Filling large knot holes and voids

jpaul

New User
John
Hello all, first real question post here.
I'm about to start working on a coffee and end tables project from white oak that is still rough cut right now. There are some knot holes and voids and such in it that will need filling. I'm thinking of using bondo if I can find a dark/black color instead of the usual red or gray. Is there a way to tint it? Is there something better/cheaper?
Thanks.
 

jcz

Johnny
Corporate Member
Get some CA glue and fill with sawdust if you want it to blend in. Or if you want a contrasting color use coffee grounds or brass shavings or turquoise. The sky is the limit. Medium ca is what I use.
 

pop-pop

Man with many vises
User
Hello all, first real question post here.
I'm about to start working on a coffee and end tables project from white oak that is still rough cut right now. There are some knot holes and voids and such in it that will need filling. I'm thinking of using bondo if I can find a dark/black color instead of the usual red or gray. Is there a way to tint it? Is there something better/cheaper?
Thanks.
The first thing that comes to mind are Mohawk Epoxy Sticks which come in many colors. Just knead and press into the void.
 

jpaul

New User
John
Thanks for the quick reply guys.
I just put down hickory flooring throughout the house and I think a dark color filler would look good for a contrast against the oak.
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
For "large" knot holes I would definitely recommend epoxy. You can tint it to whatever color you want. Coffee grounds work well for dark knots. I prefer to just use black dye, but I used to use coffee grounds.
 

Bas

Recovering tool addict
Bas
Corporate Member
For "large" knot holes I would definitely recommend epoxy. You can tint it to whatever color you want. Coffee grounds work well for dark knots. I prefer to just use black dye, but I used to use coffee grounds.
This. Coffee grounds does two things, it provides a dark color, and it acts as a filler. You can also use epoxy, some fine sawdust, and a couple of drops of dye (like Transtint). I like adding some sawdust/ filler to make the epoxy dry harder/ feel less flexible.

Cocoa powder works well for Cherry BTW - good color match.
 

CrealBilly

Jeff
Senior User
I like to use thin CA to "stabilize" the knot, it wicks into the smallest crack, even the ones you can't see. Then a little fine sawdust from the sander, followed by more thin CA glue. Then fill it with thick CA or quick dry 2 part clear epoxy. Once dry sand flush.

Bas and others have some good advise about using "other stuff" that is more creative than my simple quick sawdust approach. I usually just grab a little sawdust out of the sander and throw it at the defect and squirt it with thin CA, so it's quick.
 
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zdorsch

Zach
Senior User
Epoxy works well and can be dyed. I use it frequently when filling knot holes. I’ve found CA better for smaller holes.

Ive found the big box store stuff doesn’t work as well as System 3 or West systems. The five minute system 3 tends to flow well while the longer cute epoxies are encouraged to flow with a hair dryer.
 

Jeff

Jeff
Corporate Member
Is there something better/cheaper?
West System 2 part epoxy is better than Bondo (a type of plastic and fiberglass) for woodworking crack and knot filling/stabilizing. CA glue (cyanoacrylate) works well for narrow small cracks but it doesn't fill gaps and voids.

 

Roy G

Roy
Senior User
John, you could cut a dutchman to cover the knot holes. The defects could be filled with epoxy. I try to use sanding dust to make a paste with the epoxy and force it into the cracks.

Roy G
 

JimD

Jim
Senior User
I bought some water based putty, I think it is ZAR, when I was refinishing a floor. I got red oak color which was a good match. It has stayed in the floor and I've been using it on other situations with good results. You can get it at big box stores but they may not have nearly all the colors they offer.
 

Sourwood

New User
Graham
For big voids, I like to use Rangate Knot Filler. It’s just so much quicker than epoxy. Quite a few color options to choose from - I stocked up on black. The product looks like a beefy hot glue stick (I use a cheap full sized hot glue gun instead of the gun they sell). Shoot it into the void, drop a block of aluminum on top to squeeze it into the nooks and crannies, then after 30 seconds or so, use a plane iron to shave it flush (it’s relatively soft).

If you have a very large void on a table top, epoxy may be a better bet because it’s much harder. Rangate Knot Filler is soft enough to slice with a plane iron, but it’s plenty hard for almost all furniture use in my experience.

Unlike epoxy, you probably shouldn’t use it before machining you’re lumber, as it’s probably going to melt and gunk your cutterheads.
 

Rwe2156

DrBob
Senior User
I use West System III epoxy and tint with either acrylic paint or transtint dye.

A heat gun will pop the bubbles.

Large knots will often need two applications.
 

Wiley's Woodworks

Wiley
Corporate Member
Our fellow woodworkers have mentioned several different materials to use, with epoxy being the most popular. I'll throw my mixture into the ring. When matching the color of the wood, I get my best color matches mixing sanding dust, preferably 220 grit but down to 120 will work, with clear Gorilla Glue. Don't use the standard Gorilla Glue that expands when exposed to water. The clear glue penetrates, dries hard, but can still be worked with a plane or sanding. It wouldn't take any extra effort to mix in color (like the coffee grounds) to get a color contrast if that's what you're after. My 5 different commercial fillers are just drying up because using sanding dust from the exact wood I'm filling gets the best color match.
 

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