Problem with finish over cocobolo and rosewood inlay desktop

[r. mcelhaney]

I have just finished a contempory maple desktop (for my office) that has inlays of ebony, cocobolo, rosewood, and a few other exotic woods. I use my current desktop to write on, I put drinks on it, and I do some engineering drawings by hand, i.e., the old fashion way. So, I need a smooth hard top - one that I can work on every day. I have always liked the "soft" richness of an oil finish and I have had sucess in the past with using Homer's tung oil finish, waiting till it dries and then applying polyurethane over it. I have also used an oil finish followed by waxing, but I don't think that a wax finish has the hardness or eveness of a poly and a wax finish typically discolors when you forget and leave a drink on it.

Anyway, I did exactly what I mentioned - an oil finish followed by polyurethane. The cocobolo and rosewood did not like this at all (the poly wouldn't dry and the grain even seemed to raise on the rosewood). So, I stripped that off and tried Miniwax's sanding sealer before the poly. Still no luck. So I sanded back down to bare wood and I am back to square one. (By the way the bottom of the desktop which had no exotic woods, finished perfectly - so I know my finishing approach is sound for maple).

So, now I am thinking about re-doing the tung oil finish followed by Bulls Eye Dewaxed Shellac followed by poly. What are everyone's comments on this approach? Again, it's that cocobolo and rosewood (very oily woods) which are giving me the problems. Note, I will be sure and wipe both the cocobolo and the rosewood with denatured alcohol (the solvent in shellac) before I apply. Any other suggestions?

Thanks for everybody's time

[Leon]

Snip

I do not think the type of wood is gong to have any effect on whether the finish dries or not. That is all controlled by the climate in your shop.

[jds]

The oil in cocobolo will prevent curing of solvent based finishes -- even if wiped down with alchohol or acetone prior to applying the finish. Water based poly's and lacquers solve this problem.

Hope this helps.

[Leon]

Humm maybe slow down but not prevent. I have several pieces of furniture with cocobolo that I used only solvent based finishes on.

[James T. Kirby]

Yes, that reply didn't sound right. Luthiers have to do solvent finishes over cocobola frequently.

Perhaps a thin shellac wash coat as a sealer prior to the solvent finish?

JK

[jds]

Let's put it this way -- after wiping cocobolo down with acetone covering with one coat of wipe on poly and keeping the finished piece in a room controlled to 35% humidity and 85 degrees fahrenheit for 6 weeks the finish is still tacky enough to leave fingerprints when picked up -- so maybe it doesn't prevent curing -- but this is definitely what I would call excessively slow cure!!

[Leon]

Could very easily be the finish you are using. I waited a day or so.

[ted harris]

Horse puckey! I paint cocobolo with solvent based finishes everday, and it dries in the same amount of time as any wood it is over. Perhaps your finish is bad.

[Nova]

How long did you wait after applying the tung oil finish before applying the poly?

Poly dries in two stages. First the solvents evaporate and then it reacts with oxygen to cure. If the oil wasn't fully cured before the poly was applied I suspect the poly may have skimmed over at the surface level, sealing in the uncured oil and leaving a sticky mess. The problem would show up more in the denser woods that don't readily absorb the oil.

-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)

[jds]

Mr. Harris:

The same finish used on the cocobolo dries in the same conditions on maple, birch, oak in less than two hours. (I use enough of this to buy it in cases) After spending time talking to reps of Minwax and Rustoleum as well as other craftspersons that have experienced similar problems maybe you could be so kind as to tell us of the type and name of the solvent based products you use so successfully and how you apply them so that those of us not so fortunate could be enlightened.

[Leon]

General Finishes works just fine, Minwax may be your problem.

[jds]

Are you using the SealACell first and then applying one of the Arm-R-Seal polyurethanes? The Wipe on Poly I use is from Watco. Cocobolo is always a problem and I've had similar problems finishing Morado at times as well as some types of Rosewood. With the exception of these three wood types I have good success finishing some 30 other hardwoods so you're experience would be appreciated. When using Cocobolo and Padauk inlays I have had some success spraying a light coat of laquer as a sealer to prevent these woods from bleeding into the surrounding areas prior to trying to apply a total lacquer finish. I have had good luck on the "problem woods" mentioned with water based poly but would prefer a finish that does not develop the "plastic film" of the water based product.

[Leon]

Actually it was Prelude by General Finishes. I used Prelude back in the early 80's I shwitched to the Seal a Cell and Arm R Seal a few years ago.

The Wipe on Poly I use is from Watco. Cocobolo is always a

I wonder if the Watco finish is the progblem. I have heard numerous complaints about it taking weeks and weeks to dry expecially with the oils.

[ted harris]

Sherwin Williams conversion varnish works fine. Currently I am using an automotive clearcoat, DuPont Chromaclear HC 7600S, and it is sprayed on. Perhaps you should look into a more industrialized finish, rather than a "Harry homeowner" finish. I just wouldn't depend on Minwax or Rustoleum, a product that sells for $2.99 at the local hardware store. Ever hear that saying, "you get what you pay for?" If you are indeed buying your finishes by the case, then you are using far more than I am. So pricing should not be an issue for you. There are tons of other finishes out there that will work great for different appilications.