the holly grail of exterior wood finish

[mjscottinnc]

In the search for the holly grail of natural looking exterior wood finish.

First, many will tell you that selecting ‘exterior’ wood and applying no finish at all is the way to go, it is the easiest way to go for sure. I’ve tried it with and without a finish; I enjoy the look, smell, and feel of wood as it comes off the plainer so I don’t mind a little work to keep that way.

I tried 9 recipes:

#1 – 1/3 turpentine - 1/3 Boiled Linseed Oil (BLO) – 1/3 Oil Varnish
#2 - 1/3 turpentine - 1/3 Boiled Linseed Oil (BLO) – 1/3 Oil Varnish – Japan Drier (JD)
#3 – 2/3 Spar Urethane – 1/3 BLO
#4 – 2/3 Spar Urethane – 1/3 BLO - JD
#5 – 1/3 Spar Urethane – 1/3 Mineral Spirits – 1/3 BLO
#6 – 2/3 Oil Varnish – 1/3 BLO – JD
#7 – Minwax Wood finish Puritan Pine
#8 – Minwax Polyshade Honey Pine
#9 – Weston Teak Finish

The JD was added at a rate of two caps per gal.

The test wood was 4/4 Mahogany planed one side with a clean end grain cut. I evaluated each test piece for depth of penetration in the end grain, ease of applications, shine, odor, and post drying finishing. All test pieces had four applications of finish, allowed to dry for 30 minutes at which time all excess was wiped off and then allowed to dry for 24 hours.

Results:
#1 – penetrated 1 inch, easy to apply, lots of smell, very dull, smooth surface feels oily
#2 – penetrated 3/4 inch, easy to apply, virtually no smell, very dull, smooth surface feels oily
#3 – penetrated 1/2 inch, easy to apply, no smell, satin luster, very smooth surface
#4 – penetrated 1/2 inch, easy to apply, no smell, satin luster, very smooth surface
#5 – penetrated 1/8 inch, easy to apply, little smell, dull, smooth surface
#6 – penetrated 1/16 inch, easy to apply, little smell, dried so fast that wipe off made finish very dull, surface swirls
#7 – penetrated 1/4 inch, easy to apply, little smell, dull, smooth surface
#8 – no visible penetration, easy to apply, little smell, High Gloss, rough surface

FYIs: All the finishes had the same look, very little color difference, even the ones with stain. Adding JD seems to quickly release the agents of odor. #6, #8, and #9 would require post drying work to remove particles on the surface.

I was looking for a finish that has a satin luster (a tiny bit of shine).

My conclusions: for an oil finish I’d pick #2, for a little bit of sheen #4. Best overall #4

 

[CarvedTones]

Where were your results for #9? If that is Watco (I didn't find Weston) then it is more Linseed. I would have included some tung mixes in the test also. Something like this:
http://www.realmilkpaint.com/finish_decks_porches.html
http://www.howardproducts.com.au/products/tung_oil.htm
though I often use terps instead of orange oil and you can substitute tung for BLO in some of your recipes and you should see improvement. I have been using the stuff for several years on outdoor projects with great success.

 

[Howard Acheson]

I'm a little confused. What was it you were trying to evaluate? All I can see is assessments of appearance. Appearance is only a small aspect of exterior finishes. There is no evaluation of protective qualities, durability and long term aspects.

For example, urethanes are a poor finish for exterior applications even if they claim to contain UV inhibitors. UV rapidly attacks urethane causing it to become cloudy, more amber leading to cracking and peeling.

Another point about your testing process. The way to measure and evaluate finish penetration is to apply, let dry and then crosscut the finished area. Then observe and measure the penetration. Using this process I would expect about a few thousandth's of penetration in mahogany.

 

[mjscottinnc]

Sorry forgot about #9, I actually did it first.

#9 - no visible penetration, easy to apply, no smell, Glossly, rough surface

I used to use tung all the time while I was in PA, but could not find any locally so I used BLO for the testing. Good tip though.

 

[mjscottinnc]

All valid points, yes the test pieces were allowed to dry before they were crosscut to observe penetration. I figured that if I could not see penetration with normal magnification, I wasn't going to grab the microscope to get the absolute extent of penetration. Anyone can evaluate the results in relative terms. Owning a wood sailboat for over 30 years I'm very familar with both Spar Varnish and Spar Urethane and I prefer the later, just personal preference. Thanks for your comments.

I'm a little confused. What was it you were trying to evaluate? All I can see is assessments of appearance. Appearance is only a small aspect of exterior finishes. There is no evaluation of protective qualities, durability and long term aspects.

For example, urethanes are a poor finish for exterior applications even if they claim to contain UV inhibitors. UV rapidly attacks urethane causing it to become cloudy, more amber leading to cracking and peeling.

