Basic epoxy wood flour questions

Happy New Year!

Please excuse the basic nature of these questions, I am a rank beginner with regards to using epoxy.

First: I have a CLC Toolbox that I would like to epoxy. Do I need to coat all of the pieces prior to assembly or assemble first and then epoxy? 

Second: The epoxy kit purchased with the Toolbox included wood flour. I am not sure what to use the wood flour for? Is this for filling screw holes/gaps when building boats but not needed for the Toolbox? 

Thank you!

Kind regards,

Topher

Sacramento, CA


14 replies:

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RE: Basic epoxy wood flour questions

Hey Topher,

You gotta start somewhere.  While I admittedly have no experience with the new CLC toolboxes, I can only guess without reading the manual. 

I would say yes, it's easier to coat all the pieces with unthickened epoxy first while they're flat on the work bench.  You will probably need to roughen up the mating surfaces before assembly with sandpaper because the epoxy adheres better. 

Another guess is that the wood flour could be for thickening the epoxy that you put in the joints prior to assembly/clamping.  For the boat kits, wood flour is used to produce a fillet that transitions to pieces of wood in the corners, providing a kind of diagonal reinforcement between two pieced of wood that are joined at an angle.  Does that make sense?

If the idea is to thicken the epoxy that you put into the joints just prior to assembly, then we've all decided that slathering unthickened epoxy into the mating parts first, which allows it to soak into the wood fibers, which then in turn bonds to the thickened epoxy in the joint.

Nothing around here is ever easy, but it's always worth the effort...

RE: Basic epoxy wood flour questions

Captain Skully,

Thank you for the input. 

Coating all the pieces while flat seems very appropriate. I assume there is no real increase in the thickness of the piece due to the epoxy as this would make the tabs thicker and the slots thinner, reducing the tolerance of already realatively tight joints. 

Thank you for the explantion of the wood flour being used to diagonally reinforce a joint. Based on your explanation I am going to assume I do not need to use any wood flour with this kit as it is tab and slot and can be used without any expoxy/wood flour at all due to the engineering and fit. 

Thansk, again. 

Topher

RE: Basic epoxy wood flour questions

Woodflour is a thickening agent for epoxy. Unthickened epoxy is pretty viscous, which is great for coating and laminating, but not for gluing. The epoxy will just flow out of the joint, leaving it epoxy-starved and weak. To get around this, we add some kind of thickener, in this case wood flour. It keeps the epoxy from flowing out of the joint. Usually the woodflour is added to the already mixed epoxy to thicken it to the consistency of mayonnaise. You definitely want to use woodflour for gluing.

The other use for woodflour is to make fillets, as mentioned above. There it's thickened to peanut butter consistency.

There's also two uses for precoating. The first is to seal and waterproof the wood. The second is to pre-soak the joints before applying glue for fillets. Wood, especially endgrain, will suck up epoxy like crazy through capillary attraction. Since every other layer of plywood is endgrain, you could end up with a dry joint. So, first paint the joint with unthickened epoxy, then give it a few minutes to soak it up, add more if it looks dry, wait a few more minutes and then apply the epoxy glue mix.

Have fun,

Laszlu

 

 

RE: Basic epoxy wood flour questions

   Hello Laszlu,

Thank you for the explanations, it is much appreciated. The generosity of this forum is apparent. 

Kind regards,

Topher

RE: Basic epoxy wood flour questions

Just as a matter of interest, I've never used wood flour as I don't have a source for it here in SW Turkey. For glue I usually mix silica with epoxy, for fillets I use a mixture of microballoons and silica and for some other applications (usually not boat related) I sometimes use fibreglass microfibres but that is a heavier substance. 

