Furniture Finishing & Restoration
Spray Finishing Problems
"Runs & Sags"
Runs and sags in the finish are caused by applying the finish too heavily. Though usually associated with spraying, they can also happen when applying the finish with a brush. To avoid them, simply use thinner coats. Generally, the thinner the finish is, the thinner you will have to apply each coat to avoid the problem. If they do happen, they're pretty easy to repair.
Fixing the Problem
The approach I use to eliminate runs and sags is to cut or scrape them down and then sand them level to blend in. If the finish is soft, the thick portion of the run will slice off easily. If it's hard, then it has to be scraped. You can use a card scraper, or my favorite, a new single edge razor blade. I bend the blade slightly to limit how much of it contacts the surface and to avoid making scratches with the sharp corners.
Slicing the Run - Soft Finish
If you catch the run after the finish dries and before it hardens, you can slice it off with the razor blade. If it's too soft and is sticky, give it a little more time. Holding the blade at a low angle, carefully slice the thickest portion of the run or sag from the finish. Sometimes it takes more than one pass, and a steady hand and vigilennce is needed to avoid cutting too deep, but I found it an easy technique to master. Once the bulk of the surplus finish is removed, sanding the area lightly levels it nicely so that the run or sag is no longer noticeable.
Here's another example with a soft finish. In the picture on the left, I've started to slice the run and you can see the thick portion that's being removed (close-up in the center picture). The picture on the right show the run sliced off completely. It's ready for a light sanding to level it out. I usually use a sanding sponge for almost all the in between coat sanding I do, but you can use a felt or cork sanding block if you want to. Just be careful not to sand too much and cut through the finish. Lift the sponge or block frequently to check your progress.
Scraping the Run/Sag - Hard Finish
The bow in the blade really helps to control how much of it contacts the surface. And that gives you precise control over both the slicing and scraping technique. You always want to position the blade so the the sharp corners don't come into contact with the surface. Otherwise, the blade will create scratches and possible damage the finish making more work for you. In the two pictures, I'm scraping a sag from the surface. Notice the blade is at a pretty high angle to the surface when scraping and the corners of the blade are not touching. As you pull the blade along the length of the run or sag, you can feel it working, as well as see exactly where the finish is being removed.
Whenever you're getting ready to fix a run or sag, try scraping first to see how hard the finish is. If it scrapes well, it probably will not slice off. Trying to slice a hard finish is a lot more difficult than scraping and you'll probably end up with some gouges. It may take a few passes along the length of the run or sag to flatten it out; just take your time and keep a close eye on your progress. Once it's scraped, a very light sanding with 220 or 320 grit should be all you need to blend it in with the rest of the surface.
© Copyright 2001-2005. Paul Snyder. All rights reserved.