How to clean a stained deck. Help!

I have a chance to clean my first deck. It’s stained already and not too dirty. Some bird crap, light dirt and algae. I read several threads on this and there are so many conflicting opinions on this topic. Some guys say no SH at all and some guys say SH with this chemical and don’t use this chemical and the next guy says its ok and it’s getting confusing trying to sort it all out. Anyway its a stained deck and looking for some new opinions and hoping the more experienced guys can lead me in the right direction. Thanks in advance for any advice!

I would use a very weak SH solution - perhaps 1% hitting the surface. This is due to the algae.

I just did a fairly large composite deck and used .5 gal SH to 4.5 gal water and some surfactant. Direct applied with a 12 v system. Dwell 10 minutes and like pressure rinse. I even had a soft bristle brush to hit the areas where the algae was more concentrated.

Be sure not to confuse tree pollen with algae this time of year. Around these parts, our oaks put out a bunch of pollen the will look like green algae on a deck.


how many days should you wait to stain the job after the wash job is done, to get the best results???

I typically wait at least 24 hours. You really want the wood to have a moisture level of less then 15%. Really has to do with humidity and temperature. High humidity and low temps (60’s - 70’s) may be wait 2 days.

Just did 750 ish linear feet of fence. Cleaned on Wed, it rained on Thursday, dried Friday and stained Sat and came out great! It was 85 degrees on Friday.

Ok thanks Mike! Ya I used to live in South Florida and everything turned yellowish green down there about mid March or so. Thanks for the info! Should I pre wet first?

I won’t do any more decks, can’t seem to get the desired result. For some reason the green algae just doesn’t die no matter what. Plus the customer is wanting a ‘power wash’ of the cracked, peeling deck paint/stain so they can stain again. Yikes.

I just sprayed chem, dwell and rinse. It was a composite deck. I think I posted before and after pics on another thread- There was some algae for sure but also quite a bit of just oak pollen.

Edit - keep in mind, composite decks are not like regular wood decks. Composite decks have wood and plastic fibers in the construction of the “boards” so it is more like washing vinyl that actual real wood deck.


I’ve used both sodium percarbonate and sh and the sh cleans better. You just have to make sure you rinse really well. I had to brush the percarb to get it to look as good as the sh. It just didn’t want to get the algae up. Percarb is more mild so it definitely has its place.

Either way I would still neutralize and brighten with oxalic. It makes a big difference.


Reviving this thread a year later, I have these decks to prep for a re-stain, has light dirt and algae growth. I’m Planning to use a house mix on it and really light pressure to rinse the crud off. Do you think the SH ontop of this stain would cause any issues? Thanks guys

Will the SH at that dilution alter the coloration of the deck as SH does on regular wood? Have a composite deck lined up, now that dirty, but I’m worried about discoloration due to the wood fibers in it.

Is this a serious concern to have or will the SH not have any effect at that dilution? By the way I plan on applying with a 2 gal pump-up sprayer (it’s a really small square deck)

Trex deck I did with a 2% house wash mix. You will be fine. Just explain to the customer that the wood fibers inside the Trex or composite will lighten a little with the cleaning

For $150 I’ll tell you how to do it, LOL.

Seriously, you’ll need a little stronger for the bad parts, like 1-1.5% let dwell about 10min and that should do it, Hopefully they’re going back with same or slightly darker color. It will lighten in places.


Is that your minimum too? :joy: I appreciate the reassurance, looks like my head was in the right place!

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Here are the results from the wood cleaning ! I was super nervous as this was a big project for me. Paid well too! I learned a lot from this and I’m happy I did it


Ready for stain


Excellent work :+1:, amazing how it all turns out when you just dive in a give it a crack.

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Looks great! :smile:

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Looks good