Thoughts on Bleaching Walnut
Tips and cautions for a big job involving two-part bleach. October 20, 2013
Question
I have a job bleaching walnut. I did up a sample using a 2 part wood bleach and it was approved. However, the job got much bigger - it now has many square feet of paneling. Are there any tricks to evenly bleaching large panel jobs? And would oxalic acid be any easier to use if appropriate?
Forum Responses
(Finishing Forum)
From contributor R:
Oxalic acid, although a bleach won't do as good a job in removing the color as the two part will. I would continue with your job using the same method you did on your sample.
I have had good results using two application processes. You can use either a pesticide sprayer or a pressure pot and a spray gun. HVLPs work well. We have done many banks and brokerage houses this way. On jobs where the wall panels were impossible to remove, we applied the bleach starting from the bottom and sprayed upwards. This allows the bleach to run into an area that's already wet.
WoodKote company has a two part bleach. I think it's the old SpeedyWay formula and it's worked well for our applications. Walnut can/could turn a greenish color if you drench the area you're bleaching, so be careful. Misting on an even coat is the way to apply it.
Even if you're not bleaching wall panels that are in an upright position, I would still look into spraying it, as you can do a large area in a short amount of time. This bleach does not leave a crusty residue on the surface like the old Jasco used to, and even though it says it doesn't need a neutralizer, we still wipe down the dry wood with a mixture of vinegar and warm water. Let it dry up real good prior to starting your finishing schedule.
From contributor M:
I totally agree with the spray-on technique. After the acid neutralization, I'd wash with methanol, not DNA, wood alcohol. Walnut will often greenify; just a light spray with dilute red aniline dye will make it look a little more normal. Don't do it automatically, just if green is bothersome to yours or the customer's aesthetic.
From contributor O:
2 part bleach is some pretty nasty stuff. It will burn you (once you feel it burning, it is too late), so be very careful about breathing in the vapors. Even after neutralizing, the sanding dust will cause burns if they come into contact with moist surfaces, like lungs. Also be aware that bleach is an oxidizer and will rust any steel that it comes in contact with.
The number one rule when working with bleach is: wash your hands before going to the bathroom. Don't ask me how I know this.
Here's an article that might be of interest:
Bleaching Wood
From contributor A:
If you read the instructions on any 2 part bleach, the first thing you'll see is to mix in glass or plastic containers. Heat and pressure are generated when the mixture comes in contact with metal. Put it in a cup gun or pressure pot, and that mixture will be smoking in 10 minutes. Those vapors can't be good for you, either. Please be careful - these are potent chemicals, even hotter when mixed. One splash in the face and you'll be really sorry.
From contributor R:
Many companies make plastic liners either for a cup gun and even a pressure pot. HVLP cups are made from plastic. I believe in safety but let's not spread panic rumors. Bleach has been applied via a spray gun for eons and eons. Like any other step involved in finishing, caution should be of the utmost importance. Common sense is also advised.
From contributor A:
Common sense would dictate that you read the instructions.
From contributor R:
I can't argue your point, but at the same time a little ingenuity could come into play too. A plastic pot liner in a pressure pot or a 3M liner in a cup gun would be a safe way to apply the bleach. The pesticide sprayers from ACE or Home Depot are made out of plastic. If someone was hesitant to use a HVLP or pressure pot or a siphon cup gun, those would be a safe option instead.
From contributor T:
I have had an increasingly hard time finding two part wood bleach. Any reliable sources?