Another point about your testing process. The way to measure and evaluate finish penetration is to apply, let dry and then crosscut the finished area. Then observe and measure the penetration. Using this process I would expect about a few thousandth's of penetration in mahogany.

 

[CarvedTones]

Sorry forgot about #9, I actually did it first.

#9 - no visible penetration, easy to apply, no smell, Glossly, rough surface

I used to use tung all the time while I was in PA, but could not find any locally so I used BLO for the testing. Good tip though.

You can find the pure tung at the woodworking stores or order it from Milk Paint or other places. The "Tung oil finish" products are all over the place, but they are really similar to your #2 mix, only with spirits or other similar solvents instead of terps.

Howard doesn't like tung; we have debated that from time to time. He is highly regarded as a finish expert, so I don't understand why my personal experience and his opinion are so far apart, but they are. I have had bench slats last a very long time exposed year around (they are several years old now), boat handrails last a long time and done a few other tung and terps applications that live outside with good results.

 

[mjscottinnc]

Yes it was Watco (spelling corrector made the change), that is the reason for the test. I purchased Watco Teak finish. I expected to find teak oil in the can (I use it on the interior of my sailboat and did not want to drive to the marina to get some) to my surprise it was not teak oil it was as you state (oil / varnish mixture), so I decided to use it and see what happened. The reason for the testing was to find a mixture that would give me the results I was looking for. Only time will tell how well it holds up outside. That is dependant on a number of uncontrollable variables which include total UV exposure, moisture, salt or fresh water, mechanical ware, etc, etc all of which is beyond the extent of my testing.

I, like you, have gotten excellent results with finishes that other deem ‘not the best’. I’ve been happy and ultimately that is all that counts.

You can find the pure tung at the woodworking stores or order it from Milk Paint or other places. The "Tung oil finish" products are all over the place, but they are really similar to your #2 mix, only with spirits or other similar solvents instead of terps.

Howard doesn't like tung; we have debated that from time to time. He is highly regarded as a finish expert, so I don't understand why my personal experience and his opinion are so far apart, but they are. I have had bench slats last a very long time exposed year around (they are several years old now), boat handrails last a long time and done a few other tung and terps applications that live outside with good results.

 

[richlife]

I'm a little confused. What was it you were trying to evaluate? All I can see is assessments of appearance. Appearance is only a small aspect of exterior finishes. There is no evaluation of protective qualities, durability and long term aspects.

For example, urethanes are a poor finish for exterior applications even if they claim to contain UV inhibitors. UV rapidly attacks urethane causing it to become cloudy, more amber leading to cracking and peeling.

Another point about your testing process. The way to measure and evaluate finish penetration is to apply, let dry and then crosscut the finished area. Then observe and measure the penetration. Using this process I would expect about a few thousandth's of penetration in mahogany.

Basically, I agree with Howard. I'm not taking a shot at you, Mike, but after a number of tries to come up with a long-term, exterior finish, I read you post hoping to find something that will last. As Howard, pointed out, you didn't address that.

I've tried most of the variations you tried and more, but find that none of these provides long-term protection. Using a wood like mahogany is fine, but the wood itself is the primary protection you have against deterioration and decay. The finish will need to be renewed at least annually. With other woods (say pine or hickory as examples), these finishes really won't keep them from decaying if they aren't well maintained (little natural anti-rot properties).

My reasons for wanting exterior protection is that I've done a number of carvings intended for exterior use (one example is a sundial). Without pretty constant attention, they will soon look bad and, depending on the wood, could even decay. Since they are carvings, it's not a simple refinish like a handrail on a boat. One piece that I originally did as a test piece is in pine and has been a true bear to keep in decent shape. (Most of my efforts are now in black walnut, cherry or mahogany, so at least that has long been addressed.)

Some time back, Andy suggested that the simplest and probably best approach would be to use a straight oil finish (he may have said tung oil -- I'm not sure). That's actually what I'm working on next and hoping for better results. Even if I have to refinish every few months, it will be easier and better than the effort of refinishing a varnish in a carved configuration. (I'll use BLO, not tung oil. My experience with tung oil is that it doesn't do well in direct sunlight.)

I'd certainly be interested in anything else that you or others have to say on this.

Rich

 

[CarvedTones]

Tung and terps is my favorite for things that get wear living outside, like bench slats. I reapplied based on observed condition rather than a schedule. Bench slats were lasting over one season between treatments; they did begin to gray but still shed water. Boat rail was getting treated a couple of times a season to be kept bright. Treatment is being wiped with a rag of the mix after brushing with hard plastic bristles to clear dirt. You can get UV protection added to Tung from Milk Paint (vendor site), as without it as Rich mentioned it will not hold up as well plus it darkens. But I think it is more durable that BLO. I do also use BLO. I am using it now on a rustic shaving horse.
One of the things i like about oil is that if you wait a little too long to reapply, you get a little weathering but can reapply right over it. If varnishes begin to peal and crack, repair includes removal.

