I really like to use Minwax Tung Oil Varnish for most of my projects to bring out the best in the wood. I was making a run of small boxes last week and after painstakingly applying 5 or 6 coats of oil to every nook and cranny of these boxes, the maple burl parts took even more, I thought wouldn’t it be easier to just submerge these boxes in finish and let them suck up the oil? Then remove them after a night of swimming and follow up with another coat or two after it has dried. Would this work? It seems plausible, especially for the burl and spalted that seem to soak up their weight in finish. Any thoughts from folks who have tried this?
Jeffrey P. Bengston
Edited 5/2/2002 11:18:58 AM ET by Bengst
Replies
I've done it on unassembled pieces and it is a very common practice for primming wood. I'm not sure how well the excess would drain out of all of the nooks and crannies. You may endup with a runny mess.
Steve - in Northern California
Steve Knight does this with the wooden planes he makes. in the article on his sight he says that after he leaves the pieces in a bucket of sawdust to soak up the excess oil. now that the oil is taken care of you can move on to dealing with the sawdust :) hope this helps
Check out the link below. It explans how Steve Knight does his.
http://www.paragoncode.com/shop/vacuum_pump/
Scott C. Frankland
Newfoundland Wood Worker
A very long time ago, I did my Master's thesis on fluid mass uptake in wood. Most of the books at the time were indicating that fluid viscosity was the primary factor in limiting penetration at any given pressure level. What I found was that it was molecular size (as more or less indicated by molecular weight).
The greatest influence however is pressure. At ambient pressure (such that there is no gradient between the fluid solution and the wood), fluid uptake is minimal at best. The addition of even a small amount of pressure (eg 15 to 20 psi) will greatly increase the amount of retained liquid. You can get this pressure with a bicycle pump! UNDER NO CIRCUMSTANCES WOULD I GO HIGHER THAN 15 - 20 PSI.
I have always wanted to obtain some sort of pressure vessel (I have been thinking of a 5 gallon paint pot) so that I could use it to put a lot of finish into small pieces quickly. I would guess that you could get 4 or 5 times the amount of finish into the wood in a half hour than if you were to soak the pieces overnight. (The curve on penetration tends to flatten out fairly quickly).
Several things have stopped me. The first is the cost of the paint pot -- I never could find one used or one at a decent price. Secondly, you need about 4 gallons of finish. And lastly, if the material is flammable, extreme caution would be required to avoid creating an explosion hazard. For me this latter point was very prominent in my thinking because I wanted to use lacquer.
With an oil based finish, I think you could use some of these nylon putty knives to clean out the corners. You would also get a certain amount of kick-back (after the pressure is released, the wood will retain a certain amount of the pressure and as it equalizes, a certain amount of the fluid would get pushed back out). After scraping out the corners and after equalization, I would simply rub the surface down with rags to absorb excess material and then set them aside to harden/polymerize. Be extremely careful with rag storage and disposal especially with oily finishes.
The pressure would not "hurt" the wood. My guess is that you could get some very significant penetration (depth) and you would actually bulk (fill) the cell lumens with the finish in most of the area of penetration. My guess is that with a one-step pressure system, you could increase your production rate and after finish polymerization, the finish could be rubbed to an incredible luster and smoothness. You would also really go through the finish with 5X the retention
Be aware that if you use any fluid that swells the wood (eg something with water or alcohol) you will induce dimensional change in your pieces that could be disasterous.
>> UNDER NO CIRCUMSTANCES WOULD I GO HIGHER THAN 15 - 20 PSI.
Is that to avoid ignition or avoid bursting the pressure vessel, or both?
>> I have always wanted to obtain some sort of pressure vessel
>> (I have been thinking of a 5 gallon paint pot) ...
Pressure cookers are rated to 15 PSI. I've never seen a 5 gallon pressure cooker, but I have a 2.5 gal. that I got at a thrift store for a very reasonable price. Hadn't thought of using it for finishing, but you've given me ideas.
>> ... if the material is flammable, extreme caution would
>> be required ...
Could you get around that by pressurizing with carbon dioxide? Or some other inert gas, argon, nitrogen, etc? The scenario you describe, with 4 gal. of finish in a 5 gal. pot wouldn't take much gas.
>> You would also really go through the finish with 5X the retention.
Plus this method might be better suited for finishes that cure by solvent evaporation than for those (e.g. linseed oil) that cure by reacting with oxygen. It could take that deeply embedded oil a long, long time to dry. Or maybe you could pressurize it with air in a dry pot to cure.
The net effect of this seems very similar to vacuum impregnation, where you submerge your work piece in finish (epoxy is what I've mostly read about), pull a vacuum on it until the wood stops bubbling, then release the vacuum and let the atmospheric pressure drive the finish into the evacuated wood. The pressure differential is almost the same, and if the pressure vessel fails, it implodes instead of exploding.
Stanley,
It would be really spectacular if you accidently opened the pot before it completely decompressed- especially if you'd heated it.
I wounder if you could pressurize the pot with a hydraulic cylinder (like on a tractor or a wood splitter) without heating it.
Probably it would be a huge cost to set up something dangerous that you could alternatively do with a few extra coats of oil.
