What works to fill a knot hole? - Woodworking Talk - Woodworkers Forum
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post #1 of 32 Old 07-11-2020, 07:29 PM Thread Starter
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What works to fill a knot hole?

Preferably something I can secure from a big box store, also I would like it to be clear to show the knot.


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post #2 of 32 Old 07-11-2020, 07:55 PM
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what size knot are you talking about ??
any photos ?

.

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post #3 of 32 Old 07-11-2020, 08:27 PM
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If it will be painted, I usually use Bondo Automotive Body Filler. If it will be stained, I frequently do the same, but then use an artist brush and darker stain of similar color to kind of hand paint grain lines, etc across the smooth sanded Bondo. I have tried other things, but never had good luck with them For me, the Bondo works best.

Another way is to drill the knot hole to a known round shape and install a plug that is cut from the a scrap of the same wood. The special plug cutters that are available will allow you to cut a tapered plug with grain lines running across the plug. Use glue and drive the plug into the drilled hole, keeping the grain lines of the plug oriented to match the project grain lines. Drive it in until it is tight and then let the glue dry. Then saw, chisel, sand the excess wood plug until it is flat and smooth with the surface of the project board. You may need to do the decorative art brush technique to this plug too, but it won't need much if you are careful to match the grain lines of the plug to that of the project board.

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post #4 of 32 Old 07-11-2020, 08:53 PM Thread Starter
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Here is an example. There are a couple a bit bigger


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post #5 of 32 Old 07-11-2020, 08:54 PM Thread Starter
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I want to preserve the knot, and have it as part of the piece


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post #6 of 32 Old 07-11-2020, 09:14 PM
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For that knot, I suggest epoxy with a color added that is close to the knot color. Seal the back side and pour the knot slightly over full. When cured sand both sides smooth. It's too close to the end of the board to do much else without destroying the board in the process. Hardened epoxy will machine much like a hardwood. When pouring in the epoxy, heat the surface of the epoxy with a heat gun carefully. It will thin the epoxy and cause the air bubbles to rise to the surface and break, thus making the epoxy more clear. Watch some of the videos about doing this for large natural edge slabs. Matt Cremona has several good videos on Youtube about doing this.

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post #7 of 32 Old 07-11-2020, 09:39 PM Thread Starter
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Thanks, is there a specific brand that you have had success with?

I tried an epoxy as a clear coat on a hundred plus year old bow front dresser that I made into a vanity. The epoxy turned smokey white after 24 hrs and destroyed the top. Im sure it was me in some way that caused that, but JB weld whom made the product offered no definitive troubleshooting.

I ended up making a new top for that, and using poly. Luckily the piece had a trashed top before I ever bought it. Otherwise I would still be trying to remove that coating to preserve the original top.


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post #8 of 32 Old 07-11-2020, 09:40 PM
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Quote:
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Preferably something I can secure from a big box store, also I would like it to be clear to show the knot.


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To make it clear, you can use 2-part epoxy to just fill the little cracks, etc. If the knot wood is going to be gone, you can fill the hole in with 2-part resin, clear or tinted with a little color if you want, or mixed with colorful bits of something glittery, or just sawdust. Lots of creative possibilities. There are YouTube videos to give you an idea..
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post #9 of 32 Old 07-11-2020, 09:41 PM Thread Starter
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Also, the piece in new, and the rest of it has no finish on it, can I poly or laquer over the epoxy?


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post #10 of 32 Old 07-12-2020, 03:27 AM
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Wipe the top down with a damp rag. Often the blush will disappear , if not then sand the top with 320 grit and apply a coat of epoxy again. The top may have been damp when you applied the epoxy, this will cause blush.
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post #11 of 32 Old 07-12-2020, 06:43 AM
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I have a floor of engineered oak 14/3.
Knot holes etc filled with some kind of black resin. Looks OK.
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post #12 of 32 Old 07-12-2020, 07:05 AM
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Normal epoxy is not the kind of clear you are asking for. It is usually somewhat foggy.
You want something that specifically states 'clear' or water white clear. I don't know if you can get that in the box stores. I think your best bet would be to get the regular epoxy, stain it black to fill the holes and sand it level. Then coat with clear varnisg or urethane

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post #13 of 32 Old 07-12-2020, 07:45 AM
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I've filled many knots with West System or MAS epoxy. I put a piece of tape on the underside and fill from the top. Thin epoxy gets into the nooks and crannies best. As Charley said, heating the surface a little with a heat gun or hair dryer helps too. You can thin the epoxy by heating it, but remember that heating it also accelerates the cure time. Use the slowest curing hardener. Regular epoxies like these have an amber color that darkens the wood, but it is a good match for the amber in oil based polyurethane or varnish.
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post #14 of 32 Old 07-12-2020, 08:16 AM Thread Starter
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Im not sure clear is what I want. The knots are dark, so maybe dyed Bondo or a dark wood filler from the back side can work.

