Filling cracks and knot holes in wood floor

[thechknhwk]

What would be the best way to fill knots like these in my hard wood floor?  I want something black and sandable, and sort of flexible, so it don't crack out when the floor inevitably moves.  I also have some seam gaps to fill in, mostly on the butt joints.  I checked into the west system epoxy, but the fella helping me said it's like water when it's poured and could use a lot of epoxy if it goes through the knot and under the hardwood floor to the subfloor and keeps running out.  A local shop has some hardwood floor filler, but it was in red oak tone.  Anyways suggestions appreciated.

[low_48]

My favorite filler for gap problems in my woodturning, is used and dried coffee grounds mixed into epoxy. It has some color differences in it so it doesn't look as much as plastic, like using dye in epoxy does. You can add filler to epoxy to thicken it. I wonder about packing something in the bottom or the holes to keep the epoxy from flowing out. Black paintable caulk? I'd call West back and ask them about fillers and a compatible damning material for the bottom of the holes. Durham's rock hard putty is an old staple of mine, but don't know about making it dark for the knots. Checked their website, CAN I TINT IT BEFORE PATCHING HOLES?
Yes. Durham's can be colored by adding a water-based coloring agent to the putty when mixed. Use black to create gray colors. Use a dry powder pigment that you might find at an art supply store.

[Savannahdan]

Like low48, I use coffee grounds (used and dried) for a dark filler.  You could consider filling in the hole about half way with grounds and super glue to hold them in and then adding coffee ground/epoxy to finish filling the holes.  Be careful with the super glue and it's toxic fumes. I'm not sure I'd use the coffee ground/super glue mixture where it would be exposed to folks walking on it.  I also use copier/printer toner with super glue for some of my projects.  It's nasty to handle but looks great on the finished product.

[thechknhwk]

I was thinking black silicone in the holes with epoxy over top of it.  I wonder about putting the silicone in the seam cracks though, if it would be ok to finish over top of it.  Thanks for the ideas

[mesquite buckeye]

My eucalyptus floor was full of holes, lots of them bigger than yours. As long as the floor is tight to the subfloor the system 3 epoxy will work fine. That's what I used. If the holes are big, especially on the bottom, you may have to put it on 2 or 3 times. Good news is that each time takes less. The epoxy also strengthens the weak parts of the floor. ;D

[thechknhwk]

My eucalyptus floor was full of holes, lots of them bigger than yours. As long as the floor is tight to the subfloor the system 3 epoxy will work fine. That's what I used. If the holes are big, especially on the bottom, you may have to put it on 2 or 3 times. Good news is that each time takes less. The epoxy also strengthens the weak parts of the floor. ;D

That's one of the things I'm concerned about.  I do have some bridging going on.  I have pieces from 2 to 8' long.

[Kbeitz]

I mix dark stain and sawdust... I let it dry and then mix with glue and shovel it in....

[Kasba]

I use ca glue with coffee grounds or wood dust. Please be careful with some of the copier toners as they are very carcinogenic.

[Czech_Made]

I always used just sawdust and wood glue, coffee grounds sound interesting.

[69bronco]

The guy you talked to about West system didn't give you much info apparently. They have a host of thickening and fairing products . You can go from water consistency to the point you'll need a putty knife to work it. There is also graphite powder available used on boat bottoms, you mix with epoxy. It is black, reasonable and simple to use.

[ozarkgem]

I used fiberglass resin and black paint color. then sanded the whole floor down. I had some pretty big knot holes.

[scsmith42]

I was thinking black silicone in the holes with epoxy over top of it.  I wonder about putting the silicone in the seam cracks though, if it would be ok to finish over top of it.  Thanks for the ideas

Generally finish will not adhere to black silicone, so I'd stay away from it.

I've made my own filler by using fine sawdust and finish.  I like the ideas from others about using coffee grounds for the dark color. 

There are epoxy sticks available from woodworking shops that you can use to plug the holes.  I've been very pleased by them but would not want to do a huge volume with them.  They are great for pin and worm holes though.

Re the bridging, the trick here is to use a "5 minute" epoxy to fill in the bottom of the void and get things sealed up.  After it has cured then go back with a West System or Aero Marine epoxy to fill up the rest of the void.  It's best not to do more than 1/4" of filling at a time.  Air bubbles can be removed by heating with a hair dryer or heat gun right after you pour the epoxy. 

Epoxy can be colored with artist oil paint or black ink.  I've even used black car paint to color it.  Artist oil paint can take a while to dry.

[thechknhwk]

I put black silicone in the bottoms of the holes, not filling them up all the way.  Some of them plugged, and some of them kept sucking down the epoxy, so we started mixing it with walnut sawdust.  It will need another application though without the sawdust.