Finishing question - pin holes in second coat

I put the first coat of poly on my desktop and it looked fine. Here are the facts pertinent or not:
1. Thinned about 10% with Low odor Mineral spirits from HD. - Minwhacks poly. 2. Applied at 66 degrees with 8# pressure HVLP .041 tip. 3. Looked fine and dried enough in 4 hours to sand lightly with 220 grit, per instructions on poly. 4. Wiped off surface with mineral spirits (damp) and wiped again with dry rag. 5. Applied second coat with same parameters as above.
On the first 3 pieces I sprayed, there were obvious little pinholes in the film that weren't there during the first coat.
QUESTIONS:    
I'm sort of suspecting the sandpaper. It is Norton's new line of 3X 220 grit. It's yellow and very flexible. Even though it says it's for between coat sanding, I'm wondering if it has sterates in it. It says nothing about sterates, but wouldn't that cause pinholes in poly?
I JUST WENT TO THEIR WEB SITE AND FOUND OUT THERE ARE STERATES IN IT. WILL THAT SCREW UP THE FINISH??
Oddly, the last thing I sprayed was the desk top and it didn't look like it had pinholes in it. I sprayed a bit onto scrap before spraying the project, in order to set the spray pattern and volume. Even so, COULD poor mixing of poly and thinner in the gun cause the first few items to have pinholes? I resprayed them again and still could see pinholes.
What do you think went wrong?
Can I fix this for the next coat by using naptha or some other solvent as a final wipe instead of mineral spirits?? What solvents would be safe and effective for between coats?
dave
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I have included a post from 1997 that may be useful for this and other finishing problems. Specifically, the pre-fill in number 6 applies to timbers such as oak, which, IIRC, is what your desk is made from.
I would be surprised if Nortons sold a paper that affect finishing after sanding (not saying it's impossible, just unlikely) and suggest you look at other possible causes first.
Greg
From: ersatz name ( snipped-for-privacy@hotmail.com) Subject: Factory Furniture Finishing (LONG POST!) Newsgroups: rec.woodworking Date: 1997/08/21
I am not the author of this information. I did edited it somewhat. This information comes from one of the big makers of furniture that you can buy in the stores.
This is what, how and why they do what they do in the furniture factories. Many of the phrases and jargon will become more comprehensible as you continue to plow through this outline.
I find this inside look at the furniture industry fascinating. I have not seen ot printed or posted elsewhere. I hope that it helps to instill a greater appreciation of the new furniture that you see in the stores in all of you who care to read this. Also, I hope that this information is useful, and at very least interesting. ----------------------------------------------------------------
1. EQUALIZING
Objective: To reduce color intensity of varied woods.
Due to various reasons (price, seasoning, drying, etc.) all woods entering finishing rooms are not the same color. Any abnormal color in the wood must be neutralized. Example: a green pigmented type material to tone down the redder woods and a yellow orange toner to tone down the blue, gray and darker woods.
This operator generally spends half of his/her time looking, and the other half spraying. Equalizing is a judgmental process and special care should be taken in training this person. Improper application can result in a wider variation in color within individual pieces, rather than a general blend. Poor application can also result in a painted appearance. ----------------------------------------------------------------
2. SAP STAIN
Objective: To bring varied colored woods to an overall average color.
Sap stain is generally used used on the lighter wood to bring it closer in color to the average. In many cases, special saps are needed to blend various species of wood together in the same piece of furniture.
Care should be taken in this operation so as not to undo what the equalizers have accomplished. Again, the spray operator need not spend a majority of his/her time spraying, but rather spend more time in being effectively selective.
Following correct equalization and sapping operations, a piece of furniture should blend better as far as overall appearance and color. ----------------------------------------------------------------
3. OVERALL BODY STAIN
Objective: Establish undertone color.
Consistent stain application is of utmost importance. Care should be taken to insure that the operator has sufficient time to apply a good uniform coat of stain. Each piece should receive a good uniform wet coat of body stain.
Comment: more off color furniture can be traced to above operations than any other in system. It is imperative to have good step panels at these operations. ----------------------------------------------------------------
4. WASHCOAT
Objective: Seal off stain and provide smooth base (after sanding) for subsequent operation. Consistent spray procedures are essential in this operation.
A close check on washcoat should be kept as any change in white wood sanding or bad spray technique will effect the bite of the wipe.