Frank
>> UNDER NO CIRCUMSTANCES WOULD I GO HIGHER THAN 15 - 20 PSI.
Is that to avoid ignition or avoid bursting the pressure vessel, or both?
>>>>Commercial wood treating operations will use pressures of 150psi in their impregnation processes. My thesis research and some common sense indicated to me that with pressure finishing, there is no need to fully impregnate the wood. Finishing after all is a surface treatement.
Some pressure treating processes will first pull a vacuum to establish a negative pressure in the wood. After the impregnating fluid is added, the chamber is then pressurized to the 150 psi level.
Pulling a vacuum would be another possible method. I chose a pressure system because I have an air compressor which makes it all very simple and easy. I might consider Frank's use of hydraulic pressure if I had that equipment and understood more completely its mechanics.
There is also the issue of safety; and on this issue, I would alway prefer to be on the cautious side. Other than a bursting pressure vessel, I would be very concerned about releasing pressure and the venting of that gas. If the fluid were flammable, the gas released/vented would be saturated with fluid volatiles and therein could be highly flammable or even explosive.
A long tube from the exhaust port vented to the outside coupled with a gradual release of pressure would be better than simply releasing pressure into the interior atmosphere where you would be working. And if you gradually opened the valve and slowly opened it completely (leaving it open for several minutes before opening the chamber) I am fairly confident that internal vessel pressure would equalize with ambient conditions.
>> I have always wanted to obtain some sort of pressure vessel >> (I have been thinking of a 5 gallon paint pot) ...
Pressure cookers are rated to 15 PSI. I've never seen a 5 gallon pressure cooker, but I have a 2.5 gal. that I got at a thrift store for a very reasonable price. Hadn't thought of using it for finishing, but you've given me ideas.
>>>>I have known some individuals to use pressure cookers to make Slivivitz (excuse my spelling but I was drinking some of this Plum based white lightning when I was also learning how to spell it. Alas the drinking somehow took presidence).
The issue between a pressure cooker and a paint pot is again an issue of safety. You say pressure cookers are rated at 15psi; I think most paint pots normally operate around 50 psi and I think they might have a rating around 100psi. Whatever you do, you do not want to have the bloody thing exploding on you or me especially if the fluid is flammable! I also think that paint pots have been more thoroughly tested in finishing applications while pressure cookers have only been tested for cooking. I do seem to remember that with pressure cookers, they recommend not to fill them more than half way.
>> ... if the material is flammable, extreme caution would >> be required ...
Could you get around that by pressurizing with carbon dioxide? Or some other inert gas, argon, nitrogen, etc? The scenario you describe, with 4 gal. of finish in a 5 gal. pot wouldn't take much gas.
>>>>When I was at OSU (Orygun that is), I wrote an extension publication about pneumatic nailers and staplers. One of the definite no no's was using bottled gas to power these tools. If the regulators failed the tool could explode; I apply the same logic and therein consider any possible advantage of using an inert or non-combustible gas being disproportionately offset by the bottled gas/regulator system.
>> You would also really go through the finish with 5X the retention.
Plus this method might be better suited for finishes that cure by solvent evaporation than for those (e.g. linseed oil) that cure by reacting with oxygen. It could take that deeply embedded oil a long, long time to dry. Or maybe you could pressurize it with air in a dry pot to cure.
>>>>I don't know my chemistry as well as I should in this case but as I understand it, oil finishes harden by polymerization. I do not know if oxygen is required in this scenario. The addition of Japan driers (metallic compounds) tend to act as catalysts. I do know that warmer temperatures promote polymerization for oil finishes Solvent finishes would create an equal problem to the one you anticipate with linseed oil. The outside surface would evaporate its solvents first; how then would the interior solvents evaporate?
Remember that this is only an idea I have had. I have not tried or tested this methodology. I also cannot anticipate the equipment and precision of assembly with your system. I know for certain that I would use water only to test system safety. If you are unskilled in developing such systems, I would definitely recpmmend you consult with a knowledgeable professional.
>> I also think that paint pots have been more thoroughly tested
>> in finishing applications while pressure cookers have only
>> been tested for cooking.
Good point. I only mentioned the pressure cooker because you said the cost of the paint pot was a deterrent.
>> If the regulators failed the tool could explode;
I think a pressure relief valve would handle that. Maybe two if you're paranoid. But I agree that the possibility has be considered.
>> I do not know if oxygen is required in this scenario.
I don't know that it's required. I do know that partially filled cans of oil finish form a skin if you don't do something to exclude oxygen from the surface. That's why they sell little spray cans of inert gas to spray in your finish cans just before you close them. I assumed the oxygen is required for polymerization because I can't imagine it just being a catalyst.
Edited 5/7/2002 9:14:04 AM ET by UNCLEDUNC
". . . use pressure cookers to make Slivivitz (excuse my spelling but I was drinking some of this Plum based white lightning when I was also learning how to spell it. Alas the drinking somehow took presidence)."
You can say that again, er, I mean you can say precedence again.
^o^
(P.S. I went to the other Orygun--the one down in Eugene)
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