This question really needs more info to give you a good answer: What kind of cracks/gaps are you trying to fill, and why are they present? What is the outcome you're desiring with the filler? Are you asking about grain filler--or "mistake" filler? How big are the gaps you're filling? Are they pinholes, nail holes, gaps between joined pieces, splits in the wood, covering screw heads, etc? Each requires a different approach.

If the crack is so big that the filler is cracking you might consider putting in some wood shims/slices and gluing them in place--or use sawdust and hide glue as a paste.

I usually use Timber Mate for some small gaps or holes (non-structural) or for some contrasting grain-filling--or AquaCoat for creating a smooth surface in open-grained wood. It's water-based and dries quite quickly.

For gaps/mistakes that need some resilience I used hard-wax melt sticks to color blend with the surrounding wood--but only after the piece is finished.

 

Thank you for the reply!

What I'm trying to fill are mistakes. Joints that are not 100% and where I remove loose knots mostly. So the joint issues are not that big, but the knots can be a bit bigger.

Nails I don't use (at least yet). I try to design around not using them. Only for the back in a rebate where I don't cover the nails I use them.

If I'm placing screws I try to use them where they would not be visible.

When I glue I find that the glue to be ugly with my finish. It ends up being more shiny than the rest of the project.

The gap that cracked was from an early project. It was a bookshelf from laminate wood boards. The wood boards had a chamfered edge an I filled the chamfer where the boards met perpendicularly.

 

Famowood filler.
Famowood

 

My favorite filler is a mix of hide glue and saw dust from the project. Hide glue plays better with most finishes compared to aliphatic resin glue.

 

This is what I was gonna say. I have a bottle of hide glue and it's really only ever used to make filler.

I did use it for a couple of other things.. like the leather face on my leg vise. I used it because you're supposed to be able to heat the glue up and remove it, but I haven't had to test that theory just yet..

It depends though. Hide glue is good for big cracks.

I use shellac a lot too though for the fine stuff, like dovetail imperfections.

Spread shellac with an artist brush very liberally where you need to fill, cover with sawdust, dip brush again and just touch it up the line, maybe 1/32 each time, you're trying to make the shellac soak all the way down and outwards. Cover with more saw dust. Rub at it with your thumb a bit and do any touchups but make sure it's higher than the wood. Let it dry for an hour and sand.

The good thing about shellac is it dries very fast. You don't have to walk away for hours to finish. I hate getting that far and having to stop for the night just to let some minor thing like that dry. With shellac you can almost just keep on going.

 

You could try mixing saw dust with wood glue, or pack saw dust into the hole and fill it with thin super “CA” glue.

 

Hide glue does work well with nearly all finishes, and should solve the finish problem you have had in the past (test it though!). PVA glues/sawdust have caused me troubles like you suggest, and using hide glue basically eliminated the glue-splotch issue. Hide glue is water-soluble, and maybe the shininess can be wiped away with a wet rag on the surface.

I like the CA glue gap-filling comment--I've done that too, and it works well with finishes. I'd fill knot holes with epoxy--or maybe even colored hot-melt glue stick (I haven't tried this, but have seen others do this). Or drill them out and patch, like another comment suggested.

 

Thank you for all the comments. Seem like that a common consensus is that I should try hide glue. I'll see if I can source it.

Also, seems like I should fill knots with wood and fill only the gaps that remain.

I've got some epoxy but I'm not sure if it is suitable for deeper pours. It's 5mm I think (less than 1/4") and it's clear. I was going to use it to seal the surface of OSB for a cupboard.

 

A lot depends on what you're druthers are for presentation... I usually use Timbermate, however, if I want a more realistic filler, I resort to my bottled sawdust.
While the colour might will not be a perfect match, it gives a contrast that is more finish friendly than the original sawdust stiffened with CA/PVA glue.

Having said that, for knots would suggest (as others have), CA'ing it in place and backfill with a contrasting Timbermate (or such)... usually ebony. Just remember that most glues will alter the finish penetration/hue... as well as UV over time... so highlighting may be a more optimum option.

 

I like this for filling knots

 

Timbermate is my usual go to, however I also have Plastic wood for deep fills below the subsurface then Timbermate to finish. I havent tried Starbond but it looks OK too, its not a local buy in, so mail order is required for it. I am not sure what they would have used on Pastor Pio's hands, ... but might check