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Thoughts on Finishes

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Blog entry by Clint Searl posted 01-16-2012 03:39 AM 2753 reads 10 times favorited 19 comments Add to Favorites Watch

Thoughts on Finishing and Finishes

What follows is my experience derived expert opinion.

All finishes are based on either drying oils or resins (or some combination of the two). Drying oils such as Boiled Linseed Oil and Tung Oil, which are commonly used in wood finishes, dry (cure) through a polymerization reaction in the presence of oxygen. BLO and Tung Oil are usually heat treated to speed up the chemical reaction, but can also be used raw. Resins, which are the bases for film finishes can be either polymerizing or hardening by solvent release.

A few words about so-called Sealers. There’s no such thing because there’s nothing to “seal.” Any finish, be it oil or resin based, needs nothing under it to perform its intended use. The argument that a “sealer” allows the top coat to adhere is specious. If the final finish won’t stick to the wood, then it’s the wrong finish to begin with. The argument that a “sealer”, shellac in particular, is needed to prevent a stain from bleeding into or reacting with a top coat only means that the stain and top coat should be compatible, thereby voiding any need for an intermediate barrier. And as far as a “sealer” filling the open grain before the top coat film finish, the top coat will fill the grain just as effectively without the added complication of a different formula. Simply consider the first (thinned) coat of the final finish to be the “SEALER.”

On to the individual finishes:

• Linseed Oil – Raw linseed oil is useless to the woodworker, and used outside it’ll turn black from mold. Boiled linseed oil is next to useless to the woodworker. BLO is slow to cure and offers no protection from anything, regardless of the number of applications. The prevailing myth is that it makes the grain “pop.” Rather, its dirty amber cast highlights contrasts in the grain by making some areas muddier than others while making any wood dull and lifeless. The best use for BLO is as an accelerant for fire bugs.

• Tung Oil – Raw tung oil is the consistency and color of warm pale honey that can be applied directly to bare wood, highlighting the grain and imparting a clear warm glow. Application is wipe-on/wipe-off, which can be made easier by mixing it with an evaporative solvent like mineral spirits or naptha. Multiple applications will produce a close-to-the-wood finish with pretty good resistance to many household liquids. The drawback to using raw tung oil is the long time it needs to cure, days and days rather than hours. Tung oil that has been heat processed and combined with solvent vehicles and driers does cure within hours so that multiple coats can be wiped or brushed on in a shorter time. Once the initial coat is well into polymerization, subsequent coats will cure faster. The most popular brand is Waterlox, which expensive at around $30 a quart and once opened it will want to jell whatever’s left in the can. However, Waterlox does deliver on its claims and returns a handsome finish. Caveat emptor: Many products include Tung Oil in their names while they have none or only homeopathic amounts in their formulas; there’s no Truth In Labeling Law when it comes to paints.

• Shellac – It’s been around for a long time as a finish, either brushed/sprayed on or as a high gloss French polish. Forget about French polish; it’s not worth the steep learning curve and fussy process when better alternatives are out there. Brushing it on ain’t no cakewalk either. It tends to streak and brushwork needs to be fast and sure to prevent earlier coats from softening and being pulled. Also, it has poor resistance to water and household chemicals. Finally, if you want your furniture to be your legacy, shellac will eventually dry out, crack, and flake away. Sealer? Bah!

• Oil Varnish – The predominant contemporary varnish is Polyurethane, a manmade resin based, tough and durable film finish that’s highly resistant to water and household chemicals. Its amber tone imparts a strong warming cast to the wood. It’s easy to apply by brush or wiping and cures enough over several hours to reapply, which can be a drawback, as a fully polymerized coat will inhibit adhesion of a later coat. Recoating intervals should be kept to 24 hours or less to avoid that potential problem. Poly is available in a range of sheens and, once fully cured, can be rubbed out with wet sanding, steel wooling, and polishing compounds. It’s a finish that one can learn to love for its friendly application requirements, physical properties, and appearance. Those who demean it haven’t learned to use it.

