Replies

1. 
   AzDiscDog | Apr 26, 2007 12:28am | #1

   Hey Toolman,

   I've used lots of poly, but I usually brush it on instead of spraying. That (obviously) gives me a thicker layer to start with. My first guess is that you don't have a thick enough layer of poly down yet, so you're losing the shine with the sanding. I generally do two or three coats of brushed poly depending upon the project and use factors. I've never been satisfied with just a single coat, especially not after a light knock-down sanding.

   Generally, I use either 220 or 400 for my follow up sanding and clean up the dust with a damp cloth or tack cloth.

   In short -- give it a few more coats and see what happens.

   As you're time constrained, I would take a look at the directions and see how soon you can apply subsequent coats. Offhand, I'm guessing you'll need at least three coats.

   Glen

1. 
   toolman50 | Apr 26, 2007 12:43am | #2

   Thanks for responding, Glen.

   This is my second coat and I sprayed it on pretty thick.  My first coat wasn't all that thick, but thick enough I didn't have any trouble sanding through it.  I didn't sand this coat, I rubbed it down lightly with steel wool and tried to bring the luster back with mineral spirits.

   Do you use a dry or wet sandpaper, or does it make any difference?

   Toolman

1. 
   AzDiscDog | Apr 26, 2007 01:09am | #3

   Hi Toolman,I use dry sandpaper, but mostly because I'm lazy and haven't taken the time to play around with wet finishing techniques. I have always equated wet finishing with a french finish, and things in my house are too crazy to put that much time into a finish only to have it ruined shortly after coming into the house. :-)And wet vs. dry probably does make a difference as having a slurry on the surface will change how the grit bites into the finish. But that's about all I can postulate on that one!I thought a little more about the problem based upon the additional info you gave, and I have a couple of other thoughts.Poly probably has a different luster than lacquer, so what's listed as "semi-gloss" for one may or may not provide a comparable sheen using a different finishing material.And for that matter, poly luster varies considerably from brand to brand, even when they claim "gloss". Check out FWW 178, starting at pg 32. There's a pretty good article comparing a variety of wipe-on finishes. His "sheen" category reflects the measured sheen of the finish, not necessarily what the can said.Unfortunately, the article didn't include lacquer for comparison, so I can't immediately answer my hunch that you may have different expectations from lacquer than the results you'll see with poly.I really can't see the mineral spirits as damaging the poly coats you've put down. The stuff is renowned for its toughness. However, I can't completely rule it out as the coat would be pretty fresh and would not have fully cured. Fully dried, yes, but not necessarily fully cured. I'm having a harder time with this theory, but I'll throw it out there.Does the piece have the degree of gloss you want prior to your light sanding with the steel wool & mineral spirits?You could always whip up a test stick and try a different method of touching up the finish. And I think I'm now a true knot-head as I was able to reference a back article of FWW.... woo-hoo!Glen

1. 
   toolman50 | Apr 26, 2007 02:50am | #4

   Thanks Glen,

   Good food for thought.  I'll dig out my FWW 178 and read that article again.  Since your first reply I've been looking my project over and I can't help but think I have enough poly on it.  I'm having trouble convincing myself that another coat would react any different to my process.

   Because of being short on time, and wanting as much time as possible for the finish to cure, I'm still trying to come up with a solution for smoothing that last coat without re-spraying.   I have some small dust specks and air bubbles that I would sure like to rub out.

   Prior to my attempt with the steel wool, the finish has definitely got a glossy shine to it.  In fact, it's looks more like a gloss than a semi-gloss to me.  I'd be pleased if I ended up with half the shine, as long as it was consistent.

   Toolman 

1. 
   AzDiscDog | Apr 26, 2007 05:00pm | #8

   Hey Toolman,Given what you said about the gloss prior to sanding, and based upon the replies from Howie & Blewcrowe, I think you have your answer.Given where you're at and that delivery is in potentially 72 hours, here's what I would do:
   sand out the bubbles & specks
   spray another coat of poly on the piece to get the gloss back.
   Let dry for 24 hours
   *Lightly* dry sand with 400 grit sandpaper.
   Wipe down with a damp cloth.I almost always use Min-wax, and 24 hours is usually plenty enough drying time. ZAP may have different characteristics.Best of luck!
   Glen

2. 
   blewcrowe | Apr 26, 2007 04:32pm | #7

   I really can't see the mineral spirits as damaging the poly coats you've put down. The stuff is renowned for its toughness. However, I can't completely rule it out as the coat would be pretty fresh and would not have fully cured................

   I encountered that problem early on and learned. You can wet sand with a solvent and really mess up a good finish if you hit it when it's dry but before its mostly cured.

   And yeah, full curing may take weeks, but my experience tells me its cured enough to work on after a week.

