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The piece I am currently working on does not need to be perfect in any way, I am actually going for a slightly rough look (due to many mistakes along the way) but I would like to hide some of the larger imperfections. I got lazy with some of my cuts and I now have a few odd gaps. I remember hearing a while ago that sawdust and wood glue can be used as a wood filler to fill in gaps and imperfections. I would buy proper wood filler but I would rather not spend the money and I am also curious if this technique is realistic.

Is this a method that can work and if so, how?

Also how might this effect finish the piece, if I was to stain the wood would the filler stand out and be very obvious?

  • The answers below are great. And like graphus said when mixing with wood glue it will turn dark. Which I very much back up. But then I tried just putting some glue in the crack/hole and rubbing sand dust over, which on a smaller scale works very well. That could be another option for you to try. – Ljk2000 Apr 21 '17 at 12:55
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Yes, that is a method still in use. You can use it to fill gaps. But, the unfortunate thing about this method is... You create a place on wood that is different in absorbing the oil/stain that you apply. But it depends on your stain colour and wood's colour also. If they are both darkish, it will not be a problem. But if your wood is lightish and the stain is darkish... voila, you will get a whitish spot on wood, in places filled with the wood/glue. Because of its altered absorbance of the stain due to glue. Sorry for my poor english, but I hope that helps.

  • Perfect, that is exactly the confirmation I was looking for. Do you have any idea how best to mix the sawdust and glue in terms of amounts or should I just sort of eyeball it? – Gareth Shepherd Apr 19 '17 at 17:47
  • I just mix in an amount when they become hard (but also as soft) enough to play with. You can adjust the exact combination by adding more wood or glue. It should be like a play dough; it should stay where you apply, but it should also be able to soft enough to fill in gaps. – borgs Apr 19 '17 at 18:18
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I remember hearing a while ago that sawdust and wood glue can be used as a wood filler to fill in gaps and imperfections.

Yes you can do this, but note that the term "sawdust" might be slightly misleading here. Commonly when this sort of thing is done at home it uses sanding dust, not actual dust from sawing which would tend to have a range of particle sizes including some much coarser flakes and generally you want the filler dust to be as fine as possible.

I would buy proper wood filler but I would rather not spend the money and I am also curious if this technique is realistic.

Actually in a lot of ways I think you're better off not buying wood filler. Most commercial wood fillers are slightly disappointing in some way and if you have a ready supply of wood dust already it is a good way to make use of at least some of it.

Also how might this effect finish the piece, if I was to stain the wood would the filler stand out and be very obvious?

If you stain the piece yes it will tend to stand out, usually very obviously.

Most fills made from wood dust and adhesive (including epoxy, white and yellow glues and superglue) are not absorbent and will therefore stand out very noticeably if you then stain, since that relies on absorbency. So an alternative approach used historically was to stain first and then use a filler that matched the stained colour (or often one shade darker), although unfortunately this approach isn't generally practical with glue + wood dust fills because of the need to scrape or sand the filler flush.

If you're not staining
You will at some point read online that if you make a filler from the dust of the same species as the wood you're working on that "It's a good colour match." and even sometimes that "It's a dead-on match." but I can tell you that in most cases those are lies or the person writing is being too generous!

In almost all cases the fill will be significantly darker than the surrounding wood. The reason for this is that the dust has been wetted by the glue so it's behaving quite like end grain, which when wet shows up darker than face grain.

Stainable fillers
This is one of the reasons to not buy commercial wood fillers by the way, because even the "stainable" ones tend not to take stain that well.

There are a few formulas posted online for DIY fillers that stain far better than any of the commercial versions according to their users. Most include some plaster or spackle in the mix to increase absorbency.

But on a smaller scale if you use sanding dust from the same species and hide glue as the binding agent you can get a very reasonable colour match that isn't obvious from arm's length and occasionally even closer. Such a filler can even have good staining properties, but the type of stain you use will matter so no guarantees here and you'll need to experiment for yourself.

Further related info:
Large hole filler products, what is available

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I use a cabinet scraper on a piece of scrap to create the dust, mix with glue until it has a putty like consistency, and the press it into the gap with a plastic spatula (I use the end of my glue brush). I've had very good luck with this not being super noticeable on cherry boards finished with natural Danish Oil. But how it will effect you project specifically depends on what kind of wood and finish you are using.

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The very best way to fill small cracks in raw wood that's going to be varnished is is mix fine sanding dust of that specific wood with a little varnish of the kind you plan to use. The exact proportions aren't important, but the resulting paste should resemble Plastic Wood wood filler. Use a putty knife or similar instrument to force the paste into the crack. Let it dry, then sand smooth. Then when you varnish the piece, there won't be any difference in appearance between the filled crack, the adjacent areas that got paste on them, and the rest of the piece.

  • This is a good filler but there is some variation from species to species with how well it actually matches the colour of face grain. And I would bet that the makeup of the varnish will play a part too, since some varnishes are much higher in oil than others. – Graphus May 8 '18 at 11:46
  • As long as you use sanding dust from the same wood as you want to fill, and use the same varnish that you will use on the piece, the match should be excellent. The advantage is that no matter how much the filler gets on the adjacent wood, after sanding and varnishing the piece the adjacent wood will show no difference in color at all. This is unlike other kinds of fillers that do affect, and therefore change the color of, the adjacent wood after varnishing. – Fredric Blum May 9 '18 at 13:00
  • Just like with filler made from dust and hide glue this does work great on a good many woods, uniformly coloured woods that is, but how about zebrano? Rosewood? I know those are extreme examples but even just pine and other softwoods are cases where this doesn't work as well because of the colour difference between the earlywood and latewood. These get mixed together in the dust to make a middle-ground colour that matches neither. – Graphus May 10 '18 at 12:23
  • I think you're missing the point. The point is the medium, not the dust. The problem with any kind of medium except varnish is that the medium necessarily fills the pores of the wood adjacent (near to) the crack you want to fill. Therefore, when you later varnish the piece, the nearby areas won't take the varnish the same way as the raw wood will. The solution is to use varnish as the medium, which effectively pre-varnishes these areas so when the piece is later varnished, there won't be any difference in color or anything else between these areas and the rest of the piece. – Fredric Blum May 11 '18 at 12:56
  • Your point about the final appearance of the adjacent areas is perfectly valid and it's not lost on me, but you're missing my point about of the colour match of the fill itself. No point in going back and forth on this any more, we both agree that this is a good filler material which is the main thing. – Graphus May 11 '18 at 13:28
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Filling surface cracks on a hardwood tabletop or other flat surface:

After final dimensioning (usually by tracksaw) I use that slightly coarser dust and with gloved hand push a heavy pile of the dust back and forth across the joints. The dry heavier particles fill any voids and still look smooth and perfect.

Next I use a very diluted water to glue (75-25%) and a brush to pour on and brush back and forth again across joints letting the paint brush collect the glue mixture and loose sawdust. As you go back and forth across the joints this mixture will be squeegeed into any remaining voids.

When finished use brush and lightly knock off the remaining dust and let dry for an hour under a fan. Sand with 320 grit paper and immediately apply a first varnish coating.

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