Thread: How to fill fine cracks in hardwood table top ?

The sanding sealer is not a crack filler, and often is not even a grain filler. It's designed to stiffen the surface wood fibers so that subsequent finish coats don't raise the grain.

You could try a flood coat of thin epoxy squeegeed into the surface that you subsequently sand off. Sorry but I can't recommend a brand of epoxy, but epoxy viscosity is typically a function of the hardener used and the temperature of the mix. Epoxy manufacturers' web sites usually have the information needed to pick the appropriate hardener (fast, slow, normal) for the viscosity (runnyness) you would need for a flood coat.

Alternatively, you might be able to fill the tiny cracks if you use a burnished oil finish. If I understand the process, the oil / sanding dust slurry produced when burnishing might fill the cracks for you. IIRC, LGS is the expert on burnished oil finishes

use Timbermate as a grain filler. Heat it in a microwave to make it into a slurry which you can wipe over, grinding it in as you go. Go a bit darker then the natural timber.

Originally Posted by ian

You could try a flood coat of thin epoxy squeegeed into the surface that you subsequently sand off.

Yes the epoxy I use is reasonably low in viscosity. The flooding technique did not work on the fine cracks. Although the sanding sealer is less viscous than the epoxy that still not get absorbed into the cracks when I flooded the cracks. I reckon something like super glue would run into the crack but then superglue has no gap filling capabilities. Or does it?

Hi Harry Wall,
Being a Woodturner, I come across a few cracks.
I'm a great believer in Loctite 401, & Sawdust.
You wood have to have a bit of a scrape to get the stuff out that you have tried to fill it with, then use an old Tooth Brush to clean it properly. Other S/Glues I know nothing about, as all I use is Loctite 401.
406 is very runny, but 401 is really great to work with. If you have no Dust, then make some, right coloured wood & just sand the wood in the Lathe, & let it fall onto a bit of paper.
Try not to get it to full as you will the have to sand it back. So a bit of 401, cover it with dust, & Tamper it down, & if the glue shows through, just add Dust, & give it 4mins. should be ready to lightly sand with say 320/400 paper.
By the sounds of it you will have to cut the whole Table right back.
The Loctite & Dust will go a little dark, but it will be good job.

Originally Posted by harry wall

Yes the epoxy I use is reasonably low in viscosity. The flooding technique did not work on the fine cracks. Although the sanding sealer is less viscous than the epoxy that still not get absorbed into the cracks when I flooded the cracks. I reckon something like super glue would run into the crack but then superglue has no gap filling capabilities. Or does it?

I'm thinking of a flood coat that is as runny, or runnier, than paint thinner.

What finish to you want to use?
Many of the film forming finishes can be thinned for the first few coats which should aid penetration into the fine cracks.

But what is your concern regarding the fine cracks?
Can you post a photo?

I plan to finish with the Wattyl Xtra Clear water based estapol.
My concern with the fine cracks is that since it is a dining table:
(a) running my hand over the surface gives a rough feeling over the cracks and I prefer the surface to be consistently smooth (or consistently rough),
(b) more importantly, over time moisture ingress into the cracks will cause dirt to build up and potential uneven movement of the timber in that area.
I'll post a photo today.

Personally I wouldn't stress too much. Fill them as best you can before finishing, with epoxy, CA glue, timbemate etc etc. Apply a sealer coat and if that reveals more unwanted cracks, fill them again. From there I would sealer again (depending on what I did to fill the cracks the 2nd time) or hit it with a few coats of the estapol and call it a day at that. It may sound like a rough as guts approach, but it isn't.

Here's a photo of some of the fine cracks - after sanding the sealer coat.
20161103_093006.jpg

Originally Posted by harry wall

Here's a photo of some of the fine cracks - after sanding the sealer coat.

OK, what I think you have are surface checks which are a drying defect rather than structural cracks per see.

Are the boards recycled? They look like they maybe.

