Mixing sawdust with epoxy

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keith
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Joined: Tue Mar 08, 2005 9:25 pm

Mixing sawdust with epoxy

Post by keith » Thu Mar 24, 2005 9:38 pm

Has anyone had any experience doing this when you run out of filler,does it work the same as store bought thickenersor does it compromise the strength of the epoxy.Thanks

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Glen Smith
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Location: Baie-St-Paul, Quebec, Canada

Post by Glen Smith » Thu Mar 24, 2005 10:12 pm

Sawdust is usually quite coarse and not often used as an additive. Sanding dust (120 grit) is preferable to sawdust. If you want to use it for patching a hull it will stick out like a sore thumb. If you want to thicken a glue it will work but it doesn't add any strength to the mixture. For this purpose you could cut up some fiberglass cloth in very fine pieces ( 1/16" ) and add to the epoxy. This will thicken and add strength.

Tommy
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Post by Tommy » Fri Mar 25, 2005 7:27 pm

I used sanding dust thickened epoxy for filleting. Thats how all my trim is glued on and it has been fine. That is also what I use for laminating paddles. I've also used fine sawdust for epoxying broken chairs, etc. Even used it as a filler for a small repair on my car!

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mtpocket
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Location: Indiana

Post by mtpocket » Fri Mar 25, 2005 8:41 pm

Hey Tommy,

What do you drive, a woody? That's very creative. I have never thought of such a use, but heck why not. It's probably cheaper than having a shop do it.

Rob from Hamilton
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Joined: Fri May 21, 2004 9:09 pm

epoxy around the house

Post by Rob from Hamilton » Sat Mar 26, 2005 10:14 am

My wooden garage door was starting to rot, and fall apart, and I fixed it with epoxy thickened with sanding dust. My son is constantly finding uses for my epoxy. One day I saw him and a few neighbour kids out on our front lawn, looking for four leaf clovers. Next thing I know is all these kids are wearing medallions my son made from my (unthickened) canoe epoxy! What does he care? He doesn't pay for it!

As for thickening agents, I use sanding dust, but when I started my first canoe I didn't have any sanding dust so I used regular flour from the kitchen. It worked just fine. It's a little white, but when you mix a little sanding dust in with it, it's okay.

Glen, does finely cut ( 1/16") fibreglass actually add strength? I would have thought longer strands, like about 1/2", would be necessary to add strength. Epoxy is very strong when thickened anyway. In your opinion, when would you need to add strength to epoxy?

Rob from Hamilton

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Glen Smith
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Post by Glen Smith » Sat Mar 26, 2005 10:37 am

West System sells "Microfibers" which I believe are very finely chopped particles of fiberglass cloth to make a stronger bond. Their wisdom is "the harder the materials being bonded, the stronger the bond must be". I believe silica is the second strongest.

Excerpt from West Systems website:

"ADHESIVE FILLERS

403 Microfibers
403 Microfibers, a fine fiber blend, is used as a thickening additive with resin/hardener to create a multi-purpose adhesive, especially for bonding wood. Epoxy thickened with microfibers has good gap-filling qualities while retaining excellent wetting/penetrating capability. Color: off-white.

404 High-Density Filler
404 High-Density filler is a thickening additive developed for maximum physical properties in hardware bonding where high-cyclic loads are anticipated. It can also be used for filleting and gap filling where maximum strength is necessary. Color: off-white.

405 Filleting Blend
This strong, wood-toned filler is good for use in glue joints and fillets on naturally finished wood. It mixes easily with epoxy and lets you create fillets that are smooth and require little sanding. Its color is a consistent brown, so 405 can be used to modify the shade of other WEST SYSTEM fillers.

406 Colloidal Silica
406 Colloidal Silica is a thickening additive used to control the viscosity of the epoxy and prevent epoxy runoff in vertical and overhead joints. 406 is a very strong filler that creates a smooth mixture, ideal for general bonding and filleting. It is also our most versatile filler. Often used in combination with other fillers, it can be used to improve the improve strength, abrasion resistance, and consistency of fairing compounds, resulting in a tougher, smoother surface. Color: off-white. "

Filler selection guide:
ADHESIVE FILLERS

403 Microfibers
403 Microfibers, a fine fiber blend, is used as a thickening additive with resin/hardener to create a multi-purpose adhesive, especially for bonding wood. Epoxy thickened with microfibers has good gap-filling qualities while retaining excellent wetting/penetrating capability. Color: off-white.

404 High-Density Filler
404 High-Density filler is a thickening additive developed for maximum physical properties in hardware bonding where high-cyclic loads are anticipated. It can also be used for filleting and gap filling where maximum strength is necessary. Color: off-white.

405 Filleting Blend
This strong, wood-toned filler is good for use in glue joints and fillets on naturally finished wood. It mixes easily with epoxy and lets you create fillets that are smooth and require little sanding. Its color is a consistent brown, so 405 can be used to modify the shade of other WEST SYSTEM fillers.

406 Colloidal Silica
406 Colloidal Silica is a thickening additive used to control the viscosity of the epoxy and prevent epoxy runoff in vertical and overhead joints. 406 is a very strong filler that creates a smooth mixture, ideal for general bonding and filleting. It is also our most versatile filler. Often used in combination with other fillers, it can be used to improve the improve strength, abrasion resistance, and consistency of fairing compounds, resulting in a tougher, smoother surface. Color: off-white.

Tommy
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Post by Tommy » Sat Mar 26, 2005 2:10 pm

Depends on what you mean by "strong".

It is my understanding that colodial silica makes a "harder" finish for, as they say, abrasion resistance. They are like little glass beads. That is why I mixed it in with my graphite/epoxy for the bottom of my canoe.

But for a "strong" bond when glueing two items together then I would suspect fibres would be better but not as hard as the silica.

Correct me if I'm wrong.

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Glen Smith
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Location: Baie-St-Paul, Quebec, Canada

Post by Glen Smith » Sat Mar 26, 2005 2:25 pm

That sounds right Tommy. All the information I have read paints that picture.

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Erich
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Location: Sault Ste Marie, Ontario

Post by Erich » Sun Mar 27, 2005 10:20 am

An item used a lot is my shop is pine dust. I feed a small white pine board into my 6 x 48 inch 50 grit belt sanding machine. This is atttached to a cleaned vaccum. I usually grind up about a gallon of sawdust and sift it thru a fine screen to remove the lumps. White pine mixed with epoxy will turn a nice carmel colour and will fill in any voids on a hull. I work with white cedar and this mixture will look like wood grain when hardened and sanded. It is almost invisible after the hull is covered with glass. To make other colours I add whatever is around such as walnut, rosewood, purpleheart or anything that will add a different shade to the mixture.

I like to use cotton fiber for laminations. This mixed with epoxy gives a strong bond between laminations. Coat all surfaces with straight epoxy and then add a cotton/epoxy mixture on one side. Clamp as normal. This mixture sands very nicely.
So much water. So little time.

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