   Edited 4/26/2007 9:33 am ET by blewcrowe

1. 
   AzDiscDog | Apr 26, 2007 05:02pm | #9

   Hey Blewcrowe,Thanks for the advice. I didn't realize mineral spirits would react with the unfinished poly like that. Well, I think I expressed my skepticism pretty well earlier, so thanks for the education!So now I qualify as a 'true' knot-head for citing a FWW article AND my laziness has paid off. I'm gonna go out and buy a lottery ticket today.:-)Glen

2. 
   blewcrowe | Apr 26, 2007 05:29pm | #11

   Well, let me qualify that. I've largely given up using poly. My finish of preference in most cases are the Waterlox formulations, which share many similarities with and a couple differences from poly.

   (Note: I prefer the penetration properties and effects of Waterlox over poly, so I don't use poly much anymore. Takes longer to finish, but I like the results better. Just personal preference. If I'm making a box or cabinet, I'll use shellac on the interiors and Waterlox on the exteriors.)

   Anyway, with Waterlox, wet sand with naptha, turp or mineral spirits within three days of finish and you end up with a mess. Apparently the solvents in combination with the action of the grit can reactivate or expose uncured oil varnish type finishes. But I find that after seven days, I can usually go in and rub out without doing major damage.

3. 
   toolman50 | Apr 26, 2007 06:28pm | #12

   Thanks to everyone for all your advice/information.  I appreciate you sharing your knowledge and experience.  Now that I'm getting more serious about my woodworking I'm finding that building it is the easy part.  Being able to put on a good finish is an art of it's own.  It's nice to have a forum like this to get help from those much wiser in their craft than I.  I'm too old to learn it all by my own experiences.

   Toolman

4. 
   BigK | Apr 27, 2007 01:22pm | #13

   I have figured out a pretty good trick for finishing with poly. Generally because poly takes so long to dry it tends to catch dust, etc. and dry a little rough. For a final coat I will lightly sand and tack the last brushed coat and wipe on a coat of Old Master's Wiping Varnish. This is really a gelled oil poly that goes on real nice and will give you a real nice finish that feels glass smooth to the hand. This product dries in 2 hours and is really easy to use.

5. 
   blewcrowe | Apr 27, 2007 05:44pm | #14

   Another trick I've used is to thin my last apps with naptha. Naptha helps it dry fast. I'll do a coupla wipe ons at the end of a job and the dust factor goes way down.

6. 
   toolman50 | Apr 28, 2007 02:52am | #15

   Thanks blewcrowe and BigK for the additional information.

   Toolman

2. 
   HowardAcheson | Apr 26, 2007 03:11am | #5

   How long did you allow the finish to dry between coats and how long to dry after the final coat?

   Oil based finishes harden in two steps. The first is the evaporation of the solvents. When this happens the surface is dry to the touch but the finish has just begun to cure to final hardness. Full curing takes 3-4 weeks

   Urethane resin is added to vanish to increase the finish's resistance to abrasion or scratching. Sanding is scratching and poly does not scratch evenly like varnish. It is not a good finish to "rub out". For the best success, you should let the finish dry and cure for 3-4 weeks until it is really fully hardened.

   Poly will never regain the gloss that it has right off the brush or out of the gun. At best, you can work it to a satin gloss.

   Howie.........
1. 
   toolman50 | Apr 26, 2007 03:59pm | #6

   Howie,

   I only let it set 48 hours between coats and about that long on the finish coat before trying to rub it down.  How long should you wait?  Does each coat of the poly need to be completely cured before working it, or just the final coat.  Thanks for explaining this to me.  I obviously have alot to learn about how different finishes act.

   Toolman

1. 
   HowardAcheson | Apr 26, 2007 05:18pm | #10

   For between coat sanding, allowing 24-48 hours is generally enough. However, this is based on the film thickness. Thinner dries faster. It's the 3-4 week curing time that is necessary if you want to try to rub out the surface. Keep smelling it. If you detect any finish odor, the material is still curing. Wait until the odor ceases.But, as I said before, poly does not rub out well to a high gloss. If you want a varnish that does rub out well, use a non-poly interior varnish. Exterior varnishes are "long oil" varnish meaning more oil is used to make the finish somewhat softer and more flexible so that it maintains its adhesion in exterior applications. There is almost never a situation where an exterior varnish (or poly varnish) should be used in an interior application.Let me suggest you purchase Flexner's Understanding Finishing. You can get it at Amazon. It will describe all the various finishes, when to use what and then how to apply it. Oil based finishes are problematic for spray applications. Because they are slow drying, the overspray remains liquid and creates a crust on everything in the area. The spray itself also disturbs the air and suspends dust that later settles on your finished surface. A spray booth is the best thing it you want to spray oil based finishes.Howie.........