Re deck. Two bds. replaced. New benches/railings built on site. Proper aged pressure-treated wood not used. Buckling repaired. Used diff. stain from what was on deck. Didn't seal; said in case wanted to change color later. Problem: mold which powerwashing w/clorox and other things doesn't remove. Only thing that has worked but labor and time intensive, and I have a disabiity, is Cascade powder d.wash. deterg. and much work. Comes back. Want to seal so deck isn't constantly stained and we don't use. GOOP was recommended. Neither Home Depot nor Lowe's has heard of it. I've had it in the past myself. Suggested GOO which I have but this isn't for big job like cleaning deck. I want to get cleaned and put something on that will repel for at least a yr. or two. Never had this prob. before (many yrs.). Will hire someone if can get good plan to clean and seal. I'm not concerned w/changing color. Deck high off ground w/large storage area underneath so lots of decking which is okay. Only w/in last 2 yrs. has mold/mildew been problem. One "...." suggested putting ceramic tile down on a deck w/natural backyard and we own two lots behind that are wooded.