How to fill pinhole size pores in crosscut circle slab

[Steve Schwab]

I have a very large (60 inches) diameter live edge crosscut slab of Suar (Acacia) wood from Indonesia. I'm building a table with it. The slab was originally finished with Minwax Polycrylic water based urethane. It needs to be refinished and I want to use an oil based polyurethane to bring out the spectacular grain on the piece. I'm experimenting on the bottom side right now. I have sanded the old finish completely off. The wood has very small pinhole size pores. The polyurethane will not fill the holes and leaves small pinholes all over the surface. I have tried using a wash coat of shellac and then tried filling the pores with a water based filler. Even with the filler thinned down, it wouldn't get into the holes. I tried forcing it in with squeegee and burlap. No good. So at this point I think I need to simply spray shellac, sand, spray more shellac, sand, etc. until I have a smooth surface.
Anyone have another suggestion.

[Todd Burch]

Shellac would be good choice.

You said you sanded the old finish completely off, and I hope that meant the whole slab and not just the bottom.

I used to occasionally have problems with pinholes in wood before as well, and I learned, through observation, that it was caused by me. It was caused by me allowing the wood to change temperatures too quickly during the finishing process. The wood was in my cool garage, and since it was a nice sunny day, I took the piece outdoors to finish (no overspray in the shop, better light, less fumes for me - all kinds of rational reasons). But, when the sun hit the wood, the air/moisture/whatever in the wood decided to expand, and poof, poof, poof - this warming/rising air would burst tiny pinholes in my finish at the same time it was trying to cure.

Could this be your issue?

Todd

[Steve Schwab]

Todd thanks for the reply. I intend to finish both top and bottom. Right now experimenting with the bottom so I don't screw up the important part. I'm pretty sure this is not a temperature problem, as I have not moved the piece and it's in a conditioned environment. As I look closely at the surface, the pores are clearly in the wood itself. I would expect it's the cells or pores of the wood that I'm battling. The hole diameters are less than a 32nd and they all close together.
On another forum, I had someone suggest a thinned down plaster of paris mix squeegeed into the pores. He said it will dry clear. Then a sanding block with 320 grit. Will give it a try and report back.

[Scott T Smith]

I have successfully filled small holes in the past by applying an oil based finish (such as BLO or tung oil), and wet sanding it with a random orbital sander. The resulting slurry will fill the holes. Usually I have to repeat it 3 - 4 times to get them totally full, but once filled they tend to blend in with the color of the wood.