From DIYinfo.org
| Oxalic Acid |
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| Why use oxalic acid? |
| Oxalic Acid is used as a Stain Remover and Brick Cleaner. |
| What is it? |
| Oxalic acid is a naturally occurring biodegradable organic product which can clean metals, remove cement residues, act as a mild bleaching agent and which is very efficient at removing rust and blood stains. |
| See also |
| Oxalic Acid,How To Restore Timber Colour |
| How To Remove Stain - Grime After Paint Stripping |
| Using Paint Stripper,How To Hand Strip Items |
| Water And Heat Marks |
| Visit |
| Diggers Home Page |
| Diggers Oxalic Acid Catalogue |
| Diggers Catalogue |
Bleaching removes the natural colour from most timbers, and can eliminate undesirable colour variations in natural timber. It can also aid in the removal of unwanted ink and stain blemishes left in timber after paint stripping.
Many of the popular timber stain colours require a very light background to be effective. To achieve this effect on coloured timbers such as walnut, maple and oak, it is necessary to remove or lighten the natural colour (i.e. when using liming white colours).
1. Test a piece of the surface for acceptance of the bleaching process.
2. Don’t over bleach; this tends to destroy the minor contrasts in the grain, and lessens the quality of the final finish.
3. When strong bleach is used, wash thoroughly by spraying with clean water and sponging down (the garden hose is good for this).
4. DRY thoroughly, sand and dust off before finishing. If a finish is applied too soon after bleaching, surface defects will occur.
Recommended Products Are; There are a number of bleaching methods including using ordinary household bleach. You can also use a mixture of peroxide with full strength ammonia, however it isn't very user friendly, and it is rather toxic.
The most common bleach for use on timber is Oxalic Acid
Oxalic acid is purchased in crystal form from your chemist, paint supplier, chemical suppliers or hardware shops.
[edit] Surface Preparation & Application
Surface Preparation:
On new timber all surfaces to be bleached, should first be dressed all round and medium sanded with 180-240 grade sand paper. Remove all sanding dust and make sure timber is thoroughly free from any pencil marks, oil, wax or any other foreign substances. On paint stripped items, the bleaching process can follow immediately after the stripping process, while the timber is still wet. If this is not possible and the timber has dried, it is best to lightly sand the timber as explained above before bleaching.
Application:
The Oxalic crystals are dissolved in water that has just boiled, add crystals until you get a saturate, ie. no more of the crystals will dissolve. This solution is applied hot and left on until the desired result is attained. It is then neutralized by washing down with vinegar or with copious quantities of water. When the desired lightening is achieved and thoroughly dry proceed with the restoration or surface preparation of the timber.
Drying Times:
Allow to dry at least 72 hours if re-coating with singe pack products such as stains, clear lacquers, waxes, oils or shellacs.
If re-coating with two pack finishes allow at least one week to dry out the surface.
NOTE: If drying recommendations are not adhered to , various surface defects can occur to subsequent top coats.
Clean Up:
Clean all equipment using water.
[edit] Safety Precautions:
Remember that safety always comes first
As with any chemical safety precautions should be undertaken. We therefore recommend that you wear the appropriate safety items for your own protection, and observe safety instructions on packaging.
- Safety glasses.
- Rubber Gloves.
- Old clothes and rubber apron.
- Suitable footwear (waterproof).
- Working in a well ventilated area.