• Waterborne Polys and Acrylics – My experience is limited to the brands usually stocked at retail stores, my favorite being the Varathane line. Available in several sheens, it goes on easily with brush and can be built up with successive coats in a couple days. I haven’t tried it, but I’ve seen work that’s been sprayed that is indistinguishable from other fine finishes. Soap and water cleanup. It cures to a durable resistant finish, and in the version made for floors that contains aluminum oxide, it’s as tough as any other finish – great for tables that are gonna be danced on. It can be rubbed out just like oil polys. Some folks see a bluish cast in it, but rose colored glasses will fix that.

• One-Part Nitrocellulose, Acrylic, and Alkyd Solvent Lacquers – The best of all, IMO. With a decent compressor and gun and a little practice, spraying lacquer is the most consistently successful means to a great finish. From bare or stained wood to final coat, application can completed in one several hour session, including cleanup. It’ll go on over dye stains or cured oil stains, and can be naturally toned as in the case of NC or tinted with dyes and other colorants like metallics and pearls to deliver spectacular results. The acrylic and alkyd formulations are water white, allowing the wood’s natural beauty to be revealed. Available in various sheens straight from the can, they can also be rubbed out and polished. They’re tough enough for kitchen and bath use, and a ding in the finish years after the original can be erased with a fresh application that melts into the old. Sherwin-Williams is my preferred brand.

• All Other Finishes – No experience; no opinion

That’’s my story and I’m sticking to it,
Clint

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been



19 comments so far

View bluekingfisher's profile

bluekingfisher

1038 posts in 1635 days


#1 posted 02-01-2012 11:00 AM

Thanks for the info on finishes Clint. There is so much to choose from (and be confused by) The Advertisement agencies have done us no favours in describing the products, often inaccurately. This said for the weekend WW there are some good proeduts from the can which help bring a decent finish to a project.

As creature of habit I tend to find a product and stick to it. It;s just when I change the wood species I usually thiswork with can throw up problems which are not apparent with the previous timber, so some more research is required. This can be fun at times but a pain in the arse at other times, particularly when youi don’t necessarily have the time on a particular project.

Anyway, thanks for the insight.

David

-- No one plans to fail, they just, just fail to plan

View HamS's profile

HamS

1168 posts in 1044 days


#2 posted 02-01-2012 12:35 PM

What is your view of the lacquers in a spray can. I have not made the investment in a decent spray gun and have a bit of trepidation about the time needed to clean up the bits of a spray gun, especially for a small project, which most of my work tends to be. I find myself actually finishing many of the pieces before the the final assembley because it is much easier to touch up a joint line on the inside of a carcase if the glue squoze out onto the plastic film of a good finish rather than raw wood.

-- My mother named me Hamilton, I have been trying to earn my nickname ever since.

View Clint Searl's profile

Clint Searl

1455 posts in 1017 days


#3 posted 02-01-2012 05:13 PM

HamS…...I think the rattlecan lacquers are as durable as canned acrylics, though I only use them on cigar box sized projects. It’s easy to spray too much at a time, making runs and sags a potential problem.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View a1Jim's profile

a1Jim

112093 posts in 2232 days


#4 posted 03-11-2012 09:37 PM

Hey Clint
I just found this post ,I agree with most of your thoughts especially on BLO and Linseed oil being of any real use as a finish. I’ve found that a lot of folks like what’s easy and not necessarily a good finish and the stick with it because that’s the only experience finishing they have using their outdated and non protective product. It’s been years since I’ve used Nitrocellulose lacquer but I do recall it was easy to shoot and touch up, I was always under the impression that Nitrocellulose lacquer was much more subject to degradation due to ultraviolet light then Acrylic lacquer.
This was a very good summery of many of the finishes available and I hope the folks that think BLO is the only way to go take note and try some of the finishes that are truly protective and versatile products that you suggest.

-- http://artisticwoodstudio.com Custom furniture

View Clint Searl's profile

Clint Searl

1455 posts in 1017 days


#5 posted 03-12-2012 02:49 AM

Jim….I’m in the process of using NC on a project currently underway that I’ll be able to post in about a week.
My experience using NC over the past several decades hasn’t included any obvious degradation due to UV exposure, but I can’t say that they have been subjected to very much. The one I’m using now is Sherwin-Williams T70FT1.

