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Composite Decking Cleaning Guide: By Ryan Cash

Ryan Cash

UAMCC Associate Member
How do you clean composite decking?
Can I Use Bleach on a Trex Deck?
Is it safe to use high pressure on a composite decking?
Will pressure washing/soft washing void the warranty?

The most important thing you can do when cleaning a new substrate is to check with the manufacturer to see what their recommended cleaning process is. Their websites are typically chock full of information that can help.

By far, the most common composite decking material is Trex. So first, we're going to look closely at the right cleaning processes and guidelines

Per Trex guidelines: https://www.trex.com/customer-support/trex-owners/care-and-cleaning/

“A pressure washer with no greater than 3100 psi that has a fan attachment/adjustment and soap dispenser may be used to remove dirt or mud. Spray deck with soap, then follow by gently scrubbing each deck board with a soft bristle brush. Spray/rinse each individual deck board using a fan tip no closer than 8-in (203 mm) from the decking surface. RINSE THOROUGHLY. If dirty water from cleaning is left to dry, a film will remain on the decking surface.”

Then if you look deeper into their mold guide:

“All exterior building materials require cleaning. Trex is no exception. Periodic cleaning of Trex decking will remove dirt and pollen that can feed mold. If mold colonies appear, clean the deck with a commercial deck wash containing a detergent and sodium hypochlorite, commonly known as bleach. This chemical will remove the mold, but please be aware it will also lighten the wood on the surface”

And finally, when dealing with older styles of Trex:

“Trex does not recommend the use of a pressure washer. The use of a pressure washer on deck surface could damage the decking surface and will void the warranty with respect to any condition caused by the pressure washing.”

Different composites from different companies actually all require different types of cleaning. Talk to your customers about what type of decking they have and how old it is.

Once you’ve determined the recommended process, ALWAYS do a test spot before a full cleaning! (possibly underside of deck if you can).

In Addition to Trex, here's a quick guide for the top 8 brands of Composite Decking:

Bleach (SH)
Additional Notes
1500PSI @ 12” above deck​
Warm, Soapy Water recommended for cleaning​
No Pressure Washing​
Laundry Detergent without Bleach is Recommended​
Envision Composite Lumber​
1000PSI Max​
Oxalic Acid and Phosphoric Acids also ok for cleaning​
2500PSI @ 12" above deck​
PW not recommened if mold or mildew is present on deck​
1800PSI with a
20 degree nozzle​
Laquer Thinner and CLR can also be used for stubborn stains​
Moisture Shield​
1300PSI @ 10" above deck​
allow to age 3-6 months before any cleaning; Some products can lighten color of surface​
1500PSI Max for Rinsing only​
Sodium Metasilicate is a recommended alternative​
3100PSI* (No PW for older models)​
The use of SH can lighten the color of the decking​

Finally: to answer our questions.

How do you clean composite decking?

With a mixture of either soft washing, pressure washing, or a bucket and a soft bristle brush. Each brand and model has different cleaning instructions, so always check with the individual manufacturer and ALWAYS do a test spot first in an inconspicuous area.​

Can I Use Bleach on a Trex Deck?

Yes. However, the use of Sodium Hypochlorite may lighten the color of the deck. Always perform test spots before cleaning. Start with a light mixture and work up to only the strength required to clean.​

Is it safe to use high pressure on a composite decking?

Not Always. Each manufacturer has guidelines on the maximum pressure that their decking material should be cleaned with. Follow manufacturer’s guidelines to insure you are not going to cause damage​

Will pressure washing/soft washing void the warranty?

It absolutely can if you are cleaning and using processes outside of their recommended guidelines. Any damage that occurs when outside of their guidelines can and will void their warranty.​

Technical Documents and References to Cleaning Guides and Warranties