Hey, Andy! The first thing you need to determine is what sealer is on the deck. Is it oil or acrylic or something else?
If the owner can identify the sealer (or even better if he has the can) look for words like linseed, acrylic, alkyd, etc. If you can't find that info, look for phrases like "cleans up with soap and water" (water-based sealer like acrylic) or "use mineral spirits" (oil-based sealer like linseed). This will help you pick a stripper to remove the old finish.
If there is no telling what sealer it is, try using a strong caustic stripper on a small spot. If you apply the stripper and the sealer begins to turn to goo within, say, 5 minutes, then you have an oil sealer that will be relatively easy and inexpensive to strip. If it does not, then you likely have a tough strip job on your hands (water-based sealer).
Once you decide what it is you are taking off, you can treat the redwood much like any deck wood. It has a lot more tannins, so it will turn absolutely black as you clean it. Brightening is even more critical on redwood.
As for choosing cleaning products and sealers, stick with whatever quality products you are familiar with. I always prefer to use an oil over a water-based sealer. If you want some specific product suggestions or are looking for better products or a better supplier, call us. We have been selling one of the most complete line of products for more than a decade.
