Shop TalkRick Mack's Guide to Bleaching Wood
Bleaching wood is accomplished by using one or both of two chemical processes designed specifically for wood.
The first chemical method is the use of 'OXALIC ACID' which is best used to lighten wood only slightly. Oxalic acid is available from some hardware stores, wood specialty shops and from catalogs. It comes in crystals which are mixed with warm water and applied with a brush or sponge. Minor wood discolorations are a good candidate for this chemical but it is not really effective at removing major dark areas on hardwoods. This is the active ingredient in most 'deck washes'.
The second and most effective wood bleach is a two-part chemical system consisting of an 'A' bottle and a 'B' bottle. Bleaching is accomplished by either mixing equal parts of 'A' and 'B' together and applying the solution to the wood or by applying the 'A' solution first, letting dry it completely or at least set a few minutes and reach a 'damp' condition, then applying the 'B' solution to the wood using each solution at full strength. The working effect is the same but each brand has slightly differing instructions. I now prefer to use 'DALYS' brand which can be applied EITHER in a mixed 'A' and 'B' solution or the 'A' solution first then the 'B' solution. Very convenient. In the past I used 'NU-TONE' brand quite successfully but I have not found it to be available in the northwest. I would avoid the 'JASCO' brand A&B bleach as it leaves a crusty residue that is most difficult to remove. Please read the instructions carefully on whichever brand you choose!
CAUTION: These solutions are HOT AND CAUSTIC, ESPECIALLY THE 'B' SOLUTION, THEY WILL MAKE TOAST OF WHATEVER THEY TOUCH-EXCEPT WOOD! Always use rubber gloves, don't spill the stuff on your paint, on your clothes or on your skin! It will not kill you but when you see your finger tips turning white, you will soon have hot fingers! Rinse thoroughly with water for a couple of minutes and you 'll be fine. It is a good idea to buy a bunch of those really cheap brushes for this task as each one used in wood bleach will melt fairly soon!
Virtually all of these A&B solution bleaches require a 'neutralizer' such as plain water, water mixed with white vinegar or some secret concoction that they sell you along with the bleach. Water always works as a neutralizer in a pinch! The same neutralizer step is also necessary when using the OXALIC ACID type wood bleach. Again, consult the specific instructions that come along with the bleach that you have purchased.
How do I know if MY wood needs to be bleached?
If YOUR wood has ever been exposed to the elements without varnish for more than a few weeks, it should be bleached during the refinishing process.
Since most of our cars and probably your car too, have been kicked around for many decades, there is not much chance that the varnish has remained intact on any of them for all of those years. Bleaching is going to be necessary for almost everyone who is restoring a woodie today and if carried out properly will certainly improve the quality of the finished project. Without bleaching, many areas of the wood after varnishing will be far darker and unevenly toned than they were when the car rolled off of the showroom floor. This effect may be hard to understand when looking at decent wood that has been carefully stripped of its old varnish and sanded but this wood will likely appear differently after the application of new varnish.
When restoring my first woodie, a 1940 Ford with very decent wood, I learned about bleaching only AFTER all of those sixteen beautiful coats of varnish had been successfully applied. How come this wood is still so dark after all of that sanding? Hmmm, I wonder what that stuff on the hardware store shelf labeled WOOD BLEACH is?
Definitely a learning experience. It took TWO more total refinishings to get it right!
Here is how to do it right the first time ---
Sand your wood; sand your wood some more. Disassemble into as many individual pieces as you can to get the wood parts clean and sanded. You need to sand your wood until you have removed ALL of the beat-up, gray, weathered surface layer and you are looking at solid, clean wood. Yes, your car gets slightly smaller every time it is refinished and you cannot make weather-checking cracks go away! I start my sanding with 80 grit using a DeWalt random orbital sander to do the dirty work. A 'disc' sander can be very useful here to get at the inside contours and to remove a deeply weathered surface. Be careful using that disc, it can zip off a lot of your good wood fast! In the right hands, the disc sander is a terrific tool. Continue to machine sand through the grits down to 150 grit BEFORE bleaching. Clean up the tight spots by hand sanding. Remember: After the bleaching process, you will only be able to sand lightly with 220 grit by hand to remove the remnants of grain fuzz lifted by the bleach and its neutralizer. Adequate in-depth sanding preparation of the wood is critical for the bleach to do its work properly.
If you are using A&B bleach, pour 10 or 12 ounces of 'A' into a plastic cup. Using the cheap brush, begin applying the bleach to the wood. It is best to start with a piece or two of trim that you can control while you get used to the feel of applying the solution. Work quickly and evenly-no drips on the rest of the wood as it will bleach the drip spots and they may not even out in tone later! Any missed spots will be darker, perhaps forever. Be thorough! Wet all sides and surfaces, back and front; get everything with the bleach. After the wood is completely wet with bleach, take a rag and wipe off the excess leaving no pools or puddles in the corners, etc. Let it dry to at least damp, with some brands 'dry'. As the 'A' solution dries, the wood will actually grow darker! Now pour 10 or 12 ounces of 'B' into a different cup. Using a separate cheap brush, do the whole works all over again being very careful to cover every bit of wood that was originally coated with the 'A' solution. Remember to use the rubber gloves! The 'B' solution is the HOT one! When the 'B' solution has been completely applied, wipe off the excess again with a clean rag or heavy paper towel. Set the wood out in the sun to bleach and dry. Bleach works much more thoroughly in the sun! Cool huh?
When the bleached wood has dried completely it should be several shades lighter. Now is the time to apply the appropriate neutralizer. Read the instructions of your brand of bleach and follow them. After the neutralizer is dry, check out the wood. Does it look satisfactory? Is it light enough? Sometimes a second application of the bleach is necessary. If you think the wood needs it, do it.
Perform the above procedure to all of the wood you wish to bleach. It is best to bleach ALL of your wood so it will ALL be the same tone when your work is finished. You might even consider bleaching the INSIDE wood as well. Bleaching really brightens up the appearance of the finished wood. I sometimes find it necessary to also bleach NEW wood replacement pieces so the overall tone is uniform between old and new wood. Before applying the varnish, I do attend to replacing the warm wood patina/tone that the wood bleach removes during the bleaching process. See my Finishing Wood instructions for more details on this important process.
Some of the potential problems you may encounter include uneven bleaching, missed areas and loss of the original, warm wood patina. A few slightly off-color streaks almost always appear somewhere. I have never been able to figure out why this occurs but a great way to get a final even tone is to utilize the 'OXALIC ACID' type bleach for a final coat in this process.
Get some of this bleach, good to have on hand for minor discolorations, mix it and apply to all wood that has been bleached with the A&B type bleach. Set the wood out in the sun again, let dry and neutralize. When finally dry, the wood should quite light in tone and with a feather light hand sanding with 220 grit it will be ready for a new finish!
The warm wood patina can be reintroduced by mixing up a light home made stain of artists oil paint 'raw sienna' and 'burnt sienna' along with some thinner and PURE BOILED linseed oil. Again, this process is covered fully in my Finishing Wood.
Rick Mack Enterprises
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