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How to Stop Black Epoxy from Wicking into Wood Fibers2/1
All, need some advice on using black epoxy as a contrasting color fill in wood. I have a fairly intricate logo CNC routed into a hardwood display (happens to be a mix of birch and walnut). My plan was to fill it with System Three epoxy tinted black before sanding flush. However, the epoxy is so thin it's wicking into the end grain wood fibers around the perimeter of the routed recesses. Ends up looking like hundreds of black "roots" growing into the wood.
Got any ideas on how to achieve this look without the wicking?
When using epoxy as a glue, common practice is to wet the joints with unthickened epoxy before thickening the mix with silica powder and reapplying, so as to get good penetration. Stands to reason that if you try thickening your black mix, you might not get as much wicking action.
Apply a thin coat of clear epoxy and let it cure. Sand/wash if required for second application and then apply your black epoxy and it should not wick.
Reduce the epoxy by 25% with rubbing alcohol. You can buy 91% at most drug stores. It is by far the best solvent/reducer for epoxy resins.
Use the reduced clear epoxy as a sealer as Leo suggested. One quick coat let it cure overnight.
The other option is to seal the entire piece with shellac Sealcoat. then do the black epoxy.
Are you using the West system graphite powder?
Thanks for the tips so far. I have just about decided to re-do the logos and then use a tiny brush and paint to match the original colors supplied by the customer before we decided to go with black. I'm a little worried about trying the clear epoxy to pre-seal the end grain around the recesses because many of the details are milled with a 1/32" OD bit, the smallest I feel comfortable running in my CNC. However, Adam's tip above to first thin the resin with alcohol might be worth a shot. Just can't have the clear epoxy fill up the grooves and leave no room for the black epoxy to create the design later...decisions, decisions.
I'm attaching a picture of the original result--keep in mind this portion of what I'm cutting fits in a box about 1" high by 5" wide and a 1/32" end mill barely fits inside the bottom row of text.
Does it have to be epoxy, why not paint and then sand and then clear?
Leo, you're thinking what I'm thinking. Would have been nice having it full flush, but inset's probably OK, too. By the way, attached is what the two logos really want to look like when done. Both are roughly 5" wide when done (goes on employee award plaques)
I think pre sealing with the full strength epoxy is fine. You just need to get it out of there.
Put a pc of tape over the area that you are cutting.
Then cut the area.
Then brush the clear epoxy into the the area.
Then let it sit for 10 minutes or so so it can wick into the areas you don't want the black to go.
Then blow out the area with air and wipe down.
After it cures pore the black epoxy into the area and just let it overfill by a bit.
After it cures sand it down to remove the tape (if you can't just pull it off).
Maybe try routing through a mask, paint the recesses, then fill with clear epoxy or casting resin. I think you will see about the same result as you will be looking through the clear into the paint.
Avoid using alcohol or other product that has low surface tension, as such liquids will penetrate the wood more easily. The double epoxy coating gets my vote.
I ended up using shellac due to the narrowness of the routed grooves in many areas. I was concerned that getting the clear epoxy in there, and then out again before it cured, would be tough. If any had remained inside the grooves, I would likely have wound up with fuzzy line edges once the black was poured in.
The shellac worked out fairly well as you can see in the attached finished product photos.
Black Epoxy glue takes at least 1hr for setting and curing. It is enough time for the liquid glue spreading out and causes wicking, give "root" look on the CNC wood word.
You can use clear polyurethane for sealing the wood, then sanding when after CNC and before applying the black polyurethane coat on.
It will faster but last long under UV and moisture than shellac.