Left to right: No treatment, Sodium Hypochlorite (1/2 rinsed with oxalic), Sodium Percarbonate, Sodium Hydroxide.
Summary: All 3 looked similar. The bleach treatment looked slightly lighter in color, while the Hydroxide/Perc were almost exact color. Hydroxide had significantly more furring, shorter dwell time might reduce it. Biggest surprise was how much of a difference an oxalic rinse made on the bleach treatment.
SHypochlorite panel… left side from black tape back had no oxalic rinse, right side did. Side that oxalic was used on looked significantly better:
Close ups of furring. Perc and bleach had essentially no furring, except for a slight amount on two or three boards of the perc treatment. Those boards were overall darker in color too, so not sure what the deal was with them.
Bleach:
http://imgur.com/df8Wka7
Perc:
http://imgur.com/4z7fvk4
Hydroxide:
Final thoughts: For this particular fence, all three looked acceptable color wise (except for the non oxalic rinsed bleach treatment). Hydroxide and Perc looked best to my eye, with bleach close behind. May try hydroxide with shorter dwell time to see if it reduces furring.
If i had to pick just one method, based on my results with this particular wood, i would probably pick SPercarbonate. Nice color, no furring, safer for landscaping. I havent figured up cost comparisons, though.
Details:
(Note: Dwell times were a little longer than i had planned, because i did them all at once, instead of one at a time.)
Sodium Hypochlorite: 1.5% mix (109 oz water, 19 oz 10% bleach, 1 oz roof snot). Dwell time 18 minutes. Oxalic rinse on half.
Sodium Percarbonate: (Wolmans Deck Brightener) 1 cup into 1 gallon hot (tap) water. Dwell time 19 minutes. Oxalic rinse.
Sodium Hydroxide (Roebic Drain Crystals): 1/2 cup into 1 gallon hot water. Dwell time 18 minutes. Oxalic rinse.
Rinsed with 2510 tip on 4GPM machine - around 650 PSI. Oxalic mixed 1 cup to 1 gallon hot water.