 

[mjscottinnc]

Well, now I'm the one who is confused. The first boat I built had a companionway door that I made out of mahogany. I finished it with four coats of thinned Spar. It was docked at the marina year round and it was exposed to the elements 24 / 7 / 365. I refinished it ever two to three years. I owned that boat for 18 years before I made a next one.

Notice: To all who read my first post, it is intended to be informational only. It is not a declaration that my findings were in anyway a life test or that anyone should act on my findings. Given the current state of the art, I’m happy with the results I have been getting and continue to get. These are my personal finding that I thought I would share. I will have to think twice about doing that again. Bye.

Basically, I agree with Howard. I'm not taking a shot at you, Mike, but after a number of tries to come up with a long-term, exterior finish, I read you post hoping to find something that will last. As Howard, pointed out, you didn't address that.

I've tried most of the variations you tried and more, but find that none of these provides long-term protection. Using a wood like mahogany is fine, but the wood itself is the primary protection you have against deterioration and decay. The finish will need to be renewed at least annually. With other woods (say pine or hickory as examples), these finishes really won't keep them from decaying if they aren't well maintained (little natural anti-rot properties).

My reasons for wanting exterior protection is that I've done a number of carvings intended for exterior use (one example is a sundial). Without pretty constant attention, they will soon look bad and, depending on the wood, could even decay. Since they are carvings, it's not a simple refinish like a handrail on a boat. One piece that I originally did as a test piece is in pine and has been a true bear to keep in decent shape. (Most of my efforts are now in black walnut, cherry or mahogany, so at least that has long been addressed.)

Some time back, Andy suggested that the simplest and probably best approach would be to use a straight oil finish (he may have said tung oil -- I'm not sure). That's actually what I'm working on next and hoping for better results. Even if I have to refinish every few months, it will be easier and better than the effort of refinishing a varnish in a carved configuration. (I'll use BLO, not tung oil. My experience with tung oil is that it doesn't do well in direct sunlight.)

I'd certainly be interested in anything else that you or others have to say on this.

Rich

 

[Tom Rioux]

The problem with BLO is that it is food for mold. This is especially important in our area. It's just raw linseed oil with driers. It gets some filtering but compared to a well produced linseed it is dirty. Long term durability suffers because it doesn't have the body that develops from a quality refinement process.

Same thing with Tung Oil. It's a little better than BLO but in harsh, WNC exterior conditions it falls apart in about 3 months, just like BLO.

Both oils are really only something I trust inside.

For exterior use, that holds up, you need the right kind of oils. Tung Oil and Linseed Oil are both refined for this purpose. I've never seen these made available to consumers.

Typical isocyanate produced urethanes fail quickly outside but there are some Aliphatic Urethanes and Cashew based technologies that provide outstanding results. You need really, really tough resin if you want to hold that "fresh of the planer" look.

Mahogany wood types vary greatly. Most of what I've seen lately is African Mahogany. This is an exotic hardwood full of tannic acid. It needs to be sanded aggressively with 50 grit and then washed with Lime Clean to neutralize the tannins before it really takes in a serious resin. You can oil it as described above and it looks pretty nice but to really saturate those dense fibers the only thing I've found that works is open up the pores and neutralize the tannic acid. If you dump pure turpentine on Mahogany that is not prepped it usually on penetrates .5 to 1 mil at best. So if you want resin to get into that wood it needs some help.

I started a QUV competitive comparison this spring in Asheville. It spun out of control and now I have hundreds of exterior wood panels with various finishes and wood types. I decided to do a separate study on Western North Carolina exterior finishes. So while we do the QUV runs in the lab I'm also comparing exterior wood finishes and wood types in moderate sun southern facing and high mold northern facing conditions.

I'd be glad to have any recommendations of finishes and wood types to include if any one here wants to see how something compares. It could be as simple as finish a piece of wood and send it to me.

I'm taking pics at 6 month intervals.

 

[richlife]

Tom, would you consider opening a new thread (using an appropriate title) with this post? I think it would be of great interest to many. I also have some questions about your study and think a new thread would be a better place for that.

First question -- when did this start (so that says when your first six month interval is).

Thanks, Rich

 

[Tom Rioux]

It's a June and January check point. So it starts in June. But boards can go in at any check point.

 

[eyekode]

Mike, I for one thank you for the post. It started a good conversation.
Salem