Sawdust in Epoxy

[Bernie Kopfer]

I will be using epoxy to bond a metal garden trowel into a wood handle. The hole is 1\16th of an inch larger than the diameter of the metal due to tangs on the metal shaft. Does adding sawdust to the epoxy make it stronger? I know that sometimes fibers are added to concrete to make it more flexible and stronger and I wonder if the same applies with epoxy and sawdust. I can't find any research on the subject and wonder if any of the members here have some antedotal experience one way or the other. Thank you for your help.

[carl zietz]

I would not think it is necessary. I just did a loose fit wood handle on a metal tang display dagger, used devcon 2 ton epoxy, and it is solid as a rock.

[Richard Coers]

Epoxy loves a gap much better than a tight joint. Fillers are used in epoxy to change the viscosity, but not about strength.

[Todd Burch]

Not sure I agree 100% with Richard.

See this filler chart (not sure what system you are using however):

http://www.westsystem.com/ss/filler-selection-guide/


or this product selection chart:

http://www.westsystem.com/ss/product-selection-chart

[Mike Henderson]

I've had good results with epoxy filling gaps and being strong enough to do the job. The worse is that it comes out and you then try something else.

An alternate approach might be to epoxy something wrapped around the tang, then gluing that into the handle.

Mike

[Prashun Patel]

If it were me, I would put solid wood wedges in the hole between the walls and the shaft and then epoxy.
Sawdust won't strengthen the epoxy; it'll leave you with particleboard. Sawdust compresses, so my intuition (not science here) tells me it won't resist the torque as much as would solid wood wedges. The epoxy is there then just to hold everything in place.

[Kyle Iwamoto]

For something like a garden trowel, I would not worry too much about strength. Ive used masking/painters tape to take up the gap, to get a snug fit, and used epoxy liberally to fill that gap. I think at a minimum, the epoxy will hold the tape in place enough so nothing will slide around. the gap filling bonding is a bonus.

[Bernie Kopfer]

Thanks everyone, and thank you Todd for the West System link. It does appear that the use of certain fillers enhances the bond and strength. I'll try to remember to give them a call and see if they have anything to say about sawdust.

[John Coloccia]

If you really want it to never come out, drill some holes tang. When you stick it in the handle, the epoxy will pin the handle in place and will likely outlast you. I would just fill with epoxy and shove in the drilled tang.

[Howard Acheson]

>>>> Does adding sawdust to the epoxy make it stronger?

No. It just makes it thicker in viscosity. Epoxy in and of itself is stronger than wood so wood sawdust would not add any strength. At some point, it would make for a weaker adhesive.

[Bryan Wiesendahl]

I've used sawdust as a filler in polyester resin as a void filler/fairer. Fiberglass places will sell you "wood flour" which is essentially the really fine particles you find in your dust collector, if it separates out the big chunks. The filler acts as a balancer between the epoxy being brittle, the filler being compressible, the epoxy being heavy, the filler being light, etc etc.

Honestly, it's a trowel, and any epoxy based thing will work. If you cut a groove/grooves in the tang then you'll create a larger "keyed" mechanical bond as opposed to the tiny mechanical bond that the roughed up surfaces provide.

[Bryan Wiesendahl]

>>>> Does adding sawdust to the epoxy make it stronger?

No. It just makes it thicker in viscosity. Epoxy in and of itself is stronger than wood so wood sawdust would not add any strength. At some point, it would make for a weaker adhesive.

Not as simple as that, as "strong" is a pretty loose term. The epoxy is definitely harder, but it cracks easily due to brittleness, and has a problem with flexing loads. There's a reason resins are used in conjunction with other materials (filler, fabric, fibers, etc) to provide a composite that has more desirable properties than just one of the materials alone. A 1/8 sheet of pure cured epoxy is easily breakable by hand and a section of fiberglass is easily torn by hand, but put the two together and you get a panel that you can jump on, albeit a bouncily, all day long.

At a smaller level the wood fibers actually act like fiberglass in that the fibers tie the epoxy together and prevent cracks and fissures from propagating along the path of least resistance. You're right that at some point it becomes weaker than just epoxy.

Then again, it is just a trowel, and almost anything will git'er'done.

[Jacob Reverb]

Epoxy loves a gap much better than a tight joint. Fillers are used in epoxy to change the viscosity, but not about strength.

Having used various resins and fillers for many years in marine fab and repair, I agree with Richard's first statement but disagree with his second.

There are several fillers (West System 404 is a good example) that increase the tensile adhesion and compressive strength of epoxies.

But they're probably not necessary for gluing a trowel blade into a handle!

[Alan Lightstone]

There are several fillers (West System 404 is a good example) that increase the tensile adhesion and compressive strength of epoxies.

But they're probably not necessary for gluing a trowel blade into a handle!

I agree with Jacob. I've used a variety of fillers with epoxy to enhance strength (carbon fiber fillings are a favorite), and the joints come out rock solid. I'd just follow West Systems charts and have at it. For this particular application, should work quite well.