I got this question from a friend and thought I should share my answer on the blog because it addresses several issues. Here’s the question:
I was reading about finishing hickory and most people seemed to like pure tung oil cut with mineral spirits. How does this sound to you? 50/50 or a bit more tung oil? Also, this is for a table similar to a sofa table that my daughter will place near her front door. So should I topcoat it with polyurethane thinned 50/50 with mineral spirits?
It seems to me there are four issues here. How to finish hickory; using tung oil; thinning half with thinner; and more specifically choosing a finish for a table near a front door.
First, hickory. You choose a finish for any wood for three reasons: whether or not you’re using a spray gun (choose a fast drying finish if you are and a slow drying one if you’re not, which I assume is the case for you); for the protection and durability that the finish provides; and for appearance. I don’t see that hickory would warrant any special considerations, such as being prone to blotching. For protection, especially near a front door, you need a little thickness to protect against water. For appearance, the main difference besides being able to build a little thickness for protection is between all finishes and water-based finish. All finishes except acrylic water-based finishes add some yellow/orange coloring. Acrylic water-based finishes don’t. I think you’ll be happy with a little color, and water-based finishes are more difficult to use.
Second, tung oil. One hundred percent tung oil (as opposed to thinned varnish, which is often deceptively labeled “tung oil”) is difficult to use. You need to apply five or more coats, sanding between coats to remove the roughness and allow several days for each coat to dry before sanding. You also don’t get any build to speak of. Tung oil exists as a finish because in the 1960s and 70s Homer Formby sold thinned varnish labeled tung oil. He created the reputation and the market with zillions of live appearances and TV infomercials, but he was deceiving people because he wasn’t selling tung oil. He was selling varnish, which I think is a much better finish. So, though you can use 100% tung oil if you want to, I recommend against doing so.
Third, thinning. I don’t see any reason to thin any finish except to make it 1) easier to apply, especially through a spray gun or by wiping, or 2) get the finish to flow out more level (reduced orange peel or brushmarks), or 3) make it possible to apply a thinner build. There’s no issue with bonding, which is the reason usually given. As long as the wood is clean and not sanded to too fine a grit (say to 320 or finer), all finishes bond well.
Fourth, near a front door. You need protection against water (coats, umbrellas, etc.), which means getting some build. It’s not the finish itself, but the build, that is most effective at blocking water penetration. So you need a finish that dries hard. For your situation, without a spray gun, I suggest either polyurethane, maybe thinned with about 10% mineral spirits to reduce brushmarks, or a wiping varnish, such as Minwax’s Wipe-On-Poly or General Finishes Seal-A Cell or Arm-R-Seal, all of which are varnishes thinned about half with mineral spirits. The one downside to wiping varnishes is that they are all glossy after several coats, so you may want to rub the final coat with #0000 steel wool to make it satin.
I don’t know why you would start off with tung oil, then follow with polyurethane, except to get more color. But boiled linseed oil will give you a little more color than tung oil, and also dry faster.
– Bob Flexner