Concrete Dust on New Cedar

Hey guys, we have a customer that just built a new cedar pergola and stone patio. The contractor got concrete dust everywhere when they were cutting the stones. They are looking to have us wash the pergola, patio, and side of the house to get rid of the concrete dust.

It already feels like the concrete dust is sort of set up and stuck to the horizontal surfaces on cedar pergola. I am definitely concerned about our guys even getting remotely close to the brand new cedar even with low pressure tips.

Is there a solution we can use to “soft wash” off the concrete dust? I am not opposed to having our guys brush something on and lightly rinse if needed. Thanks for any suggestions!

Just my thoughts, dry concrete dust and water make wet concrete that is permanent. Make more money walking away.

Thanks for the fast response! I just added some pics FYI. Passing was my first thought. They are a good regular customer and their pergola is really nice so I would like to try to help them out if possible and I am sure they would pay for a job done right. My biggest concern though is not to damage anything.

My first thought was: They don’t have a blower or a shop vac or an air compressor?

Then my next thought was: This seems like a lose-lose-lose situation. Lost time, lost money, lost customer when it doesn’t turn out.

I’d probably try to blow it off for them for free if they were good customers, but I wouldn’t wash it and I wouldn’t spend more than 15 minutes on it.

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Yes, it would have been great if the contractor would have just blown everything off after they finished cutting. Unfortunately, I think the dust might have settled up to the point where it is past being able to be blown off. It did not seem to want to come off real easily when I tried brushing it off with my hand. I did explain to the customer, that the only way we would consider doing it is if we could find a way to remove the concrete dust without creating any damage to the wood (which is why I am running it by you guys).

There might be a chemical to mix with water that doesn’t allow the concrete to cure. If it’s just dust from them cutting stone, then it shouldn’t harden with water since it doesn’t have a hardener in it correct?

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Light sanding.


The contractor wont take care of his own screw up?

Hit it with a 800 - 1000psi tip in your pressure washer. Try a little section and see. Should be fine. Are they going to stain? If so you’re definitely good to go. I think the pressure will work fine, if not the sandpaper alternative best suggestion.

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If they are planning on staining it, sanding will not be helpful with absorption since it closes off the cells. I do everything I can to avoid pressure washing cedar but sometimes the customer or the last person to work on the fence doesn’t leave me a choice. That said, keep it under 1500 psi and make continuous passes from one end of the board to the other if at all possible. Stay about a foot off the wood and it shouldn’t do anything as long as you keep the wand moving. That will also blow the dust off and not allow anything to set up, just keep someone washing the concrete underneath it while you are rinsing it to ensure the wetted dust doesn’t settle there. You also need to explain to them what you are doing and that there is some risk involved but that if you don’t get it off and it rains all of this is moot. Good luck.

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Thanks for all the replies guys!

Apparently the cedar already has some type of stain on it. I guess they built the pergola first and then added all the stone work later. I think the dust has sat on there for at least several weeks, so it has been wet already. Maybe the stone dust will not be as stubborn as cement dust? Having the stone contractor clean it up is probably not the best idea with as nice is that cedar is. I can just picture them blasting everything off with 3 or 4 thousand psi.

I think maybe our safest bet would just be to downstream some elemonator on it, brush everything with a soft brush, and then give everything a light rinse with a soap tip staying a good distance away from the wood. Do you guys think throwing a gallon of white vinegar in with our soap mixture would cause any issues with the wood? I have read about using vinegar to clean up cement and was thinking that might help a little in this case.

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Well the customer called and wants to go ahead with the job. I estimated it at about a half day’s labor. I put the following notes on the estimate as sort of a CYA.

-Service includes washing concrete/stone dust off east side of house and pergola.
-Service also includes hand cleaning outside of windows on east side of house.
-Cedar will be cleaned by applying a soap solution and brushing all horizontal surfaces (including top of pergola).
-Only very light pressure spray will be used on cedar to avoid disturbing the appearance.
-Highly acidic or caustic cleaners will not be used.
-We expect a majority of the concrete dust will clean off the cedar. There is a possibility there may be staining or residue left over due to dust that has cured on the surface. This will need to be addressed with the stone contractor as sanding and restaining might be required to correct the issue.

Will let you guys know you it turns out.


We got this one done this week. No pics because it was still wet when the guys left and it looked great while wet. Called the customer after it dried for a day and he was super happy.

We ended up mostly brushing on a mixture of soap, white vinegar, and water. The pressure washer probably would have got the job done with just a light spray but this house had the worst water flow we have ever seen. We could only use the machine for short periods of rinsing. It all worked out though. We were done in about 2 1/2 hours. Probably would have been 1 1/2 if it wasn’t for the water pressure issues.