Replies

1. 
   SgianDubh | Jul 18, 2003 04:42am | #1

   That's part of the the answer, stu. Another good reason is that wiping down with mineral spirits gives you the chance to look over the project and spot and correct faults prior to applying a polish of some sort. Polish will also reveal any such faults, but at that point you'd probably need to strip the polish to make the repair.

   For example, a wipe over with mineral spirits (or naphtha, lacquer thinner, etc.,) might reveal some glue that you've failed to remove, an oily spot, or a scratch across the grain, etc., which can be fixed once the solvent has evaporated. Slainte.

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1. 
   Kevin | Jul 18, 2003 07:58am | #2

   For example, a wipe over with mineral spirits (or naphtha, lacquer thinner, etc.,) might reveal some glue that you've failed to remove, an oily spot, or a scratch across the grain, etc., which can be fixed once the solvent has evaporated.

   'Tis true. However, that is usually done before the sanding sealer is applied. Sanding sealer will reveal all of those things too... before it is sanded of course. But, at that point it's a bit late for fixing some of those problems. Also, I would strongly recommend NOT using lacquer thinner to wipe down sanding sealer. It will either dissolve or ruin most sealers.

   The main reason for using mineral spirits to wipe down sanding sealer before applying the final finish is to remove all of the sealer dust and other particals. This is critical with most any type of sanding sealer other than solvent-based lacquer sanding sealer and shellac, which are going to be top coated with a like product. With nitro lacquer, acrylic lacquer, shellac and variations based on one or more of those resins, the solvent(s) in the top coat will dissolve any nitro lacquer or shellac sealer dust one may have missed and melt it back into the surface. But with almost every other sealer/top coat combination out there, the top coat solvents will not dissolve any sanding dust left behind because once the sealer has dried it won't reliquify. So, wiping the sealer down with something like mineral spirits can be critical to both the final appearance as well as for adhesion between the top coat and the sealer coat.

   Regards,

   Kevin

   Edited 7/18/2003 1:02:11 AM ET by Kevin

1. 
   SgianDubh | Jul 18, 2003 08:23am | #3

   Fair point, Kevin. It hadn't occurred to me that I was being unclear. I was including sanding sealer as part of the final polishing procedure, and I meant to say clearly that the wiping down with mineral spirits (or naphtha, lacquer thinner, etc.,)  to check for faults be done before the application of any film polish, i.e., on bare wood, unstained, undyed, unpolished, etc.. As you say, you can wipe dust off between coats of polish too, but it wouldn't be a good move to wipe down an oil varnish or shellac with lacquer thinner, ha, ha. Slainte.<p href="http://r-gjones.laof.home.att.net/&quot; Website               

1. 
   Kevin | Jul 18, 2003 09:10am | #4

   Oops... my bad! I misread Stu's post. I thought he was saying that the Minwax can said to wipe down the sanding sealer with mineral spirits after the sealer is sanded. LOL

   Carry on. You're doin' just fine.

   Chagrined,

   Kevin

2. 
   stubert | Jul 18, 2003 01:35pm | #5

   Thanks Sqian Dubh and Kevin!

   After the the sander/sealer I am finishing with several coats of Minwax Waterbased Polycrylic. Kevin, do  I hear you correctly, in that as long as the mineral spirits doesn't break down the finish, I could wipe the project after each round of sanding?

   StuStuhttp://www.stubert.funtigo.com

1. 
   SgianDubh | Jul 18, 2003 05:42pm | #6

   Stu, Kevin hasn't replied yet, so I'll jump in. Yes you can wipe down between coats to remove sanding dust with a solvent that doesn't dissolve the existing polish. In other words, you wouldn't wipe down between coats of shellac with alcohol, which is shellac's solvent-- you wouldn't use lacquer thinner either. And you wouldn't wipe down pre-catalysed lacquer with its solvent, lacquer thinner, but you might use a cloth slightly dampened with mineral spirits or naphtha..

   With the water based polish (varnish) you are using avoid using stearated abrasives when lightly sanding between the coats-- the fat/grease element in the stearate can cause adhesion problems with subsequent coats. You will probably find a note on the can giving similar advice.

   Polishes are often tack ragged between coats to remove any stray foreign matter and sanding dust, and again the use of tack rags are best avoided in your specific case because there is an element of greasiness to them. Instead of tack rags, I'll often drop a cloth in clean water, ring it out thoroughly, and wipe down with this between coats. I let this dry and follow up with a lint free dry cloth. I often use this between coats of oil varnish, and between sprayed lacquers of the nitro-cellulose family--- and shellac, which I don't use much of, is also surprisingly tolerant of a water damp rag being passed quickly over it, although on shellac I tend to use a tack rag. Now that I've completely confused you, I hope all is clear, ha, ha. Slainte.<p href="http://r-gjones.laof.home.att.net/&quot; Website               

2. 
   Kevin | Jul 18, 2003 10:58pm | #8

   Kevin, do  I hear you correctly, in that as long as the mineral spirits doesn't break down the finish, I could wipe the project after each round of sanding?

