Archive for the 'Finishes' Category

Wood Finishing with Allan Lacer

Saturday, May 6th, 2006

In today’s MWA meeting world-renowned turner Alan Lacer talked about wood finishes, specifically how they apply to wood turnings. It was a whole-day meeting at Jim Sannerud’s shop in Ham Lake. It has to be said that Jim went above and beyond to make this an enjoyable day, many thanks to him!

I was utterly amazed by the entries for the egg challenge. All the entries did deserve a price, they were just awesome. Great work!

But let’s get to todays topic: wood finishes for turners. Below a (brief) summary of todays session.

Preparing the wood

Finishing the wood starts with the last cuts on the lathe. When turning for example a bowl within one revolution on the lathe the wood will be cut with the grain in some sections, and across the grain in others. That can easily lead to tear out, which is not easy to sand away. Also excessive sanding can bring a piece out of round, as the sand paper cuts different across and with the grain.

Sharp tools and a gentle cut can leave a surface that doesn’t require much sanding. A bowl gouge with an Irish grind (many variations are known as fingernail grind, Ellsworth grind etc.) can be used for a light shearing cut or shear scraping by using the sides of the tool presented at a steeper than usual angle.

Another option is to use the burr of a scraper with the scraper on edge so that just the burr cuts at an angle to the wood. For a finishing cut the burr of a grinder is usually to aggressive. For finishing Allan takes the burr of with a honing tool, then creates a new lighter burr with a burnisher.

Fine paper-thin shavings are a good indication of a light cut suited for finishing. These cuts are not very hard, learning them will make finishing much easier.

Sanding

Choosing the right sand paper will make this job much easier. Alan’s favorite is a purple ceramic-based sanding paper from 3M, currently only available commercially or in large quantities. Another choice is the 3X paper from Norton. I have been using that paper exclusively for the last 2 years, it is much superior to other papers I have tried. It doesn’t load easy and seems to cut for a long time.

When sanding on the lathe avoiding sanding rings is important. For bowls using and angle-drill with a cup (soft or hard) and a sanding disk makes sanding on the lathe (with the lathe running relatively slow) fairly easy. And the two opposing motions help avoid sanding rings. Finishing up to (depending on wood) 220 to 380 grid leaves a surface suited for finishing.

I do not have a angle drill and use the papers ‘by hand’ with the lathe running. That works, albeit slower. To avoid visible sanding rings using this method one has to go to a higher grid, depending on the wood I typically go to 400 or 600 grid.

When sanding spindle work, end a sanding grid by stopping the lathe and sanding larger flat sections with the grain. That avoids the most visible sanding rings.

Safety: Sanding generates fine dust that is quite hazardous to your health. Prolonged exposure can even trigger allergies. Collect the dust at the source! I use a section of flexible metal dryer duct connected to my dust collection piping. The duct can be aimed at wherever the dust is produced. This is an efficient and low-cost method.

Finishes

Choosing a finish is not easy, there are many factors to consider. If in doubt, try a sample piece, especially with finishes that are not easily removed. Some of the deciding factors are:

  • Desired appearance: Glossy or flat, finishes that leave a film or are ‘in’ the wood, color
  • Ease of application: Wipe on (on the lathe or off), spray finishes etc., required equipment
  • Speed: Drying time, curing time, time between re-application
  • Repairability, reversibility, renewability, durability
  • Health concerns

That last point requires special attention. Pretty much all finishes available today are save for contact with food when fully cured (which can take some months for certain finishes). Salad bowl finishes or finishes for use on toys are nothing but re-badged common finishes. A cured finish leaves behind substances that are actually used in food production (mineral oil, plant-based oils, shellac, wax), or substances that are inert (film finishes such as polyurethane or varnish).

However during application the solvents used in most finishes are toxic. Nitrile gloves and in some cases respirators are strongly recommended. Environmental concerns (solvent release into the atmosphere, proper disposal of left overs) may further sway you to avoid certain finishes.

Safety: Note that rags used to apply most finishes are a fire hazard due to the heat generated during the drying process! Keep used rags outside, or in a water-filled bucket. Do not simply throw them in the trash!

Drip test

Many finishes these days do not list ingredients, making it very hard to predict their performance. Even worse, some finishes have a limited shelf life (sometimes as little as six months) but do not list a date.

A very easy way to evaluate a finish is a drip test: Apply a few drops of finish on a piece of transparent plastic. From this you can tell drying time, color, hardness when dried and or cured (not the same). This often allows to determine likely ingredients of a finish, and more importantly gives you data for some of the basic parameters of a finish.

