How to Pressure Wash a Composite Deck How to Pressure Wash a Composite Deck

What You'll Need
Pressure washer
Composite timber cleaner
Spot cleaners
Covers for plants etc
Coarse sand paper

To pressure wash a composite deck requires a little preparation. These composite timbers are a little different to ordinary wood and require some preparation.

Step 1 – Basic Cleaning

Remove all the dirt, leaves and other debris that has accumulated over the period. Move the furniture off the deck to give you a clear working area. You are going to need to use a proprietary cleaner for the composite wood so you need to protect any plants, bits of lawn or concrete paths that might be affected by it. Give the deck a good rinse with water.

Step 2 – Spot Cleaning

Where furniture has stood, a collection of leaves has lain, or whatever there might be stains that need to be removed. Clean these stains thoroughly with whatever the appropriate cleaner is. If you are not sure about a particular stain, try to test the cleaner where it will not show.

Step 3 – Apply the Composite Deck Cleaner

The deck cleaner will come with specific instructions for use and you should follow these carefully. The cleaner has to sit on the composite deck for a prescribed length of time and then washed off with a pressure washer. For this reason you will work on small sections of the deck rather than try to do the whole lot at once. Using less than 800psi wash the cleaner off along the grain of the deck. Keep the spray moving and don’t spray from too close to the deck.

Step 4 – Repeat the Process

Repeat the process until you have cleaned the whole of the deck and the railings.

Step 5 – Rinse

Use the pressure washer to rinse off the whole deck.

Step 6 – Dry and Check

Give the deck a couple of days to dry completely and then check for any stains that did not get cleaned away. These can be left but you should be able to clean them with coarse sand paper. If it seems easier you can try a wire brush but some composite timber reacts badly to metal and it could end up worse. Test it in an area that doesn’t show. You can also ease out scratches and dents the same way.

Step 7 – Replace the Furniture and Uncover the Plants

Once the deck is cleaned you can replace the furniture and uncover any plants, lawn or concrete that is still covered.
Provided you have used the correct composite timber cleaner the results should be excellent. For the future it might be a good idea to introduce some preventive measures.

Get rid of light mildew with a composite cleaner specially formulated to do that job. If mildew is developing you know that there is a problem to solve because the mildew cannot grow without food.


Even if your deck looks clean it could be starting a good collection of debris so just give it a wash down with clean water every so often. This could be the only cure necessary to stop the mildew.

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