Finishing and Refinishing

[wayne136]

I built a desk out of quarter sawn oak. After staining it with an oil-based stain (and letting it dry for 2 weeks), I applied a coat of oi-basded polyurethane. As the finish was drying, the desk started to develop a fuzzy white film in many areas. This haze actually started to appear after the stain was applied, but an extra coat of stain made it go away. It came back a lot worse after the poly was applied.

I live in a dry climate (Arizona), and the stain was was given plenty of time to dry after both coats. The stain and poly was both purchased recently. I've used these same products on other furniture pieces (different wood species), but have never seen this before.

Does anyone know what this could be, or how to get rid of it?  Thank you!

[amateur60]

What brands and exact names on the labels were the products you used?  Sometimes things aren't always quite as they seem with finishing materials since marketing departments seem to write the labels and directions without much if any input from the technical side.  (same questions as for Al) 

[wayne136]

Thanks for your response!

Both products were Minwax. The stain was "Wood Finish, Penetrates, Stains & Seals. Natural 209". The back of the can says "Minwax Wood Finish is an oil-based wood stain which provides long-lasting wood tone color." The poly was "Fast-Drying Polyurethane. Superior Durability. Clear Semi-gloss." The back of the can says "Minwax Fast-Drying Polyurethane is a clear, oil-based, durabel protective finish."

I've used both products (together) before, without any problems.

[amateur60]

Well, I'm perplexed.   The Minwax "natural" isn't really a stain, it's a super dilute varnish that's the base for their similarly labeled products that do contain pigment and/or dye to make them actual stains.  It would play no real roll in the appearance of the final product.  But it seems clear that there was a problem with this particular batch and how it interacted with the wood of your desk since you got some of the frost even before you applied the more concentrated varnish over it. 

Grasping at various straws.  The desk was new wood?  Did you use any sort of tack cloth?  How did you sand it, and with which sand paper?  Were there any other chemicals in the enviroment of your finishing space? 

[Howard Acheson]

Did you follow the directions on the can of stain to wipe off the excess after letting it set for 15-20 minutes?

What was the temperature and humidity when you applied the finishes?

[wayne136]

The wood was new, in that I bought it recently from a reliable supplier (Woodworker's Source) that's been providing great lumber to me for years. I didn't use any tack cloth. The sandpaper I used was the "gator" brand, progressing through 80/120/220/320 grits. Chemicals... I did try a cutch extract/potasium dichromate finsih on another project recently, but the desk wasn't in the finshing area when I tried that.

[wayne136]

Yes, I'm kind of "monkish" about following directions. Like I said before, I've used this combination of stain/poly successfully before. In fact, I applied this finish to some coin boxes (different wood) within a day or so of applying it to the desk. The temperature in my shop was around 80 degrees, and the humidy was low, as it usually is around this season in Arizona.

[Steve Mickley]

Wayne;

First, is the oak red oak or white oak?  It is difficult to tell from the photos.  Second, you describe this interesting condition as "...a fuzzy white film...".  The white part is obvious, but "fuzzy" and "film" suggests something on the surface that is: 1) a film that can be removed by scraping, and 2) has a "fuzzy" physical characteristic.  Is this accurate, or is the white what-ever-it-is contained within the finish, or possible associated with the surface of the wood beneath the finish?

Also, Wayne, you say the temperature in your shop was around 80-degrees and that the humidity was low.  I am not questioning that; but, was the finish applied in the early A.M.?  Further, is the shop constantly air-conditioned?  If not, do you recall the conditions the night before you applied the finish?

 Steve

[wayne136]

The wood is white oak. I used a bad choice of words. The white stuff seems to be under the finish, as I first noticed it when I was applying the stain. I ignorantly just applied another coat of stain, thinking that maybe the wood had "dry spots" or something that caused the stain to be absorbed in a strange way. The white areas seemed to go away after the second coat of stain. After waiting 2 weeks for the stain to dry, I applied the poly. The next morning, the white stuff was back, much worse than after the first application of the stain. It doesn't seem to be on the exterior of the finish.

I applied the stain around lunchtime (noon). My shop isn't air conditioned, and the night before I applied the stain it was cool (in the 60s), but warmer in my shop, which is well insulated.

Do you think I should just strip the desk and try a different stain/finish? If so, what method of striping do you recommend? I'm trying to stay with a mission appearance, so can you also recommend a good stain/finish combination that would fit that?

Thank you, everyone, for responding to my mystery!

