Carpentry and Woodworking - Urethane problems
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EW Begley
05-14-02, 02:10 PM
I am applying polyurethane to a tabletop but I cannot seem to get it smooth. Each time there are tiny bubbles (I tried smoothing them after application with the brush at 45 degree angle) and uneven patches that were not visible when it was wet. This is a satin finish. I have sanded (220 grit) and reapplied about 4 times now after vacuuming and wiping away the dust, and I think I will spend the rest of my life on this project. I did not shake the can but carefully stirred it, and have tried an expensive China bristle brush as well as a cheap brush and a foam brush, all with the same result. Do I need to start over?
George
05-14-02, 05:57 PM
E.W.
There are several techniques you may try to get rid of the problems.
1- The final pass over and area (to knock down the bubbles) should be made with the brush almost vertical and the bristle tips just barely touching teh surface.
2- Thinning the urethane (15-25%) will also help.
3- Place a couple of lamps near and about 18" above the surface of the table. When examining the table to see what you've missed, look across the table toward the light with your eyes just slightly above the table surface. Any mised spots will show up immediately as a dull area - what you just covered will be shiny.
Check each area as you go so you don't have to some back and rebrush an area that's started to set.
The greatest all-time sin with most brush applied finishes is over brushing. Lay it on, smooth it out, 'tip' it off and lEAVE IT ALONE.
There are several techniques you may try to get rid of the problems.
1- The final pass over and area (to knock down the bubbles) should be made with the brush almost vertical and the bristle tips just barely touching teh surface.
2- Thinning the urethane (15-25%) will also help.
3- Place a couple of lamps near and about 18" above the surface of the table. When examining the table to see what you've missed, look across the table toward the light with your eyes just slightly above the table surface. Any mised spots will show up immediately as a dull area - what you just covered will be shiny.
Check each area as you go so you don't have to some back and rebrush an area that's started to set.
The greatest all-time sin with most brush applied finishes is over brushing. Lay it on, smooth it out, 'tip' it off and lEAVE IT ALONE.
Davef15
05-15-02, 10:25 AM
The application of poly, by brush, without air bubbles, is an imperfect art - One I have not mastered after 20 years of doing it. I've tried all different brushes and techniques. Here is what I do for large table tops. Sounds stupid and contrary, but it works for me.
I put a couple of coats on with a good brush, sanding between coats with 220 grit paper. Be careful at the edges that you don't sand through the finish. After the second coat, I sand rather aggressively again with 220 - usually with a vibrating sander. Move VERY quickly and again watch the edges. ThenI brush on the third coat and immediately, with a clean cloth like an old Tee shirt, rub it off. It can get a bit messy and you have to work fast. You want to rub it dry. It will look like heck after you are done but come back the next day and you will have a beautiful smooth surface.
I put a couple of coats on with a good brush, sanding between coats with 220 grit paper. Be careful at the edges that you don't sand through the finish. After the second coat, I sand rather aggressively again with 220 - usually with a vibrating sander. Move VERY quickly and again watch the edges. ThenI brush on the third coat and immediately, with a clean cloth like an old Tee shirt, rub it off. It can get a bit messy and you have to work fast. You want to rub it dry. It will look like heck after you are done but come back the next day and you will have a beautiful smooth surface.
CliffLm
05-15-02, 01:54 PM
Lately I've been using Wipe on Poly by Minwax, and getting some very nice results. It's not so tricky to get a nice smooth finish.
fewalt
05-15-02, 03:45 PM
EW Begley,
One of Geoge's recommendations is the best. Simply thin the poly(oil base) with mineral spirits. Sometimes I thin to a 50/50 mix.
It turns out sorta like a wipe-on poly - (a hint that you can make your own)! It's so thin that bubbles almost cannot form because it levels so fast. Between the coats I sand with 320 or finer grit paper.
fred
One of Geoge's recommendations is the best. Simply thin the poly(oil base) with mineral spirits. Sometimes I thin to a 50/50 mix.
It turns out sorta like a wipe-on poly - (a hint that you can make your own)! It's so thin that bubbles almost cannot form because it levels so fast. Between the coats I sand with 320 or finer grit paper.
fred