Glue Spots that Appear After Stain is Applied
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A description of scraping, sanding, and touch-up techniques for correcting unsightly glue spots, with some advice on prior prevention strategies. June 8, 2011
Question
I am a cabinetmaker and my business is so slow that I am finishing my cabinets (I do not normally do so). How do you handle the problem of finding glue spots while staining? I have tried sanding the area and then restaining and found that the paper clogs badly and the restained area does not match well. I am using a gel stain.
Forum Responses
(Finishing Forum)
From contributor M:
Welcome to the club. Even on the factory made doors I order, glue spots appear out of nowhere when staining. And, of course, they are nearly impossible to see before staining.
I scrape off the glue with a very sharp scraper and use no sandpaper. This doesn't seem to seal the grain like clogged sandpaper does, causing a light spot in the reapplied stain. But you have to be almost surgical in scraping not to leave scratches.
Someone once told me to spray bare wood with lacquer thinner to darken it temporarily so you could tell where the glue is before staining. Then you can sand it without changing the stain absorption. But, being kind of lazy, I have never tried it.
From the original questioner:
Thanks. Do you use a flat blade type scraper?
From contributor M:
I use a narrow flat-blade scraper on which I have ground the edge to a slightly convex line. This helps the corners of the blade to not make scratches.
From contributor D:
It probably gives you a better appreciation for what the finishers have been dealing with. Now that you see the issue, the best way to deal with it is to spot sand the area back to raw wood and then blend the stain back in. If you use 150 sandpaper followed by a sanding sponge in 180, it generally goes pretty well if you can get on it right away after you stain.
Wiping down with mineral spirits will also many times make the glue stand out so you can fix it before staining. Hope everything works out for you.
From contributor I:
I usually leave the glue spot alone until after I have applied my sealer coat. Then I touch up the color using Blendal powders mixed with dewaxed shellac applied with an artists brush, and proceed with my finishing schedule. You can wipe down the surface prior to staining to help identify any missed glue spots, but I usually use naphtha or naphtha with a little mineral spirits. Another technique from Bob Flexner's "Understanding Wood Finishing" is to add a UV colorant to the glue. The glue would then glow when exposed to UV light (a black light).
From contributor H:
Sand with 120 by machine then hand, wet the surface down with water. While the wood is wet, check for glue spots and circle with a pencil. Once dry, hit the spots with a cabinet scraper, then sand with 150 by machine, then by hand with 150.
From contributor L:
I dip my sandpaper in the stain and sand the spot by hand, wiping occasionally to see how it is progressing.
From contributor A:
Try to minimize excess glue in the first place and catch it as soon as it happens so that you can remove it from the wood. Wipe your wood down with denatured alcohol and massage glue spots with a pad before you stain. Avoid fine grit sandpaper to remove spots. Try some spray toners to blend away the spots if needed.
From contributor G:
The response about Blendal color was good. Look to Mohawk - they have Blendal sticks. Rub the stick with your finger and apply like a woman would her makeup. Spray your next coat to seal and the color is locked in. You can dab multiple sticks to get the right color. If it isn't right, take a rag and rub before spraying.
From contributor E:
I have also heard that you can add or have added to your glue a dye that will show up with black light. You can mount a black light to the end of the sander or have a hand held one to wave over the parts in question.
From contributor S:
All glues will fluoresce under UV light - you don't need to add anything to them.
From the original questioner:
After reading these replies I took an unstained piece which I had to glue up and wiped some lacquer thinner on it and sure enough, the areas that still had glue showed very clearly.
What does the term "ghosting" mean?
From contributor H:
A ghost is either a glue spot or a fill spot that you think you sanded out and, upon staining or finishing, shows up like a halo around the area. Anytime the porosity of the wood is altered you will get a different penetration of your stain or finish. They can be touched up after sealing, but then you will get a color shift since you are above the wood. Best to remove them before staining.
From contributor B:
I run across this all time as most of my clients don't build their own doors and drawer fronts. All of my base colors are sprayed and they are dye based. From 100% dye up to 50/50 with a pigmented stain (I use all WB dye/stains). The gel stain probably makes it harder to get the glue stains out as you try various methods. As soon as I see the glue spots, I sand out the spot with 220 and re-wet the area and wipe it real good. This method has worked in all but a few instances when the glue was deep in a corner or underneath molding. Then I'll SS it, go in and scratch/sand whatever it takes and re-color with a stiff artists brush.
From the original questioner:
I wipe all glue off with water as soon as I can, then sand to 120-150 depending on wood species. Did not think this problem was happening that much. From now on I will check all of my glue-ups before they go out the door with thinner or light. Any recommendations for the light?
From contributor C:
Titebond makes a yellow PVA glue that will fluoresce under a black light. In my area Louis and Company will run a special that gives you a small handheld black light for free if you purchase two gallons of the glue. Don't remember exactly, but it was a little over $20 a gallon. There is something to say about using methods to help minimize this from the get go.