Oil finishes

Mineral oil (which is suited for human consumption) is frequently used for food bowls and cutting boards. It is transparent and does not change the color of the wood other than the wetting effect common to all oils, which often highlights the beauty of the grain. Mineral oil penetrates the wood and helps it resist moisture. However it does not cure and requires regular re-application. Mineral oil is available at grocery stores.

Nearly all other oils used in finishing cure eventually. However the do not build up significantly, so they do not tend to create a finish with a deep luster. Drying time varies but is generally very slow.

Tung oil is a favorite among the oils. It comes from the chinese tung nut, and has a very unique scent. Application is simple: flood the surface, let it penetrate for a while, then wipe off the excess. It does cure, and is used in many coats can create a very slight build up. It has a yellowing effect, which makes it less popular for light colored woods. Shelf life is almost unlimited. Care must be taken when purchasing tung oil. Many products using the name tung oil or even pure tung oil contain additional ingredients or sometimes no tung oil at all.

Walnut oil is another favorite. Cheapest source is the grocery store. It is a bit lighter in weight then tung oil and does not build up.

Linseed Oil (or BLO, Boiled Linseed Oil) is another commonly used oil product. It has a lot of tradition, because it was one of the most commonly available oils. But in my humble opinion it is not a very good finish. Protection value is minimal, durability low. Though it may be suited for mixing with other finishes (see below).

There are some specialty oils available for finishing, such as polymerized tung oil (a favorite for gun stocks) or polymerized linseed oil. These oils cure much faster than their non-polymerized base materials, and may even build up a finish. However they are quite expensive.

Film building finishes

Varnish

Varnish is another very traditional finish. It is durable, alcohol and water safe. Traditionally it comes in soft, medium and hard varieties, and sometimes with additional properties such as UV protection etc. It is a film finish that stays on the wood and builds up with repeated application. One of the problems of Varnish is that today it has become a synonym for a very large family of finishes with vastly different properties. Many manufacturers do not list ingredients, and it is impossible to tell if they started with a good quality varnish or not.

According to Allan one of the better brands with consistent high quality varnish is Waterlox.

Oil-Varnish mix

Oil-Varnish mixes have been popularized by Sam Maloof. They attempt to combine the ability of oils to pleasantly highlighting the grain with the protective qualities of varnish while trying to avoid it’s sometimes plasticky ‘on the wood’ appearance. It is available in many varieties, containing unknown quantities of ingredients and solvents.

Allan recommends mixing your own. The traditional Sam Maloof formula is pretty well known:

  • 1 part Boild Linseed Oil (for it’s drying ability)
  • 1 part pure 100% tung oil (for it’s beautification ability)
  • 1 part high quality solvent/oil(!) based varnish or polyurethane

Spar varnish is not suited as it is to soft. An example for a suitable varnish is Behlen’s rock hard table top varnish.

The above mix results in a pleasing and durable finish, suitable for items handled frequently. At least three coats are recommended, wait at least two days (better two weeks) between coats.

Lacquer

Lacquer is a finish that creates a clear, very high-gloss film finish. It dries extremely fast, in fact consumer-grade Lacquer typically contains retardants to make it dry a little slower so it is easier to work with.

It is liked by many turners as it is easily available, fast to use with predictive results. The downsides to Lacquer are the strong fumes it creates during application and while curing. Some people also do not like it’s appearance, which can be cold.

Water-base finishes

This group of finishes mostly consists of water-based (or water-borne) polyurethane. These finishes dry fast with little odor. But the film finish tends to leave the wood cold, and it tends to build up with a bit of a haze. However these finishes are a relatively recent addition to the finishing market, and given fast-paced development they hold promise for the future.

Shellac

Shellac is a great finish that many think will have a renaissance. Shellac comes in flakes produced by the female shellac bug for protection. It is available in various colors from very light blond to a fairly dark color, all also available de-waxed. Once the flakes are dissolved in denatured alcohol, shellac is ready to use.

Shellac has a lot of great properties: It can go above or below any other finish (the only finish that can do that), is easily applied and repaired, new coats slightly dissolve and bond with previous coats. It creates a great looking finish which can be buffed to a mirror sheen.

Shellac also is a finish that minimizes vapor penetration into wood, preventing wood from moving.

Downsides are that it only tolerates moderate handling, which makes it unsuited for items such as pens. However most commercial pen finishes contain mostly shellac and wax, because they are easy and fast to apply with a great appearance. But they are not durable enough for day to day use.