For some guys, BLO is a religion. LOL

Clint

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View Trapshter's profile

Trapshter

62 posts in 1049 days


#6 posted 03-12-2012 03:27 AM

Great Post! Love it! . I offen tell people BLO is not a good finish. Nice to see I m not the only one.
Jm

-- Smile and wave boys just smile and wave

View NormG's profile

NormG

4175 posts in 1659 days


#7 posted 03-12-2012 04:05 AM

Well I guess I was doing something correct all along and did not know it. I have never used BLO, just Tung Oil and Poly’s

-- Norman

View a1Jim's profile

a1Jim

112093 posts in 2232 days


#8 posted 03-12-2012 04:09 AM

I’ve used Sherwin Williams Pre-cat it’s great material but I don’t do enough finishing to avoid the waste involved with it’s shorter shelf life.
I’ve also used some water base Lacquers and like that their fumes are less aggressive and still deliver a nice finish.

-- http://artisticwoodstudio.com Custom furniture

View Clint Searl's profile

Clint Searl

1455 posts in 1017 days


#9 posted 03-12-2012 12:29 PM

I stick with NC and CAB because they’re foolproof: appearance, durability, repairability,easy to use, cleanup, and infinite shelf life. I’ll give up NC and CAB when they pry the cans out of my dead lifeless hands.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View Clint Searl's profile

Clint Searl

1455 posts in 1017 days


#10 posted 03-12-2012 08:26 PM

Jonathan, I appreciate the comments re pre-cat, but the factors that keep me wedded to NC and CAB are shelf life and recoat. It may take me a year to use a gallon, so a short shelf life would mean a lot of waste, and I know that if I come back to a piece to hit it with more finish, both NC and CAB will burn in and integrate with the original. Also, if I haven’t used a gun in a while and some residue is hardened around the needle, it’s easily washed out with acetone.

I’ve thought about using waterborne and even have a couple cans, but just can’t come up with a reason to give them a try. Before the Feds take solvent lacquers off the market, I’ll stock up on enough to last me for the rest of my woodworking days.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View Earlextech's profile

Earlextech

979 posts in 1346 days


#11 posted 03-12-2012 09:36 PM

Clint, I appreiciate your regular guy approach to finishing materials. I always tell woodworkers that finishing is not as difficult as some will have you think. In my almost 30 year career I have basically used 5 finishes, paint, lacquer, poly, shellac, tung oil. These few finishes have carried the weight of thousands of kitchens over the years. I would encourage eveyone who is timid about finishing to take this list as a calling to finish your projects using any of these simple finishes Clint mentions.

-- Sam Hamory - The project is never finished until its "finished"!

View Clint Searl's profile

Clint Searl

1455 posts in 1017 days


#12 posted 03-13-2012 12:22 PM

Jonathan, thanks for setting me straight about burn-in. Shelf life remains a show stopper to my using precat.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View Kenny 's profile

Kenny

260 posts in 1103 days


#13 posted 03-19-2012 08:00 PM

I disagree with your statement about sealers, shellac in particular, as them not being needed if the finishes are “compatible”.

A water-base top coat will dissolve a waterbase dye or stain and can cause the color to run or migrate in the topcoat. And if you happen to get a run, something that happens to the best of use, and you didn’t seal the color before applying your top-coat, your run will pull color with it. A simple 1lb cut of shellac between the color and top coats will remedy this beautifully.

As well, what are your thoughts about Blotch Control? Most consider it a “sealer”. Is that not needed as well? How else do you avoid blotching when staining or dying blotch-prone woods like maple, cherry or pine?

Sorry, I think a lot of this is too “one dimensional” and doesn’t deal with the issues that arise when layering finishes, as is common in fine furniture.

-- Kenny

View Clint Searl's profile

Clint Searl

1455 posts in 1017 days


#14 posted 03-19-2012 09:09 PM

Kenny,
A water-base top coat will dissolve a waterbase dye or stain and can cause the color to run or migrate in the topcoat. And if you happen to get a run, something that happens to the best of use, and you didn’t seal the color before applying your top-coat, your run will pull color with it.That’s a non-issue by choosing a stain that won’t disolve into the top coat

As well, what are your thoughts about Blotch Control? Most consider it a “sealer”. Is that not needed as well? How else do you avoid blotching when staining or dying blotch-prone woods like maple, cherry or pine?I don’t worry about blotching because I don’t stain cherry or maple that I use.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View Purrmaster's profile

Purrmaster

799 posts in 748 days


#15 posted 11-17-2012 01:38 PM

Thank you.

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