Glue spots under stain

Question

I have two pieces of plywood that I joined with biscuits and wood glue (wiping away all excess glue after joining the two pieces. I then sanded the whole piece down to 220 grit. After staining there is a large light streak where (I'm assuming) glue was left.

Can this be fixed, and if so how?

Answer 1

The problem appears to be that glue has sealed the pores of the wood, preventing stain from penetrating. In order to fix the stain, you'll first need to get to wood that's not sealed. I can think of two options:

1. Remove the glue from the wood. You might be able to use a solvent appropriate to the kind of glue you used to loosen and weaken the glue, and then scrub with something like a Scotch-Brite pad. How well this will work will depend on whether the glue is really absorbed into the wood or just layered on top. I've heard that vinegar can work as a mild solvent for PVA (wood) glue, so you could try that.

2. Remove the wood that has been sealed to get down to bare wood. In other words, sand or scrape more of the wood away. With plywood projects, though, it's very easy to sand right through the top layer of veneer.

Until you get down to bare wood, the stain won't be able to penetrate evenly and you'll continue to have problems.

Here are some strategies for avoiding this problem in the future:

1. Use less glue. If there's less glue, there's less to squeeze out and cause problems, but it's hard to get enough glue on the joint without having some squeeze out.

2. Protect the wood. People sometimes use clear packing tape to cover the wood near joints during glue up. This (mostly) prevents the glue from contacting the wood. Glue and tape can then be removed after the glue has set enough that it's no longer liquid. Sometimes the glue still seeps under the tape, though, so this isn't entirely effective.

3. Avoid wiping. If you don't use too much glue, you can usually just let it squeeze out and form little beads along the joint. When the glue dries (or nearly dries), it's easy to remove by running a sharp chisel along the joint.

4. Wipe effectively. If you want to wipe the glue away, use sponge or towel that's quite damp. PVA glues can be cleaned up with water before they dry, so you can wipe excess glue away with water. You need to be really thorough if you go this route since any glue you miss will likely be pushed into the wood, resulting in the same problem you have now.

One of the big hassles with glue stains, as you've discovered, is that they can be hard to detect until you stain or finish your project, and they're a pain to fix at that point. If you have this problem a lot, you might be interested in Titebond II Fluorescent glue, which glows under black light so that you can clean up before the glue dries.

Answer 2

At this point, you'll need to sand or plane and refinish.

For future reference, don't wipe the glue off with either a wet or dry towel, because you'll mostly succeed in smearing a thin layer of glue across the surface. Instead, either let the glue dry completely and scrape it off with a chisel or paint scraper, or let it dry until it's tacky and shave it off with a razor blade or putty knife.

Answer 3

Because you've used ply this may be unfixable at this point.

If your ply is decent enough quality that the surface veneer is thick enough to permit you sanding (or scraping) back to bare wood, without sanding through to the next layer, then yes you can fix this. This would simultaneously remove the glue-saturated surface fibres along the joint so that you could get a good stain result when you go to refinish. Unfortunately it's doubtful the plywood does have a thick enough face ply.

Side note: it's hard to tell for sure from the picture but this plywood may benefit from using pre-stain conditioner before staining (see previous Question).

For future projects, while wiping up glue squeeze-out is perhaps not the ideal method (wide range of opinions on what is the best method, see Note bottom) it can be done with greater care and attention to ensure good results. Some tips:

• Always use warm water if possible.
• Cloth should often not be "barely damp" or "just damp" as per the instructions in so many guides, a little wetter than damp works better almost always. But you must clean up excess water as you go to prevent problems.
• This method will nearly always cause raised grain. Expect it and plan ahead to deal with it after the glue has cured.
• Always use a clean cloth and fold it periodically during wiping operations to expose fresh fabric with no glue already soaked into it.
• Be methodical and thorough, do not expect that one wipe down the length of the joint will be enough.
• For squeeze-out on inside corners an old toothbrush is a boon, it can help greatly in getting the last traces of glue from right at the joint line that the folded corner of a cloth often misses.

Last but not least:

• Expect the cleanup to take as long or longer than the joint took to glue and assemble. Having this kind of timeframe in your head at the outset will help ensure the job isn't rushed.

Note
While wiping does sometimes lead to this sort of problem the methods that rely on letting the glue dry partially (to a sort of rubbery consistency, when it cab be picked off with the fingers) or fully (when it can be scraped, chiselled or even sanded off) are not perfect either. In both of these cases wood glue can penetrate into the surface wood fibres and removing the visible glue does not always get all of it, leading to exactly the same problem as you've experienced, albeit on a more limited scale.

Another issue with scraping off glue that has fully dried is that it is bound strongly with the surface wood fibres, and on splinter-prone woods this will inevitably lead to tearout. It's not the ideal method for use on plywood either because of the thin surface veneers common to modern material (even where it is of good quality), which can be physically ripped free as you scrape.