Cedar shake chemical advice

I tested yesterday on my cedar shake with 6-8 percarbonate and rinsed and applied a second coat rinsed and sprayed oxalic to balance. All 12v application. I tried spraying up close to rinse but it was pilling wood. Rinsed from 5 ft away. I checked the wood for stain and didn’t find any but now that it’s clean I think there was some old left over. My shingles are 40 years old and we’re dirty. Many shingles are darker at the bottom now. What do you guys recommend. Did I use the wrong chemical. What could I have done to get this better? Trying to understand what chem to use when on cedar.

When I use sodium percarbonate on decks I have to scrub most of the one ones with any growth whatsoever. It’s just not aggressive enough for heavy growth. Google “3 stepping wood”. It calls for adding 2 oz of sodium hydroxide per gallon to the sodium percarbonate. Apply with a 12v. Then neutralize with oxalic or citric acid.


Got it. I have some f-18. So that’s 2 oz per gallon f18 on top of the 6-8 of the f-8 percarbonate per gallon? Now, if I understand correctly, the hydroxide alone is good for stripping stain or sealer but added to percarb enhances cleaning of really moldy cedar.
Is the job I did clean enough for a customer? Just not sure how perfect you need to get it when it looks that bad to start. I’m curious if anyone thinks this had sealer on it? Some shingles looks like it did, but not many. Figure it would have been more uniform if it had been sealed

I would put more emphasis on whether the job is clean enough for YOU rather than a customer. Customers opinions will always change from one job to the next, and that is where setting expectations comes in. If you feel you did the best job you could do for them, you’re done. if you feel the job could be better but you didnt charge them nearly enough for all the work you are going to have to do, take the hit, do the work, and charge more next time. Every job teaches you a lesson.

Expectation wise, you now know to tell a customer that there will be some areas ( in my short cedar experience, low down on the north facing walls and also sometimes right under a soffit or an eave) that will appear a bit darker than the rest. This is the nature of wood, and no two shakes are exactly the same.

Having said that, i personally would not be 100pct happy with the results you achieved and would reapply and depending on the results, work on giving those areas a little TLC in the form of a medium bristle brush. They may not come perfect but will look a lot better. Also, since it is your house, its the perfect time to experiment with different ratios and cleaners, scrubbing vs not scrubbing, 800 psi vs 1000 psi rinse, 6 inches away vs 8 inches away, etc


Thank you for the advice and honesty on my test run. I was not completely happy with it but was unsure if I could have done better. From your advice, I see, I could do better and will. Gonna give my plants a few weeks before hitting anymore chems on them. I have another test house to do with cedar. I’m going to add a little hydroxide this time and try a closer rinse and experiment with the brush. I’ll post results with the fine tuning. Thanks for posting


I’m curious what the cedar pros think in regard to cleaning the double size cedar like I have vs the smaller thinner shingle shakes. Is there a difference to approach with chemicals since the smaller ones are much thinner and delicate? I have a test house, same cedar and soil level as mine to do soon. It had been sealed many years ago so i hope the 3 step does better than my results. Do any of you guys advise to treat with sh first to get bulk growth off then 3 step at a later date? Is that just overkill.

By no means am i an expert but i can tell you pretreating with SH will probably be a waste of your time. The mold and mildew will just peel right off when you rinse at 800ish psi.

Just did some cedar today where there was a bush up against the house and the cedar behind was HEAVILY green with mold and mildew. After I prewet and used 12v to apply slightly over 3oz/ gallon of F18/dwell for 10 minutes (I go to the worst spot on the house and try the chemical at a low dilution first), it still looked green. But as soon as I hit it with that little bit of pressure, it all came off with no issues.

I have not had luck with percarbonate on wood, its just a little too gentle. I also havent tried adding hydroxide to it, and given my results with straight F18 followed by oxalic, i dont think id ever bother, the hydroxide works well enough as a cleaner on its own. But again, Im no expert and i have never done a side by side comparison.

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