My company primarily makes large slab tables with lots of live edge, defects, holes, etc. We currently use West Systems epoxy for our pours. We typically for very large voids, do three pours. The first establishes a base coat, the second we mix the epoxy with coffee grounds as a filler, and the final top coat. Has anyone else used fillers like coffee? Colloidal silica? Etc?
Most of our large voids are filled with black colored epoxy, so I was wondering has anyone ever drilled holes on inner edges to give the epoxy something to grab to keep it more stable?
I have used wood flour made with my floor edger using 100 grit paper. I mix enough dust to make a paste like peanut butter to fill holes as large as a ¾ inch pipe in one go. The dust will darken so it matches a knot color from the same species. More dust in the mix will take stain better when finishing. I have never used black color in the mix. On a larger pour I use wax paper or plastic film to keep it from dropping out.
Yes, I use colloidal silica in almost every mix I use even for adhesive purpose. If I'm using it to fill a small void, I mix using silica to about catsup thickness before adding wood dust from my sander bag to get the color darker.
However, large epoxy fills are not flexible enough to move with seasonal changes, so on larger patches, I may use a router to square up the sides of a irregular void, the stick a wide piece of masking tape over, which I then do a rubbing to mark the edges that I bandsaw a plug from a scrap. When you use thick colored epoxy to glue it in, that colored epoxy line just becomes a growth ring, and the wood plug will move with the seasons too.
Abatron make a filler that they claim is flexible, but I haven't tried it, so can't give any endorsement.
If I had to put that much effort into a really large void, I'd use some router templates and inlay a piece of wood. I use dried, used coffee grounds for the small voids in artist turnings. Black epoxy looks too much like plastic, I much prefer the organic look of the coffee and it is dark enough to look like a knot from across the room.
Coffee grounds. Where and when did that idea come from.
The coffee is certainly not a clean neutral material to mix with the epoxy. Its full of acid and a bunch of unknown chemicals.
If you use West System, then you should know their whole product line. They've got silica, cotton fibers, wood flour, etc.
Silica is added to almost every filler to control viscosity of the resin.
Aren't you a wood shop? If you want to step off the reservation and make your own mix. Why not use really fine saw dust?
Drill holes. Not necessary unless the wood is dry rotted. Rough up the surface with 60-80 grit and go for it.
You can apply more coats without sanding if you do it within the "green" window. You get true chemical bonding when the epoxy is still rubbery to feel. You have to sand it once again with 80 grit once it has cured.
I would call West System and talk to their techs. They have excellent customer service.
I've been using used and dried coffee grounds for decades. For me, the benefit is some random coloring and particle size in the mix. Fillers give too uniform of look. I want something with a little more organic look compared to other even colored fillers.
I have an image of rich c needing a large patch for a rustic table top, and running 5-6 pots of coffee thru the shop coffee pot to get enough grounds. Rich is over there by the table - eyes wide open and bloodshot, caffeine coursing thru his veins, and he is just vibrating in place, teeth grinding.
But there are enough coffee grounds to fit the gap.
Interesting image David. Pulling out what hair I have left on my head? Naw! I'm not in the style of taking these cracked and nearly firewood grade slabs, and making tables of them. I'm more of a 4-way mahogany crotch match, or birds eye maple kind of guy. Now with my artistic turning, I don't throw away a huge maple bowl because a knot starts to go from solid to punky in the final couple cuts. That's where the fill comes in. Just completed a little fill on a cremation urn. Lots of labor hollowing out a big vessel, so a few coffee grounds in the bark inclusion worked out perfectly.
A nearby business makes pen blanks for wholesale. He does thousands of them a month.
I was there one time and he showed me the coffee beans in a white glue matrix they were selling as pen blanks. They bought all sort of shorts and rips form all over the world, and ripped and cutoff for pen blanks.
The coffee pen blanks were whole beans, not grounds. They did have a slight aroma. Might make for a good tasting pen if you chewed on it bit.
One shop I worked in required the coffee grounds be spread out under the Dogwood tree by the back door. This was one tremendous Dogwood that flowered like no other. The owner swore it was the coffee grounds.
I've turned the coffee and cream blanks. Smell wonderful when turned, and I tell customers to hit it with a little 600 grit to remove the oxidation from the beans to get the smell back. A casting resin is used, it's not a glue matrix. A skew chisel is the best tool because a scraper will actually pic out some beans. The skew shears off the chips. Most castings are made with Alumilite urethane because it does not have the shrinkage that polyester resin does. Incredibly short pot life so not great for big pours. The person doing the casting has to weight down the beans so they do not all float up and slightly out of the resin. Most use hardware cloth and a piece of steel bar to hold them down. Usually poured and then placed in a pressure pot to reduce air bubbles. An infinite number of things have been cast for pen blanks. Pepper corns, cherry pits, tiny pine cones, gum tree seed pods, aluminum or brass machining waste, key machine brass dust, aluminum honey comb, glitter, and the favorite is called "worthless wood". Usually this is scrap trimmings of burl, cast into resin. Funniest one I saw was a guy that cast cat turds in resin. He won the ugly pen contest one year with that! I've made a lot of pens from corn cobs. You have to find the right size of cob so the brass inner tube fits into the soft center. I saturate the cob with thin CA glue and it turns about like soft maple. Really popular with the neighbors near the farm where I grew up. Bill, I use the grounds straight from the filter. They have to be bone dry though, epoxy doesn't like water. I just spread them out in the sun for a day, and ready to go!
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