SealCoat and Oil Finishing Questions

by the Message Board

Tim asked, "I like to use oils because of how it brings out the wonderful grain patterns and the depth it gives, plus it's wipe on. I just bought 2 new products I've never used before.

1) Zinsser "seal coat"

2) Rock hard table top varnish

Now I know I'll use the rock hard as my last couple of top coats, but when would I use the seal coat? Before the oil, after oil, or both (doesn't sound correct but I've heard of it), or shall I try just a couple of coats w/ the seal coat then right to the rock hard?"

Hope this makes sense.

Thank you very much,

Tim

Sam Simpson: "Although it is possible to get away with all kinds of finish combinations, it is always best to use a single product system. So, if you can think of no special reason to use the seal coat, leave it out.

The varnish you have selected is a full bodied product. The best way to lay down a base for it is to thin the first coat with turpentine. Often called a sacrificial coat because you will sand most of it off. You might even consider thinning your second coat slightly and applying it as a wiping coat. When applying the final full bodied coats, you might try a little trick I use. Have a hair dryer standing by, if you get a few bubbles that are not flowing out as the finish stiffens, hit them with a blast of warm air from the hair dryer. This usually results in a smooth flawless finish.

Dust is the demon. Keep it at bay by spritzing around the area with water in a trigger spray bottle before you start each step.

Some useful links:

Michael Dresdner: Zinsser SealCoat is compatible and appropriate under ALL common finishes. It is sold specifically as a universal sealer for this reason, so it is the one product you can feel confident putting under anything.

That said, I will also tell you that oil based varnishes, such as the Rock Hard you mentioned, almost never need sealer of any kind under them, as they are self sealing.

The fastest, most efficient way to seal raw wood with an oil is to scrub it onto the wood just as it comes from the can, using Scotchbrite as an applicator, and wiping off the surface immediately with paper shop towels. Do not thin the material, as that only serves to apply less material per coat, and make air bubbles more likely. (It is a common myth that adding thinner will make the resin penetrate deeper, but that is not the case in this situation, as the common thinners for oil based varnishes are only diluents, not solvents for the resin. It would be akin to adding water to a handful of marbles with the expectation that they would then "penetrate" through a sieve.)

If you want to read a concise technique guideline on this method, follow the link.

Hawkestone Pete: Where on the web, might I find pages describing the properties of finishing oils? Using an oil is my preferred finish. What I think is happening, since I am relatively new to ww'ing, is that I don't have a strong enough understanding of the product, and therefore am not getting the results I seek.

I have brand favourites at this point, being Watco natural Danish, and circa1850 antique, depending on tone and shade changes I want. Understanding the properties though, I suspect will get me to where I want to go. I don't like getting results "by accident" especially on an expensive board.

Sam Simpson: Pete, I like your understanding and approach to the problem. Unfortunately I don't think you will find the answers you are looking for scattered on the web. Not because the information is not up there, but because I haven't found it all in one place. So how will you be able to piece the puzzle together if you don't first have a good picture.

I think your best bet is to find a good used book shop. You need to be looking for books on finishing circa 1920 - 1950. It was in that period that the sciences were still connected to trade learning and understanding. Since then, other than some of the names mentioned below, I have only seen publications that hint about the science while sketchily giving overview to craft and trade.

A little note here, I'm English and don't have too much breadth on the American scene. But the books you need will answer the questions; What is polymerization, What is Saponification, What is the difference between long chain and complex molecular linking, What is the difference in thermosetting and thicksosetting. They should have lists of long oils and charts of viscosity.

If you do find it necessary to use the Internet, start with searches in the materials conservation field. You will find the science of finishes there. WAG archive home is one place to look JAIC online and another Canadian Conservation Insitute (CCI) and another JP Getty - AATA Online As I say, these folks know the science, but the craft is in the hands of their technicians.

There are several good books written by technicians, Bob Flexner comes to mind. He has a way of explaining things that click with most folks.

And finally I will stick my neck out even further and say that being self taught can only get you so far. To have a full understanding of any subject you need the benefit of one or more good teachers.

To my mind, the greatest thing that Ellis has done in setting this site up, is to give access to many good technicians and scientists, such as Michael Dressner, Jeff Jewitt, Mac Simmons and Russ Fairfield and others. Not only do we get the opportunity to cross check our facts and share information with each other, but also to answer questions that we find interesting. I would say that you have already found the best source on the Internet, for finding facts on Woodwork and finishing.

One of my teachers, (probably my Father) instilled a strong notion that after having learned something well, and having practiced it to a high level of skill, the next thing to do is pass it on. The circle is not complete until the knowledge is successfully passed on. I don't have the patience, nor could I afford the pay cut to become a collage lecturer, like my Father, so I am thankful for this site and the ability to pass on what I know.