My boats are holding up well.  :)

RE: Basic epoxy wood flour questions

When mixing additives to thicken epoxy for boat building, there are usually two main categories, structural and fairing.  Colloidal silica, Cell-O-Fill, wood flour, microballoons, etc.  all have their place in that spectrum.  Here is a good guide.  I know this is West Systems and CLC distributes MAS, but the information is still applicable and I find very valuable.

https://www.westsystem.com/filler-selection-guide/

There are various other additives like graphite, sand, walnut shells, etc. that have other purposes, which are pretty cool too.

RE: Basic epoxy wood flour questions

 

   I put together one of the tool box kits as a present to my wife.  It's actually to hold all her makeup, hair and other tools of a female persuasion, not chisels and screwdrivers!  And it was her request.  I stained it and varnished it, but didn't use any epoxy.  The kit goes together very tightly, and needs no epoxy to hold together.  The sides and handle are all "keyed" together.  BTW, I put 4 coats of varnish on and I had to go over the tabs and slots to sand the varnish back to get it to go together.  The kit is very closely cut, such that the varnish thickness made many of the slots and tabs not fit.  The thing is to sand all the pieces and slots ahead so you can finish the parts flat and then put it together.

The only thing I glued was the 2 halves of the handle and I just used wood glue for it.  I bought just the kit, directly from CLC at their Annapolis shop, and it didn't come with any epoxy kit, so I'm not sure if you got the kit because you ordered it separately, or you just got one gratis?

RE: Basic epoxy wood flour questions

 

   I use wood flour as a thickener in fiberglassing joints. I used it to join the hull pieces (with fiberglass tape) to join the hull pieces in my Chesapeake 17, as well as the two bulkheads. I used it in my strip-built Guillemot to join the top and bottom (again, with fiberglass tape.) For gluing, especially when the glue might also be a space filler, I use Cab-o-sil.

For the guy who said he didn't have a source of wood flour, I have used the powder that comes out of my random orbital sander. I think it's best when you get the flour by sanding the same species of wood as you will be using it on, with fairly fine sandpaper, but that's mere speculation on my part.

RE: Basic epoxy wood flour questions

 

   I use wood flour as a thickener in fiberglassing joints. I used it to join the hull pieces (with fiberglass tape) to join the hull pieces in my Chesapeake 17, as well as the two bulkheads. I used it in my strip-built Guillemot to join the top and bottom (again, with fiberglass tape.) For gluing, especially when the glue might also be a space filler, I use Cab-o-sil.

For the guy who said he didn't have a source of wood flour, I have used the powder that comes out of my random orbital sander. I think it's best when you get the flour by sanding the same species of wood as you will be using it on, with fairly fine sandpaper, but that's mere speculation on my part.

RE: Basic epoxy wood flour questions

Thank you for all of the input. 

I purchased the epoxy kit so I could venture into the world of epoxy as this is something I have no experience with. I wanted to start with a small build that used expoxy to see if it was something I would enjoy anticipating the option of building a Kaholo SUP. 

With the tight tolerances of the Tool Box kit I am leaning towards assembly then epoxy. 

Topher

RE: Basic epoxy wood flour questions

   Easy to make your own wood flour.  Collect the dust from anything that's makes saw dust.   Put the dust in a flour sifter over a large bowl and sift away.   There's your wood flour.

You can even collect the dust from various woods to color match for later.  I've been saving up Mahogany and Spruce dust for that reason.  Works well.

RE: Basic epoxy wood flour questions

I discovered recently that the wood flour that epoxy company sells is actually food-grade fiber that's an additive to various foods.  Weird, huh?  I will say that while you can add sawdust, even sifted, wood flour is considerably more fine than anything that gets produced in my shop in a quantity that would be useful.  More like the stuff that floats in the sunbeam and gives me a slight case of asthma at the end of a day in the shop.  A tub of wood flour is less than $20.

http://www.lfsmarineoutdoor.com/system-three-wood-flour-2-sizes.html

RE: Basic epoxy wood flour questions

   I think for creating smooth fillets fine powder is great.  There's an argument to be made for longer wood fibers strength wise.  Kind of like using chopped fiber vs glass balloons.  

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