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The Preface:

I'm building a table for the garden and did some research into how I might seal and protect the most vulnerable parts of the table. The end-grain. The wood I have available is old(30+ years) and very dry larch-wood.

Beside the steps one could take, that are already covered in various questions across this and other sites I stumbled upon a method that is called "sizing". I hope I spelled that right. The sealing of end-grain is covered in 'Do I need to seal the ends of hardwood fence boards?' and this here might be a duplicate to that question.

The Story:

While watching Steve Ramsey's channel I stumbled over his video about 'What You Need to Know About Glue'. He also covers gluing end-grain (starting at ~5:20) and suggests making a "sizing"(at ~6:00), which is basically wood-glue mixed with some water to "size" the wood before the actual glue-up. To me it seems this sizing is just sealing up the end-grain pores with wood-glue. And the mixing with water is done so the thinner substance might penetrate deeper into the wood.

My thought now is that I will try to use this technique for the end-grain parts of my table (probably all of them) to close the pores and make it more durable.

To achieve that I would put masking tape around the edges of the wood and soak the end-grain with my "sizing". The masking tape would protect the surface of the wood from ugly glue-stains during the sizing. After all is dried up I would take off about half a millimeter (~1/64") with the table-saw/miter-saw for a smooth end and start to apply the actual finish everywhere.

The Question(s):

In theory I think this method to be quite ingenious and am wondering why I haven't heard of it before. Or am I missing some fundamental problem with this here?

  • How far will this sizing penetrate into the end-grain? (Of course that answer will probably be dependent on the density and type of the wood)
  • Will this help preventing/delaying rot?
  • Will the masking tape prevent the other faces to get ugly glue stains?
  • Is there any drawback with this method concerning the expansion and shrinkage of the wood? Which will probably be severe as I plan to let the table sit outside all the time.
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He also covers gluing end-grain (starting at ~5:20) and suggests making a "seizing"(at ~6:00), which is basically wood-glue mixed with some water to "seize" the wood before the actual glue-up.

That's "sizing" and "size", see Gluing end-grain.

To me it seems this seizing is just sealing up the end-grain pores with wood-glue.

Yup, as you'll read in the above link that's exactly what it's doing.

And the mixing with water is done so the thinner substance might penetrate deeper into the wood.

Yup.

How far will this seizing penetrate into the end-grain? (Of course that answer will probably be dependent on the density and type of the wood)

Yes it will depend on the type of wood, not its density but how absorbent it is. Red oak for example is much denser than pine but will absorb liquids much more deeply into end grain under normal circumstances because of its structure.

Still, size is normally relatively viscous so absorption should be expected to be fairly shallow, on the order of 2mm at best, which is very approximately 1/16", but possibly as low as the 1/64" that you mention you plan to trim off so I wouldn't do that.

Any anyway I wouldn't suggest you seal the end grain using dilute wood glue.

Soaking finish into the end grain is much more commonly done, but a superior alternative is to coat it with epoxy. See How to Weatherproof Outdoor Furniture by Curing It with an Epoxy Coat on Rockler.

Will this help preventing/delaying rot?

Yes, that's exactly what this is for. By preventing water penetrating deeply into the wood at the end grain (which is far and away the most absorbent surface on any wood) it will greatly slow deterioration.

Will the masking tape prevent the other faces to get ugly glue stains?

Yes. As you'll see on the Rockler link using tape is exactly what they recommend.

Is there any drawback with this method concerning the expansion and shrinkage of the wood?

No.

More details
The Rockler link suggests straight epoxy applied directly to the end grain but that's not always the best idea as epoxies vary in their viscosity. It's best to have an epoxy that's quite thin.

If the epoxy you're using doesn't have the desired flowing consistency its viscosity can be lowered by two main methods: adding solvent or heating. The usual solvents mentioned are an alcohol of some kind, usually denatured alcohol (DA) in North America, or acetone. Note: diluting epoxy does affect its final strength, but for this it shouldn't be a big deal (especially if you don't overdo it, and only a little solvent will be needed to get to the right consistency).

If you want to use heating you can gently heat the separate hardener and resin, or the mixed batch, using a hairdryer or a heat gun. You'll see it immediately makes the epoxy much more fluid. If doing this it's also worth heating the end grain because as it cools it will suck the epoxy deeper into the pores.

  • As usual, spot on, thx @Graphus! I'll fix my spelling so it won't confuse anyone.But i must say that i think "size" as a noun looks rather strange when written. According to dict.leo.org size can be translated to "Leim", which I assumed was just the German word for woodglue. – Stoppal Jun 8 '16 at 16:42

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