Opinions will vary, but I don't think that either super glue or epoxy are the best way to deal with these cracks. Do you have any way of measuring the moisture content of the boards? I'm thinking that if the boards are below EMC, maybe you should be wetting the wood with demineralised water to increase it's moisture content. That action might close up some of the smaller checks. But trying to increase the moisture content pre-suposes that the table you've build will not blow apart if the top expands.

I'm then thinking that you will need to resurface the top and start again. If you can take the top somewhere it can be fed through a wide belt sander, you could apply a burnished oil finish where teh combination of oil and sanding dust will fill the checks.

If that seems too much work, I think you should be looking at a thick film finish, probably 2 pack estapol.

Originally Posted by ian

OK, what I think you have are surface checks which are a drying defect rather than structural cracks per see.

Agreed.

If you can take the top somewhere it can be fed through a wide belt sander, you could apply a burnished oil finish where teh combination of oil and sanding dust will fill the checks.

This is my preferred approach too. Well... maybe not burnished, but wet-sanding the first coat or two of oil anyway. The slurry makes a great filler.

An advantage of using an oil rather than an epoxy/estapol is if the timber is still reaching EMC then there's a good chance you'll need to touch up the finish within the next year or so anyway and this is an area where oils excel; you often only need to give the surface a light sand to clean up/key before applying a new coat.

Originally Posted by Skew ChiDAMN!!

Agreed.



This is my preferred approach too. Well... maybe not burnished, but wet-sanding the first coat or two of oil anyway. The slurry makes a great filler.

An advantage of using an oil rather than an epoxy/estapol is if the timber is still reaching EMC then there's a good chance you'll need to touch up the finish within the next year or so anyway and this is an area where oils excel; you often only need to give the surface a light sand to clean up/key before applying a new coat.

Guys, explain this to me. if you fill the gaps with sanding sludge, then put a coat of oil over it, then what stops the filler from coming out when someone wipes it down with a rag, or maybe upends a wine glass on it. It's just dust and oil after all ?

Genuinely curious to understand this .

We're talking Danish, Tung and similar burnishing oils here, not the stuff that stays liquid in perpetuity like raw Linseed or Machine Oil.

With the first one or two coats the oil will penetrate into the timber and the oil/dust slurry will set quite nicely in the cracks, as though it were a combination of end-grain sealer and Timbermate.

After the first or second coat, subsequent coats will start to apply a thin film over the surface that sets with time, similar to applying shellac. The more coats you apply, the glossier the end result.

You must give each coat enough time to set properly before applying the next coat though. Typically a day or two, although some, such as 100% Tung Oil, I've found are best applied a week apart. Usually, it's just a case of following the directions on the side of the can to the letter. No shortcuts.

Originally Posted by Arron

Guys, explain this to me. if you fill the gaps with sanding sludge, then put a coat of oil over it, then what stops the filler from coming out when someone wipes it down with a rag, or maybe upends a wine glass on it. It's just dust and oil after all ?

Genuinely curious to understand this .

this is how I understand the chemistry

you sand the first coat of oil while it is still wet to form an oil and sanding dust slurry -- in the case of the boards we're discussing you might need to add additional wood flour to get enough slurry. As this oil dries it polymerizes setting the "sludge" in the cracks.
Further coats of polymerized oil form a film protecting the set "sludge" from future damage. Years ago I saw a table which had about 10 coats of Feast Watson's tung oil floor finish on it. The table looked gorgeous.

The OP's table is salvageable, but will IMO require a bit of work.


Looking at the picture again, if the boards are salvaged timber, the drying checks could be relatively old.

If you indeed used recycled timbers, I think that it's all part of the look and feel of the table. Assuming the cracks are just surface cracks and not actually continuations through the timber I think enough coats of danish oil or similar would highly reduce the feel of them.

I have had luck in the past with using epoxy and to get it into smaller cracks and voids I bought a load of syringes off of ebay with fine tips (careful you don't prick yourself) and this way you can inject the epoxy where you want it with a good deal of accuracy.