Special consideration should be given to turnings and end grain. These may be sealed with a sealer before or after washcoat. This is most important on soft[er] woods such as pine and maple. Care should be taken to prevent spraying material on surfaces that do not require it. This causes clean light areas where the wipe coat does not bite sufficiently. ----------------------------------------------------------------
5. WASHCOAT SANDING
Objective: To prepare surface for finish wipe coat operation.
This step is important since it is the first finishing operation leading to a good build and smoothness in the final film. Sufficient sanders should be provided to insure smooth surface. If this operation goes through rough it not only effects color but also makes sealer appear rough and needing more sanding. ----------------------------------------------------------------
6. PRE-FILL
Open grain woods (oak, pecan, etc.) should be pre-filled with a paste filler mixture to fill the pore. This operation helps the rub room rub the tops to a uniform flat surface, rather than being open and hungry. The actual application is usually done with a brush, rag, or a sponge. Once filler is applied, it needs to be forced into the pore with a circular motion using a pad wheel. This operation will prevent pinholes when done properly. ----------------------------------------------------------------
7. INERT GLAZE
Objective: To provide a cleaner more uniform finish.
This material is applied selectively to areas where the fill glaze might "bite in" and cause darkness and/or dirtiness. Once again, care should be taken to apply this only to those areas that need it (end grain, turnings, etc.). Careless application will result in unwanted lightness in areas that did not need inert. ----------------------------------------------------------------
8. FILL GLAZE
Objective: To provide color and depth to finish.
With correct sanding and washcoat application the first wipe can generally be wiped fairly clean. The first wipers generally break the wipe down and work in, into the pore. These same people can also help prevent black turnings and end grain by giving them attention first. Generally speaking, tops should be wiped last.
The next wipers will finish cleaning up the cases. Many times a glaze brush will help remove excess material from cracks, grooves, and corners. This also adds a blending affect. This is a good time for an inspector to make sure that all fill glaze is wiped evenly and removed properly. ----------------------------------------------------------------
9. HIGHLIGHTING OF WIPE COAT
Objective: To enhance the grain of the wood and design features.
Highlighters should be aware of any special effects needed for the particular piece of furniture such as wearing of corners, etc. At times sandpaper is needed for depth of highlight, at other times steelwool will give a softer look. Care should be taken not to pull filler out of the pore on open grain wood with steelwool.
Again, it is important to compare highlighting techniques. Highlighters should look for interest areas in the wood and bring these out; knots, cathedrals, crossfire, dark moldings, etc. Wear highlighting is more pleasing to the eye, but finger highlighting is easiest, therefore, for the best appearance wear highlighting should be used. It is important to compare highlighting techniques in production to those on the color sample. ----------------------------------------------------------------
10. SEALER
Objective: To prepare surface for topcoats.
Sealers are higher in solids than washcoats Good sealer application means a good foundation for topcoats. Good spray techniques and sealer flow are imperative. ----------------------------------------------------------------
11. SEALER SANDING
Objective: To prepare antiquing and dimension to finish.
This operation is very important as it will determine how smooth and clean the glaze operation will be. Poor sanding leads to dark and dirty "bite in" areas in glaze operation. Good sanding leads to good lay down and flow of lacquer.
The importance of washcoat and sealer sanding is the most overlooked and taken for granted areas in finishing in the furniture industry today. ----------------------------------------------------------------
12. SECOND GLAZE
Objective: To provide uniform color and depth to finish.
The second glaze should be wiped uniformly and brush blended to give an overall uniform and pleasing appearance. ----------------------------------------------------------------
13. HIGHLIGHTING OF SECOND GLAZE
Should be done with steelwool to enhance grain of wood and design features and give overall pleasing appearance. Special clean-up may be needed to avoid any dark areas that detract from finish. ----------------------------------------------------------------
14. FIRST LACQUER
(see #18 TOPCOAT LACQUER) ----------------------------------------------------------------
15. SPRAY PAD
Objective: To provide color and depth in an aesthetic manner.
Pad stain should be sprayed uniformly like a body stain. The spray pad is then mottled or highlighted with a damp alcohol rag for desired depth of finish and to match approved color sample. ----------------------------------------------------------------
16. HAND PAD AND BURNISHING
Objective: To further enhance the grain and provide further aesthetic value to the finish.