[Steve Mickley]

Wayne;

...and I'm not sure I have an answer; but, I will tell you what I think may be going on.  First of all, to echo something Amateur60 pointed out earlier in this thread, you have not applied any "stain".  Minwax "natural" stain is little more than a very weak wiping varnish; a mixture of varnish and thinner.  It may contain a bit of dye to slightly amber the wood, but if it does the amount of dye is very small.  It contains absolutely no pigment.  Therefore, the finish you have actually applied consists of two coats of highly thinned wiping varnish followed by one coat of polyoneverythane.  Note: There is nothing wrong with this schedule (with the possible exception of the poly); but, for future reference if you simply thin the first coat of varnish in a ratio of 1-part varnish to 3-parts thinner you will obtain the very same result without the expense of purchasing a deceptively labeled second product.

At any rate, back to the white film; my best guess is that you are dealing with an issue of moisture in your finish that has come about for one of two reasons, possibly a combination of both.  I realize that Arizona is quite "dry", but it isn't totally dry and moisture problems arise due to relative humidity, not the level of humidity.  It takes very little actual water vapor trapped within a finish to create the problem you have experienced.  Here is the scenario that I suspect has produced the problem:

Let's begin with the white oak itself.  White oak is not native to Arizona.  It is harvested in the mid-west, milled into lumber, dried, and shipped to Arizona.  In the areas of the country where white oak is harvested and milled into lumber the typical Equilibrium Moisture Content (EMC) of hardwoods is 10% to 12%.  EMC is the moisture content to which wood can be air-dried, or the MC at which kiln-dried lumber will stabilize in an unconditioned environment.  By comparison, the EMC in your region of the country is 5% to 7%.  The importance of this is that lumber you bring into your shop that has not "acclimated" to local conditions may be relatively "wet" if it was sufficiently exposed to normal atmospheric conditions at its point of origin.  If kiln-dried to 6% to 8% MC the MC may have increased during storage after drying.  Even in a best case storage and shipping scenario, lumber kiln-dried to 8% will have a moisture content 2% to 3% higher than the EMC in your area.

Now, contributing factor two; your shop is not conditioned, therefore as the temperature rises and falls the relative humidity will fluctuate even though the actual humidity is quite low.  Relative humidity is a function of moisture content in the air and air temperature.  At cooler temperatures the air can hold less water-vapor than it can hold at warmer temperatures.  While the temperature of your shop is important, the temperature at the surface being finished is far more important.  Wood takes longer to come to room temperature than does the air in the room.  Well insulated or not, it is quite possible that the temperature of the white oak at noon was actually lower than the air temperature in your shop.  Now, add to this temperature difference the cooling that took place at the surface of the wood as the thinner in the thinned varnish (what Minwax calls "natural stain") evaporated and you have created a condition in which, even in Arizona, the air at the surface cooled by evaporation can no longer hold the moisture in the air.  This same evaporation/cooling sequence could draw excess (relative) moisture from the wood if the moisture content of the un-acclimated wood was above the EMC.

Why did the "cloud" go away when the second coat of "stain" was applied?  Because the so-called "stain" contains very little varnish; it is mostly thinner.  So, when the second coat was applied, much like applying lacquer thinner to "blush" in a lacquer finish, the moisture was released.  If the dew point was higher at the time of the second application the cloud would not have reappeared.  When the Minwax "Fast Drying" poly was applied the conditions that created the problem in the first place returned, probably aggravated by the high volatility thinners used by Minwax to make their DIY poly "dry fast".  (May I suggest that "fast" is not always good?  Might I even suggest that "fast", while attractive in the DIY market is not such a good idea when a quality finish is the objective?)

Do I think you should strip the finish and begin again?  Yes, using a stripper that contains methylene chloride; follow the directions on the can.  As far as the new finish is concerned; please consider the following for the "Mission" look.  Begin with water-soluble dye in the light fumed oak "color".  This will simulate the look of fumed white oak.  "Seal" the dye with a coat of super blonde shellac mixed in a two-pound cut.  Lightly sand the shellac when dry with 320P, sand just enough to smooth the surface.  Then, apply a dark heavy bodied gel stain such as General Finishes Java.  Work the stain into the open grain of the oak and then wipe away all of the excess stain that is not in the pores (the objective is to simulate the lamp black wax used by Mission builders).  Finally, apply two or three coats of non-poly varnish.  My preference would be Pratt & Lambert #38 in the satin sheen.

I apologize for the tardy reply; I have been away from internet service for a few days.  As I said, this represents my best guess.  But, I believe it to be a reasonable explanation for your problem...

Steve