Problems Caused by Water and Oxalic Acid Wash after Stripping Furniture

Rinsing with water and oxalic acid after stripping a piece with methylene chloride is standard practice. But it has to be done with care. July 15, 2014

I do quite a bit of furniture stripping in the shop that I work for. Iím having a lot of problems with veneer peeling and curling due to the fact that the shop uses water and oxalic acid to wash stripped pieces. I came from a shop that strictly used a solvent wash process and we never had this problem. I was laid off and had to find a new job. Upon moving to this new shop I had never heard of using water to wash furniture. I suppose my question is how do we avoid the warping and twisting of not only veneer but other hardwoods as well when using a water wash? Itís not that I prefer to wash with solvent, Iím just looking for a way to avoid creating extra work for myself, like gluing veneer back down. We also use a water gun that uses compressed air and this seems like a very bad idea. Any thoughts would be greatly appreciated!

Forum Responses
(Finishing Forum)
From contributor S:
About all you can do is squeegee off the excess water and blow out the nooks and crannies. The water/oxalic acid has been used for a long time to clean off the stripper and brighten the wood after stripping. It sounds like just too much of it and it was left on too long. Are you tank dipping or using flow-over? If left in the tank too long that could be part of it and the chemicals are penetrating and softening the glue and then the power washing gets more water there and lifts the veneer. Is the veneer intact after the stripping and only comes loose after the wash? Try to determine exactly where it occurs and then address that issue.

I am curious what your new employer thinks, is this just acceptable? Some strippers just want to get the stuff off with as little hand work as possible and don't get concerned about the collateral damage. If the shop also does refinishing I would think they would not want to deal with all the repairs required or do they just strip and let the client deal with the damages. If you guys are repairing all this loose veneer it must be hard to make any money off those jobs. I would turn down the power washer pressure, use a soft brush to help remove the debris and use minimum water and get it wiped off.

From Contributor J:
I agree with Contributor S. We've used water after wash for many years without many problems except on pieces that were heavily compromised. It was with mild pressure, then squeegeed and/or towel wiped and placed to dry with good air circulation. Extremely delicate pieces went into the spray room (ventilation) for a solvent wash. Newer particle core pieces were more of a pain than anything up through the 40's.

From contributor A:
I would never rock the boat with a new boss. I would never sand oxalic acid every day either. There's really no need to use it. As for the pressure wash, don't saturate the piece, just use it for a few blasts as needed (carvings, intricate moldings, etc.). I would also keep air moving on my work the whole time to help the water evaporate faster. If youíre going to lunch leave a fan blowing on your work. On the veneer you should use a lighter touch. Any stripper will attack the glue line eventually, especially on veneer. I've done a lot of refinishing myself and every job would have unique challenges. You learn what not to do by making mistakes and having to fix them. Good luck with the new job, and don't choke on oxalic acid dust.

From the original questioner
We use a flow over system with a nylon bristle brush. About two months before I was hired the shop was sold to a new owner. A great guy but he had no experience in this trade at all. The two guys that worked there as the business was sold stayed on. I believe they are taking advantage of his naivete and keeping many major issues from him. I have spent as much as three-four extra hours gluing veneer back down for restoration jobs that the other two stripped. I was shocked! I knew something was wrong within the first week. The common practice at this shop was to strip with the flow-over, transfer to the wash tank where it gets an oxalic acid wash, then blasted with a pressure washer. The pressure washer is basically a water cannon, itís scary. Then set in another tank to dry, without wiping or using a squeegee. I have brought this up to my employer and he urged me to find some answers, so itís definitely not okay with him.

From Contributor J:
I never treated oxalic acid as a routine after-wash - just water or a stain puller like sodium sesquicarbonate that was sprayed on with a garden sprayer, scrubbed with Scotch-Brites and then washed off with water. Then we use oxalic acid to clear up sun-grey/rust/mineral/water stains. We always rinse it off with clear water and let dry before sanding. Is the stripper so caustic that it alkali burns the wood so they have to use oxalic routinely?

From the original questioner
I have never seen any evidence of wood burning. I have also found it very odd that they use it every time. Most furniture comes very clean after we have stripped it with the methylene chloride. Itís a very odd situation Iím in here. I work with two men twice my age who seem to know very little about the why's of their method. Iím young and they don't recognize my opinions for having any weight. When I ask questions I have literally been told that they don't know!

From contributor F:
Water wash, yes. Power wash rinse is a valid, safe means of rinsing but not in all cases and it depends heavily on good technique. You've received good advice on that front and there is much more tech data out there if you look for it. I see another side to this and if I'm reading it all wrong I apologize in advance. Decide if you want to work at this shop or not. If yes or maybe, then for the next three months dedicate yourself to listening and executing their procedures to the letter.

Ask honest questions when you need to but keep it simple. I'm sure they are not interested right now in a debate with the new kid about the pros and cons of various stripping method. You may have all the answers but now is not the time. If you can't stomach the way they are telling you to do things then you need to go. If you show respect to their ways even if you don't agree chances are you'll get your shot at making changes happen down the line. All bosses like any ideas that get the work done better and faster at less material cost.