Cedar shake roof prep

What’s a good simple mix to clean/prep cedar shake before oiling.

Sodium hydroxide- is generally what I use just looking for others expertise.


Hey Jordan-- Our first residential job this year is coming up and it’s a Cedar shake house. We always use a hydroxide mix on these houses now with an Oxalic bath afterwords and then rinse rinse rinse. These jobs pay in the thousands and they are my favorite residential customers. High end houses never have vinyl and some villages won’t even allow a homeowner to have vinyl siding when your talking hi end area’s. Vinyl is an easy clean but in reality it’s just imitation clapboard.

My Opinion is to stick with the hydroxide on shakes and always always always use a brightener such as a citralic but in our case we go one up on that which is an Oxalic acid and we get paid well for this service.

Our core clients all have cedar roofs.

We have avoided pressure washing them at my preference, due to safety and not wanting to get into stain, shake replacement.

Now that we have a vehicle dedicated to pressure washing and wanting to grow that side of the business I am considering opening the doors. Scare the tar out of me. Look forward to following this thread, as I hope to pick some things up from it.

Actually have to decide tonight if I want to take on a job or pass it on to the guy I have been for years.

It really depends on the condition of the cedar shakes. If they are weathered and gray then you would use a cleaner. Most people will use either an oxygenated bleach cleaner or a chlorine bleach based cleaner. As John alluded to some people will add sodium hydroxide to the mix. If you use sodium hydroxide it will be a shorter dwell time in these cases. If the shakes have excess mold, moss, lichen, etc, you will probably use chlorine bleach because you need immediate results so that you can come back to oil. If it is real heavy we also will scrape and brush surfaces first. After we clean the roof we apply oxalic acid to all surfaces to brighten wood, remove iron stains, and neutralize the alkaline cleaner or stripper used. Oxalic works best at removing iron stains and citric acid will not remove these stains. When rinsing these heavy built up surfaces you will need to use a pressure washer with low pressure to effectively remove all surface issues, soft washing will not help in these situations when a customer wants the shakes coated very soon after restoration. The key is dwell time, very low pressure, and a 40 degree tip. Use larger orifice 40 degree tips to reduce pressure or a dual lance wand will work well in these situations too. Regardless of what you use there are always 4 basic rules to wood restoration that certainly apply to cedar shake roofs as well. First you pre-wet all surfaces, water is also a barrier and allows your cleaning solution to work on the surfaces rather than soak in and become even more difficult to rinse off. Secondly, apply your cleaner or any chems and products. Third, rinse, rinse, and rinse again. fourth, apply a finish. If you ever need to, you should replace and repair shakes prior to the cleaning process. When I do these jobs I educate the customer on the maintenance of the shakes and how important it is to keep up with a program. I then give them a ballpark maintenance price and time of next service before I leave.


Great info guys! What is a good ratio to mix the oxalic at? I’m use citric acid currently at 2-3oz per gal. And how much dwell time is safe?

Again thank you

We generally use Oxalic acid close to full strength(can’t remember how many oz/gal since my guys do this now). We do what Everett says in the above post(excellent post I might add) where we spray it on when done with the cleaning and watch the shakes magically brighten up before our eyes(most amazing thing to see in all of Powerwashing) and then we rinse all the shakes again.

A word of caution. Oxalic acid is very strong on the lungs. I suggest to wear a mask when applying it. Yrs a go one of my workers didn’t wear a mask and the spray went down wind and hit him head on. He had such a bad reaction that he was hospitalized for 4 days. Oxalic is greatnubt it needs to be respected when in use.


8oz. - 16oz. per gallon of water on the oxalic. 8oz, usually gets it done. Also depends on how you are applying it.

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Thank you John, Dave and Everett! That is great info and always nice to learn new tricks to the trade.