How to Clean James Hardie Siding
A garden hose and half an hour, once or twice a year. That’s most of it. Here’s the method and the things to avoid.
How often
James Hardie’s care guidance suggests rinsing the siding every six to twelve months. In Calgary a spring rinse after the road dust and gravel season, and another in autumn before the snow, works well. Walls near a gravel lane, a busy road or a construction site may want it more often.
What you need
- A garden hose with an ordinary spray nozzle.
- A soft brush or soft cloth. A car-wash brush on a pole is ideal.
- A bucket of water with a little mild dish soap for stubborn spots.
The method
- Close the windows and check that exterior outlets are covered.
- Wet the wall from the top down.
- Work in sections you can reach. Brush gently along the length of the boards, not across them.
- Rinse each section from the top down before the soap dries.
- Rinse plants and windows below when you’re done.
Pick a mild, overcast day if you can. On a hot wall in full sun, soapy water dries before you can rinse it and leaves marks.
What not to do
- Don’t use a high-pressure washer. James Hardie’s guidance advises against it. High pressure can damage the finish, force water behind the boards and blow out caulking.
- Don’t use harsh or acid cleaners, solvents or abrasive pads. They can dull or strip the finish.
- Don’t use a wire brush or anything that scratches.
- Don’t spray upward under the laps. Siding sheds water coming down, not water driven up.
Specific problems
Dust and dirt. Water and a soft brush.
Grease or oil, often near a barbecue or kitchen vent. Mild dish soap in water, a soft cloth, then rinse well.
Mould or mildew, usually on shaded north walls or behind shrubs. Use a mild cleaner suitable for painted exterior surfaces, following its label, and rinse thoroughly. Then deal with the cause: trim plants back and improve air flow.
Sprinkler marks. Hard-water spots come off with gentle washing if caught early. Re-aim the sprinkler so it stops hitting the wall.
Splashed mud along the bottom. A sign that soil is too close. Rinse it off and check your clearances.
Use the wash as an inspection
You’re already looking at every wall, so check for cracked or missing caulking, chips, loose boards, soil or mulch against the siding, and gutters or downspouts spilling onto the wall. Small things caught now are cheap to fix. See repairs.
Upper storeys
A hose from the ground reaches most two-storey walls for a rinse. Don’t brush from a ladder unless you’re confident and have someone holding it. If the upper walls need more than a rinse, hire someone with the right equipment and tell them not to use high pressure.
Full upkeep checklist: maintenance guide.