Composite deck cleaning

ok i was washing some homes in neighborhood today a guy walked up and wanted me to look at his deck

it is 10 ft wide x 16 ft long

it is composite blueish color has black mold spots he tried bleach and jomax but said it wont get it
I tried some sh and it seemed to clean a little but still had darker color spots
i put a little pressure on one board of step and it took color off but seemed to come back after it was wet again
Any ideas what i can do to clean it

I usually just hit them with a strong house wash and rinse it off with a 40’ tip two boards at a time. I know some people just use strong HW a truck brush and a garden hose to…

By using a PW you can void the warranty of the deck. Be careful of how you sell to the customers. Explain that you can clean the deck. Kind of like the difference between soft washing and power washing.

Low pressure & a house wash mix. I used high pressure on a friends ( it was old & he was replacing it soon ). At the end of the job there were piles of sand all over the place. That’s what it does to the surface. It was also rougher.

John Devine.

[MENTION=5210]Washed Up[/MENTION]

I use a strong HW mix and a stiff nylon bristle brush, sit for 10 min and rinse

I ended up using straight sh and then rinsed with water hose came out good thanks

Thats what I was going to say to do. When I was involved with the Trex class action lawsuit around 8 yrs ago some of these older Trex decks were covered in black mold spots. One of the decks I cleaned I soaked it 3 seperate times with SH to where it finally came clean. Most of the other decks were easy. Soaked them in a SH mixture & then rinsed clean. $1.50sq’ to clean them from Trex because they lost the class action lawsuit was a homerun.

Many of the composite companies use wood content in them as well. For instance, what John T. is referring to was the original TREX which was Red Oak which is a hard wood that leaves a dark black tannin. Anyone who has had to clean off oak leaf stains from concrete can attest to that. Composites should be cleaned the same way as a wooden deck to remove over 90% of the black stains. Bleach will take care of the mold and mildew and the oxalic acid brightener will neutralize the tannins stains. This is the main reason they lost their first lawsuit, because they were not completely honest with the public about the black stains. It was also recommended to them that even if they used 1% wood in their formula they should recommend sealing. They used about 50% red oak and did not recommend sealing. The issue was further compounded when folks started pressure washing the surfaces and removing the cream coating which further exposed the wood content leading to more black stains. This is when they came out with “pressure washing may void the warranty” as Rob alluded too. Bottom line, older TREX, TimberTech, and other wood content composites should be bleached and brightened.

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A house wash mix with low pressure works for newer trex, but I’ve used up to a roof mix on some trex decks that were really nasty (lichen growth).

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I contacted TREX and they recommended Olympic Deck Cleaner and no pressure washing.

The customer is aware of the TREX issue. We will work a small test area to see the results.

1 gallon covers 300 sq.ft… Breaking it down to a 5 x 5 test area would give me 12 attempts to see if the Olympic Premium Deck Cleaner will work.

I will report back on this test.

Until then, could you guys explain the some terms you used in the thread?

Please explain HW - House Wash - What cleaner is this? Mix Ratio
Please explain SW - What cleaner is this? Mix Ratio
Please explain Roof Mix - What cleaner is this? Mix Ratio

Thank you in advance for any information you will share.


They used to recommend Corte Clean and I am not sure when they started recommending Olympic but either way you are paying for overpriced bleach. Olympic is sodium hypochlorite which you are better off getting 12.5% and that way you can make it stronger if necessary, you can’t with the Olympic brand. Typically what happens with these is someone has already pressure washed them taking the coating off the surface and exposing more of the wood content, again the older generations of Trex, so the mold and mildew becomes very difficult to get of with weaker solutions because it imbeds in the rougher surface. In my opinion, you get a better result much easier by not listening to them on the solution. They are towing the company line with their recommendation although I agree with not using the pressure washer on the older Trex. No matter the composite you should always check the warranty of the product so that anything you do will not void the warranty and expose you to any action down the road. I make no guarantees on Trex because even they now it will not be 100%.

This is my understanding from reading the boards. I use a high draw injector with straight 10.5% Sh and surfactant, for almost everything with no problems

We normally us strong HW mix…1 1/2 gal SH 3 1/2 water …apply with soft bristle deck brush…dwell and agitate any bad areas…rinse with garden hose or very low pressure…at time we do ds strong hw mix dwell and rinse to clean it up…just depend on how bad they are

If you are making your own solution then how are you addressing the tannin bleed from the wood content in the old Trex or other products made with ANY wood content? To do this correctly you also need to follow up with oxalic acid which will neutralize the tannin stains. The black spots are not all mold and mildew. This is one of the items that led to the lawsuit.

Ralph, you put on straight up 12% and DS it and have had no color issues? Did it get rid of the black spots?

Eric Calabrese
TopNotch Powerwashing & Sealing
Stirling NJ
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Eric, I’m not sure what your question is. I think I was trying to explain the different mixes that people are talking about on these boards. I don’t do roofs, so my main method is DS’ing is straight 10.5% and elemonator for almost everything I do here in Florida. You might not get away with that in New Jersey though. The algae/mold/mildew here is intense, and the stronger mix doesn’t seem to hurt grass, paint, etc. Not sure what you mean by color issues. As for black spots, if you are referring to the little black spots on concrete underneath the algae and mold, yes it comes off with a straight SH (1 maybe 2 coats) and a little bit of dwell time.

Hey Ralph, sorry. I was referring to applying, via ds, 10.5% plus detergent onto a composite deck? You have not had a discoloration issues? Did it kill off more of the mold spots?

Eric Calabrese
TopNotch Powerwashing & Sealing
Stirling NJ
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I wasn’t talking about composite decks. I was answering Jack Robinsons question about different mixes people just throw out. Most people know what they are, but if you are a total newbie it can get confusing. I am an old school deck guy I don’t use SH on any deck. There are basically no decks here in FL anyway!. When I do run across a composite deck I use Sodium percarbonate.

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I gotcha, do get Precarb locally or via Bob?

When I have a composite deck or wood dock lined up, I buy the sodium percarbonate from ebay, and mix it with oxy-clean laundry detergent for the surfactant. You can get any chemical in bulk from ebay.