Dull spots in tung oil finish

[Ben Hatcher]

Here's a quarter sawn fumed white oak table top I'm working on. Hopefully you can see the dull spots in the photo. I've put down about 7 coats of oil, the first being a slurry sanding to fill the pores. My question is this, are those dull spots in need of more coats, a good buffing, or an indication of something else?image.jpg

[Randy Goodhew]

Here's a quarter sawn fumed white oak table top I'm working on. Hopefully you can see the dull spots in the photo. I've put down about 7 coats of oil, the first being a slurry sanding to fill the pores. My question is this, are those dull spots in need of more coats, a good buffing, or an indication of something else?image.jpg

Did you use real tung oil or something that contains tung oil?

Blessings.

[glenn bradley]

If it is a true oil it will penetrate but, not form much of a film. The 1/32" thick sprayed polyurethane finishes that some commercial shops use will hide many sins, oils don't so much. I mostly use penetrating finishes, oils and oil blends, and consistent surface prep is paramount as irregularities only get amplified, not hidden. I'm no expert and I'll do my best judging by the pic. In order of guess, it looks like that area:

1 - is just an area that had different absorption qualities and should be re-flooded (preferably during the same period as the rest of the surface).
2 - wasn't surface prep'd the same as the rest of the board due to height irregularities (lower portions missed some of the surface prep method as it passed by).
3 - has a contaminant that effected the oil (this is my last choice due to the irregularity of the shape).

Fortunately we have a few finishing wizards on here and I hope they will chime in.

[Scott Holmes]

What finish did you use? "Tung oil" could be one of several different finishes, each with it's own traits, pro's and cons.

Most don't even have tung oil in them. Pure tung oil would not be a good choice of finish for a table top.

[Ben Hatcher]

The label on the oil I used reads "Woodcraft Tung Oil 100% Pure". The first coat was thinned 50% with turpentine as the label instructed. It is possible that the patches are due to different surface prep, but I spent a considerable amount of time prepping this piece sanding 80-150 with festool paper, changing every 15 minutes, 220 and 320 with abranet, then used the norton abrasive pads, green, maroon, grey, and white. Here's some additional information that might help, it does seem that the dull areas are more frequently located in spaces with more open pores, when I push my fingers across the table, they chatter ever so slightly but the suface feels glassy smooth, and when I rub the area that are dull with a cloth, they look just as shiny as the surrounding areas...temporarily.

[Scott Holmes]

You do realize that this talbe will need almost constant upkeep. It will be easy to do; but it will need to be done often.

Also be aware that water from a sweating glass will get into the wood! Tung oil and other pure oil finishes ARE NOT good at sealing the wood to protect from liquids.

Option: add a bit of varnish to your oil and turpentine to make an oil/varnish blend and you will better protect your table.

FYI: Turpentine evaporates slower than mineral spirits; neither make the tung oil molecules smaller or go deeper into the wood.

[Prashun Patel]

I would try adding a little bit of varnish to the oil to see if you can get better sealing of that area. Still wipe on and wipe off.