Replies

1. 
   SteveSchoene | Nov 05, 2007 03:38pm | #1

   There is something missing here.  Sanding with 320 grit is most commonly recommended between coats, and works well for most people.  This leads me to think that you are seeing something else.  The most likely thing is that there are sanding scratches in the wood itself that weren't removed before applying the first coat.  Unless you use strong light at a low angle it's possible to miss these even past the first coat if that first coat mostly sinks into the wood.  When you start seeing some sheen from the second and subsequent coats the scratches might become apparent even in overhead light. 

   You don't mention what kind of varnish (brand name) you are using.  It might help to know the brand and how you are thinning it. 

2. 
   saschafer | Nov 05, 2007 04:52pm | #2

   I have to agree with the other Steve. It would take extra effort to apply polyurethane so thinly that it didn't fill in scratches from 320 paper.

   The scratches you're seeing must be coming from somewhere else. Can you describe the complete sequence of preparation that you used?

   -Steve

    

1. 
   notenoughtime | Nov 05, 2007 07:37pm | #3

   Please forgive any unnecessary information.

   I am clear coating a table top that I built from old fir using Minwax fact dry gloss for the base coat and finishing it off with the semi gloss.  The table was dyed (water) and then stained using minwax only after the table was thoroughly dry.  The table actually needed 4 coats of full strength gloss before it was sealed (ie. before all dry spots disappeared).  I have finished perhaps 6 table tops before and have never seen anything like this.  I used my Random orbital sander with 220 between each coat until the table was sealed.  I then switched to 320 and sanded by hand, applied another coat of gloss for good measure and then the semi.  Unfortunately the semi came out looking cloudy (this was the next issue I was going to bring up).  As a result I took out the R.O. sander again and decided to try again.  I then applied gloss, lightly sanded with 320 followed by semi.  I got scratches and cloudiness once again.  I do not believe I could have sanded down to the wood for a couple of reasons:  A) very light pressure B) the many established coats beneath.

   FWIW I have been using a floor application pad to apply the poly.

   Any ideas regarding the semigloss cloudy issue would be greatly appreciated as well.  I'm wondering about just using gloss and then toning down the shine manually in some manner.

   Thanks N.E.T.

    

    

1. 
   saschafer | Nov 05, 2007 08:04pm | #4

   Were the other tables also made of Douglas-fir, or something else? Softwoods can show scratches much more readily than hardwoods, especially cross-grain scratches that result from random-orbital sanding.

   My initial guess is that the finish isn't fully cured. That could explain both the appearance of scratches (you're just digging into a not-quite-hard finish) and possibly also the cloudiness. If the situation doesn't improve in a couple of weeks, it's conceivable that there was something in the wood that is preventing complete polymerization (or it could just be that the varnish is too old). If that's the case, there's not much you can do except strip it off, seal the wood with a coat of shellac, and try again.

   In general, my approach would be to first random-orbital sand to 220, then hand sand along the grain with 220, then apply the finish. Between finish coats I would hand sand along the grain with a very fine Scotchbrite pad, or with 320 if necessary to remove any finish defects. I wouldn't use the random-orbital sander between coats.

   -Steve

    

    

2. 
   user-83153 | Nov 06, 2007 01:06am | #5

   I second what Steve said about not using a power sander between coats. That's overkill, all you are trying to do between coats is knock down any imperfections and get a light scratch pattern for mechanical adhesion.

   The cloudiness issue with the semigloss is almost certainly the result of not mixing it enough. The flatting agents need to be thoroughly mixed every time you use it and occasionally while applying. If you used this can of varnish before and didn't mix it enough the next time you use it there will be to high a concentration of flatting agents. If it isn't mixed completely it will have some areas that are glossy and some that are dull or cloudy.

1. 
   notenoughtime | Nov 06, 2007 06:00am | #6

   Thanks for the advise all.

    

   N.E.T.

    

1. 
   JMadson | Nov 06, 2007 03:25pm | #7

   I've had good luck applying poly with wet-dry sandpaper. Use 600 grit and thin the poly in half. Use the poly as the lubricant for the sanding. Wipe off all of the excess when you're done. 

2. 
   saschafer | Nov 07, 2007 05:09am | #9

   Something occurred to me today while I was sanding some shellac: Some finishing materials have an annoying tendency to build up into hard little "beads" on the sandpaper (shellac is especially prone to this). I haven't tried random orbital sanding of the Minwax poly, but it's possible that that's what happened to you. Once those beads form, scratches are all but inevitable.

   -Steve

    

3. 
   highfigh | Nov 07, 2007 05:15am | #10

   Instead of using sandpaper with the poly, I have used Scotch Brite pads with good success. The pad will pick up most, if not all, of the beads.
   "I cut this piece four times and it's still too short."

3. 
   Julmer | Nov 06, 2007 07:54pm | #8

   Agree with the mixing comment and semi-gloss.

   I experienced the same cloudiness problem with semi-gloss on a large table top and only figured it out after redoing the entire top of a large table.

   JohnU