Also once shellac is dissolved in alcohol, the shelf live is approximately six months. The alcohol changes the chemical makeup of shellac, and after a certain period it will no longer cure properly.

In some cases the color of shellac can also be a problem, though the blond varieties are very lightly colored and typically just add a bit of warmth to the wood.

For starters Allan recommends to get some light and some dark de-waxed flakes. Colors in between can be achieved by mixing these varieties. Mixes suitable for turners are 1.5 to 2 pound cuts, meaning 1.5 to 2 pounds of shellac per gallon of alcohol. Obviously that is a rather large quantity, so divide into smaller equivalent quantities. 4 ounces to a pint also results in a 2 pund cut.

A great french polish type finish that is very fast to apply and dry can be achieved by mixing shellac with oil (tung oil, BLO etc), shellac in an amount equalling about 3/4 of a jar of baby food with about a table spoon full of oil. Application is much like a friction type finish: use a lint-free cloth with very little texture and apply the mix on the wood spinning in the lathe. It builds a very nice sheen in a hurry and dries to the touch within seconds.

Wax

Wax is the closest to no finish at all. It is easy and fast to use, but does not stand up to use making it suitable only for decorative pieces or to give a piece that extra sheen to facilitate sales by applying on top of other finishes.

The best of the waxes is carnauba wax. It is fairly hard and at least somewhat durable. However it leaves a slightly cold looking finish. Beeswax leaves a warm finish, but is very softy. For this reason folks sometimes mix waxes, for example by adding a bit of bees wax to carnauba wax. The waxes can be mixed by heating in a double boiler, or the can be made into a paste by adding turpentine.

Common floor waxes can also be used. However one should make sure they do not contain the solvent toluol, as that can react with other finishes to make them milky in appearance. There are also health risks involved with toluol.

No finish

Some oil rich woods can be polished to a great luster without the use of any finish at all. Cocobolo is one such wood, and in fact finishes do not easily bond with cocobolo because of it’s high oil content. Another wood that can come out great without finish is bloodwood.

Finishing the Finish

The appearance of some finishes can be further improved by polishing the finish, though care must be taken to not work through the finish. Finishes should be thoroughly cured (and therefore hardened) before polished. Traditionally compounds such as Pumice Stone & Rotten Stone were used for polishing. These days however many polishing compounds found in automotive departments offer a easier and faster to use solution, though it requires a little experimentation as the abrasive quantities of such compounds are not known until tried.

Another buffing solution are the Beall buffing wheels.

Sometimes it is also desirable to flatten the appearance of a finish. For this Allen recommends a steel-wool like synthetic product from Germany which is making an appearance in the US market.

Rockler Polyurethane Satin Gel Finish

Monday, October 3rd, 2005

In a couple of forums turners were remarking on the great results of Rockler’s new Polyurethane Satin Gel Finish. Now I had tried an oil & Urethane blend before on some turnings and was not impressed. I had hoped that the oil component would make the finish get into the wood a bit. But I found that it was hard to apply evenly, it had the on the wood feel of PU typical finishes, and if anything the oil made it cure much slower. So my expectations were not high, but respecting the opinions of my fellow turners I decided to try it anyway.

I am glad I did! In a first attempt I used it to finish a simple Pine Bowl of the lathe. The bowl was sanded to 400 grid on the lathe. I then took it off and applied the first coat of the gel finish. It was very easy to apply an even thin coat. After drying overnight I gave it a light sanding with 600 grid and applied a second coat, repeating the process with a third coat. I was rewarded with a very thin but even and hard satin finish. And it does not have the on the wood look at all.

Some turners also remarked that it can be buffed. I will have to try that soon.

Beall 3-On Lathe Buffing System

Wednesday, August 10th, 2005

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While on special at Woodcraft I picked up the Beall 3-On Lathe Buffing System. I liked the idea of having all buffing wheels right there next to each other without having to change tools. I had never buffed my turnings before, so I was pretty amazed what a shine this simple device can create. For my taste using the third wheel with the Carnauba Wax creates even a bit too much of a sheen, though my wife likes it.

In general the system works well, though one really has to hold on to the wood. The wheels really like to grab it and fling it across the room. For larger pieces the wheels are a bit close together and get in the way. And obviously the wheels will not get into the inside of bowls or boxes, I guess for that I’ll have to look for alternatives like the bowl buffs. Lastly sometimes it is a bit hard to get the mandrel out of the lathe, the taper really likes to jam in there.

Had I to do it again I probably would look for the individual wheels.