I dont need to really even fill the voids. Im mainly after a sort of reinforcement of the places that have knots. Some go strait through.

Can I dye bondo or filler with dark stain then apply it?

I know most fillers dont take stain once cured, will they when wet?

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post #15 of 32 Old 07-12-2020, 08:18 AM Thread Starter
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I like the epoxy idea also. I just hate buying stuff online.

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post #16 of 32 Old 07-12-2020, 09:32 AM
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My go to is West System Epoxy. Probably can't get it in a big box, but you can get it from Amazon, West Marine, or any place that sells boat supplies. There are a variety of additives and fillers you can get, but you will only need the epoxy resin and hardener. They make a standard and slow set hardener. You can also get pumps for the cans that make mixing easy and fast, 1:1 pumping. Depending on the wood I will add a touch of darker color analine dye to the epoxy. But even on clear knots I have had success pouring it in clear since it will transmit the dark colors of the knot surrounding it.
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post #17 of 32 Old 07-12-2020, 10:30 AM
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One more possibility.

On a crack that small, I think you could use fine sawdust and SuperGlue. Locktite makes a version called Ultra Liquid Control that they sell at Hone Depot. You're going to want that control because you want to contain the glue to just the crack. If you get it in other places, it will leave a stain that will show up when you put on your finish. I might even go so far as to tape off the surrounding area.

Create some fine dust, ideally from the knot itself and press it down into the crack dry. Pack it in best you can. I use a dental pick or a toothpick. Level it and brush away the excess. Then carefully drip in some super glue, trying to keep it in just the crack. Overfill it just a tinch so there's a slight "pillow" of glue. Don't overfill it too much because you don't want it running into or onto places you don't want it. The glue will react with the fine dust and cure almost instantly. In some cases, as it cures, it will bubble and blast a little dust from the crack. That's a OK, you just might have to repeat the process. Poke at it with something to make sure it's fully hardened, then sand flush. It's a little harder to sand than epoxy.

As always, test on scrap first.
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post #18 of 32 Old 07-12-2020, 11:04 AM Thread Starter
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I had to get some sand paper anyways, so I while I was getting that, I found some 2 part epoxy made by Gorrila glue thats clear. I got 2 kits for 10 bucks. Im gonna try it on some scrap to be sure it dries clear and is sandable.

If that dont work, I will order the fancy stuff, or see if there is a boat shop near me with hours that fit my needs. As with most specialty type places, they all seem to have bankers hours.

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post #19 of 32 Old 07-12-2020, 12:26 PM
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Quote:
Originally Posted by furnacefighter15 View Post
I had to get some sand paper anyways, so I while I was getting that, I found some 2 part epoxy made by Gorrila glue thats clear. I got 2 kits for 10 bucks. Im gonna try it on some scrap to be sure it dries clear and is sandable.

If that dont work, I will order the fancy stuff, or see if there is a boat shop near me with hours that fit my needs. As with most specialty type places, they all seem to have bankers hours.

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In my experience, those small-batch two-part epoxy kits are intended more as adhesive, and less as filler. I don't think you'll have a ton of success getting it completely clear with no bubbles: Every time I've mixed the stuff up, it's been absolutely full of bubbles. You may have more success than I, however.

For a clear finish, if you REALLY don't want to buy online, a lot of Home Depots carry something called Famowood Glaze Coat, which seems to be your basic tabletop epoxy at a VERY high markup. You could get a small kit of that and apply it in one or two fill sessions, and as long as you follow directions, you should end up with a pretty clear result. However, you'll be getting a lot less bang for your buck than if you ordered something online.

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post #20 of 32 Old 07-12-2020, 01:36 PM Thread Starter
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I just did a little test piece with the gorrila epoxy. It is bubbly for sure, and more of an amber color which both would be fine for this application.

But Ill see if its a go for actual use tomorrow after its fully cured to see if its sandable, and does not turn some wierd color.

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