Hand pad is applied by hand with a rag shaped in the form of a fine pad. The rag is wet to the proper degree and the stain is then applied selectively to those areas to which it can be most advantageously done. If this operation is to be of any benefit, it must be done by trained and motivated personnel. This operation properly done will provide the most beneficial aesthetic quality to the finish of any operations. Also, if proper highlighting techniques are used in first wipe and spray pad, much less pad is needed. ----------------------------------------------------------------
17. SHADE
Use as little as possible to uniform cases. Shade, like equalizer and sap, should be applied to selective areas only. ----------------------------------------------------------------
18. TOPCOAT LACQUER
Objective: To provide build, protection and to bring out the beauty of the wood and the finishing technique.
A. Air Spray: The fluid pressure and atomization pressure must be properly established to provide most efficient application in relation to product size, speed of conveyor and load. In addition, the proper tips and needles should be used.
B. Airless Spray: The fluid pressure, tip size and fan width should be coordinated to provide the most efficient application, according to the product size, speed of conveyor and load.
Dry time between coats and after final lacquer is critical to provide a well cured film. Should the film not be dried thoroughly, it can result in hazing of the finish either during rubbing or afterward. Insufficient curing will result in a drop in sheen after packing. Consequently your products may look good going into the box, but will be too low in sheen when opened at a later date. Also, insufficient curing will lead to paper printing in the box.
Your topcoat of lacquer should be formulated to give you maximum build and clarity. The build and smoothness of the topcoat adds considerably to the clarity and brightness of the finish. ----------------------------------------------------------------
19. RUBBING
Objective: To obtain smooth feel and proper patina to enhance the finish.
There are a multitude of rubbing options that can be used depending upon the desired results. Listed below are the general principals or choices involved:
A. The drier the lacquer film is, the cleaner and more stable will be the final rub job.
B. The rubbing lubricant to use should be a vegetable oil as opposed to petroleum.
c. Depending on the sheen and clarity desired the sandpaper used should be in gradations so that each succeeding finer grit can remove the scratches of the proceeding one, i.e., 400 followed by 500 rather than 600. Also the finer grit you use the clearer will be your rub job.
D. Rubbing lubricant (even when using vegetable oil) should be kept cleaned off the lacquer surface as much as possible to keep them from permeating the lacquer film and then "blooming" back later causing a haze.
E. Following cut down with lubricant and sandpaper there are a variety of materials to use to uniform the sheen depending upon how high a sheen you want. They are as follows:
Ultra-fine Scotchbrite 4/0 steelwool Rottenstone and vegetable oil Rubbing compound and buffing wheel Rubbing compound and scotchbrite
F. After the above operation, the surface should be cleaned and/or waxed with a soft cloth. (Do not use waste).
Good rubbing procedure is essential to producing quality looking furniture. A good finish is just like any other craft, it depends upon good workmanship throughout the entire process, beginning with the most important process, good white wood sanding, which provides a good foundation for the finish. -------  Daniel
NOTE: Send me your e-mail at "shafner at webspan dot net" taking out the quotation marks and inserting the appropriate symbols.
/ `-' ) ,,, | IU U||||||||[:::] \_.-.( '''
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Hi BAD, I did a lot of reading when I first bought my sprayer and all though I never experienced it in person, one author mentioned "Micro bubbles" in poly. These would be caused by shaking not stirring the mix and would result in pinholes. IMHO this James Bond kind on thinking is bull but then I have been wrong before. Cheers, JG
Bay Area Dave wrote:

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It would seem to me that atomization would free any entrapped air.

result
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Yes, George, the symptom is NOT like entrapped air which is what I get if I brush unthinned poly.
dave
George wrote:

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So, as another suggested, you may have the porous oak blowing bubbles from below. Put the magnifier to it to see if the pinholes have a pore below 'em?.

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I didn't shake the can or the spray cup; I poured the poly from the original can into the cup, added a bit of thinner and swirled them together (only about 2" of material so it was easy to swirl). The finish doesn't look like it has bubbles in it like when I've used straight poly with a brush. That method always used to leave a lot of entrapped air. This issue with the second coat of "pinholes" are very tiny pin prick sized depressions with no surrounding gentle depressions. AND of the 4 drawer fronts I sprayed, the first two were the worst, the third is so-so, the fourth looks really good, and so does the desk top which I sprayed after doing the drawers.
dave
JGS wrote:

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