   Yes.

   Ditto what Squin posted. Plus, mineral spirits won't break down any finish that I'm aware of. That's probably why it's used so widely for wiping off dust and stuff like that. It is a fairly decent wax and grease remover, though. Naptha's better... but, Mineral Spirits works too.

   Personally, I'm a lot less hesitant about using a tack cloth between coats of polyurethane. I know lots of guys who tack before spraying poly and who have no problems. The trick is to use a light touch so that you're not leaving any residue from the tack cloth behind. I used to paint in a sheet metal shop years ago where all the stuff that got painted was coated with an industrial polyurethane (Polane). We were under ISO 5000 at the time and a certain percentage of everything painted was pulled aside and adhesion tested per the ISO requirements. We never had any failures due to using tack clothes.

   That said... it's almost always best to err on the side of caution. Avoiding the use of tack clothes certainly won't cause you any problems.

   Regards,

   Kevin

   Edited 7/18/2003 6:28:28 PM ET by Kevin

3. 
   Paul_Snyder | Jul 19, 2003 01:46am | #9

   Don't use mineral spirits to remove the dust between coats of waterborne finish. Minseal spirits should not harm the finish but it will leave a slight oil residue that impedes adhesion between coats (of waterborne). Instead, use a cloth slightly dampened with water. That makes a good "tack cloth" for waterborne finishes.

   Paul

2. 
   HowardAcheson | Jul 18, 2003 07:40pm | #7

   A participant on Wood Magazine's finishing forum sent a letter to Minwax asking them the benefits and cautions of use the Minwax Sanding Sealer. Also asked was whether the product contained any stearates. Here is the responce from Minwax.

   **********

   There are neither technical or practical advantages or disadvantages to the use of Minwax Sanding Sealer. It is designed for use as a sealer coat under Minwax Fast-Drying Polyurethane. Because of this, Minwax Sanding Sealer contains no stearates of any kind. It functions as a very good sealer for our polyurethane for those who like to use Sealers.

   There are no stearate-containing sealers acceptable for use under any oil-based polyurethane. Stearates will negatively affect the adhesion properties of all urethanes.

   Sanding Sealer resin must be compatible with it's top coat resin to have good adhesion. The Minwax Sealer was formulated specifically for the Fast Drying Polyurethane and may not be compatible with other brands or other types of finishes.

   You cited that "professional opinions" that thinning polyurethane impoves adhesion. If this means "better than stearate containing sealer", then you are technically correct. Stearates will make urethane peel, and thinned polyurethane won't.

   The percent solids composition of polyurethane is regulated by the EPA persuant to Section = 183(e) of the Clean Air Act. The only comment the regulation allows is: Thinning is not recommended.

   **************

   I think their first sentence may be the most honest assessment that any company ever gave about the need or usefulness of their own product. The final sentence in the first paragraph sums it up. It satifies a marketing need for some who think that sealers have some benefit.

   The product is not designed for use under waterborne finishes as far as I can determine. If used, sanding sealers should be matched to the final finishing product.

   I tried some and it doesn't seem to sand any easier than plain, old thinned varnish. So if it doesn't contain stearates to help it sand easier and it, in fact, doesn't sand easier, why do they call it a "sanding sealer"?

   
   

   ---

   Edited 7/18/2003 12:43:44 PM ET by Howie

1. 
   stubert | Jul 19, 2003 04:13pm | #10

   Thanks to all for the great wealth of informaton and feedback. I gotta tell ya this sander sealer has been big fat failure. Put it on yesterday, let it dry as directed. Sanding with 120 girt as directed provided just horrible results. What began as a beautifully prepared project--surfaces smooth planed, scraped, and lightly sanded is now a mess.  I'll be spending the day sanding this crap off the piece :(Stuhttp://www.stubert.funtigo.com

1. 
   Kevin | Jul 19, 2003 08:16pm | #11

   Wow... 120 grit to sand sealer? Am I the only one who thinks that's more than slightly insane? Personally, I would never, ever use anything courser than 220 on any type of wood sealer. For that matter, I've never seen a manufactorer recommend anything courser than 220 for scuff sanding sealer. In the last couple years I've taken to using 320 grit exclusively for scuff sanding and am very pleased with the results. Sure it doesn't take it down quite as fast as 220. But, for that same reason it also doesn't burn thru nearly as easily and... it leaves a much smoother surface. On something where there is only one coat of sealer and one coat of finish on top of the sealer, for that "close to the wood" look, I can really notice the difference between using 220 vs. using 320. The 320 produces a VERY silky smooth finished surface.

   Regards,

   Kevin

1. 
   HowardAcheson | Jul 20, 2003 08:58pm | #12

   Yeah, I missed that. 120 makes no sense. Perhaps it is a mistype. 320 is what I would use, if I used sanding sealer. I use 320 to flatten the first coat of finish and 400 for between coat scuffing, if necessary. 120 will leave a very visiable scratch pattern.