end-grain surfaces.
Yes, these two surfaces will take their share of epoxy and more but only to an extent.
Imagine an assembly procedure where you have liberally swabbed the hole, 100% coverage and
you've done the same to the screw and tenon. You now start to screw the two parts together.
The first thing that will happen is that you'll start to build internal hydraulic pressure.
You want to be careful here because you'll be building pressure quickly. What else is happening?
The hydraulic pressure is forcing epoxy into the end-grains and those little cells are filling fast.
Did I mention viscosity? Probably a good time to address it.
Water is as thin as, well, water. When wood breathes it's breathing the thinnest water of all, gaseous H2O.
Epoxy has a much stiffer viscosity to begin with but has the added element of pressure behind it.
Hydraulic pressure will force the epoxy into the cells of the wood but they are only going to absorb
so much before they're full and can't absorb anymore yet there is still pressure within the hole.
You need an escape mechanism here or you're going to blow the hole. When you split a F/A, you can hear it across the room.
Some cut grooves & some drill holes. Doesn't matter how you vent but you must vent somehow.
As this venting and equalizing is going on, something interesting is happening with our epoxy; it's starting to cure.
It's by no means a solid yet but from the minute you mixed it, the viscosity has been getting stiffer.
You've got a cell-structure that's full, you've got epoxy getting thicker by the second and hopefully you vented the psi.
Where's the wicking??? My guess would be that in instances where wicking has occurred, there wasn't enough epoxy used.
There are a couple of keys to making this connection a success. Pick the ones you like.
Obviously a good epoxy is paramount. One that starts out thin and gives you time to do your work.
Pace yourself and know your epoxy and it's 'working' time. Try to be consistent in your procedure.
Use cautious diligence in your assembly, let it go together slowly and naturally and don't force it.
Allow the venting to happen, it's suppose to. You're reducing the pressure and allowing the excess epoxy to escape.
There should be just a little 'too much' epoxy escaping. I want to see it exit rather than wonder if I used enough.
Any thoughts, theories or experiences you've had that you'd like to share would be welcomed and appreciated.
Thanx Much, KJ
The phenomenon exists and I won't argue it's validity. Let's first see if we can define it.
Wicking, as I understand it, is when the epoxy applied to wood is drawn into the cell structure of the wood.
It does this in the exact same manner as if water were applied. It's drawn into and soaks the wood.
The woods that we use are hopefully dry, seasoned and acclimated to their surroundings.
The cell structure is almost collapsed and holding only about 6-12% of it's capacity.
Wood breathes. It draws moisture in when subject to greater humidity than it's current state
and gives up moisture when subjected to dryer surroundings.
Where this condition of wicking is of greatest concern is at the 'A' joint though other areas of the cue are also concern worthy.
The concern is that should wicking occur, the act of too much of the applied epoxy being absorbed,
it would leave the hole without sufficient epoxy to insure adequate bonding of the tenon
to the interior wall of the blind-hole that the tenon is being install into.
This is a legitimate concern as a glue starved 'A' jnt. can result in an annoying 'buzz' or rattle.
Strength of the bond may be suspect as well.
Now for some of my thoughts.
While wicking does occur via the end-grain it may not be to the degree that we think it is.
As to the sidewall, it may be almost non-existent.
When I said that wood breathes, it does the majority of that via the end-grain.
When we want wood to dry slowly, we wax the ends to slow the process.
Un-waxed ends are subject to splitting due to too rapid of an exchange.
In a blind-hole/tenon configuration, such as the 'A' jnt., you have two end-grain surfaces.
Yes, these two surfaces will take their share of epoxy and more but only to an extent.
Imagine an assembly procedure where you have liberally swabbed the hole, 100% coverage and
you've done the same to the screw and tenon. You now start to screw the two parts together.
The first thing that will happen is that you'll start to build internal hydraulic pressure.
You want to be careful here because you'll be building pressure quickly. What else is happening?
The hydraulic pressure is forcing epoxy into the end-grains and those little cells are filling fast.
Did I mention viscosity? Probably a good time to address it.
Water is as thin as, well, water. When wood breathes it's breathing the thinnest water of all, gaseous H2O.
Epoxy has a much stiffer viscosity to begin with but has the added element of pressure behind it.
Hydraulic pressure will force the epoxy into the cells of the wood but they are only going to absorb
so much before they're full and can't absorb anymore yet there is still pressure within the hole.
You need an escape mechanism here or you're going to blow the hole. When you split a F/A, you can hear it across the room.
Some cut grooves & some drill holes. Doesn't matter how you vent but you must vent somehow.
As this venting and equalizing is going on, something interesting is happening with our epoxy; it's starting to cure.
It's by no means a solid yet but from the minute you mixed it, the viscosity has been getting stiffer.
You've got a cell-structure that's full, you've got epoxy getting thicker by the second and hopefully you vented the psi.
Where's the wicking??? My guess would be that in instances where wicking has occurred, there wasn't enough epoxy used.
There are a couple of keys to making this connection a success. Pick the ones you like.
Obviously a good epoxy is paramount. One that starts out thin and gives you time to do your work.
Pace yourself and know your epoxy and it's 'working' time. Try to be consistent in your procedure.
Use cautious diligence in your assembly, let it go together slowly and naturally and don't force it.
Allow the venting to happen, it's suppose to. You're reducing the pressure and allowing the excess epoxy to escape.
There should be just a little 'too much' epoxy escaping. I want to see it exit rather than wonder if I used enough.
Any thoughts, theories or experiences you've had that you'd like to share would be welcomed and appreciated.
Thanx Much, KJ
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