Question: I recently purchased a house with a large redwood deck. The problem is that the deck has been spotted by greasy dog food in many places. Dishwashing detergent seems to have little effect on the stains. Can you help me with this problem?
Answer: Christopher Grover of the California Redwood Assn. in Mill Valley supplied details on two processes that should solve your problem. They're from a new data sheet, "Tips for Garden Projects," available free to readers of this column. All you have to do is send a self-addressed stamped envelope to the California Redwood Assn., 591 Redwood Highway, Suite 3100, Mill Valley, Calif. 94941 and ask for the data sheet.
To restore fresh natural redwood tones on a weather-darkened deck, scrub with a solution of trisodium phosphate--actually a strong detergent available at building or paint supply stores. Mix one cup with a gallon of water and use a natural or nylon bristle brush. Don't use a steel or wire brush.
If this doesn't work, or if there are nail stains, apply a solution of oxalic acid crystals dissolved in one gallon of warm water. Wear rubber gloves and eye protection. Allow the wood to dry and rinse with clear water. Once this dries, new finishes can be applied, just as you would on a new deck. Follow the instructions on the can of the appropriate deck finish.