Can you pressure wash LP SmartSide siding?

Can you pressure wash LP SmartSide siding?

LP SmartSide siding should not be pressure washed, according to the company that makes it. LP Building Solutions tells owners to avoid using a pressure washer on SmartSide because high-pressure washing can cause moisture intrusion, discoloration and damage to the paint. Its care and maintenance sheet, revised in May 2024, repeats the rule inside its cleaning steps: rinse with a garden hose on a low-pressure spray, and do not use a high-pressure power washer.

The tools LP names instead are a soft brush, cloth or sponge, a solution of water and mild detergent, and a garden hose or a handheld or backpack-style pump sprayer for the rinse. Some siding makers publish pressure limits instead of a ban, so a house with SmartSide walls needs its own line in any washing plan.

What is LP SmartSide, and how is it different from fiber cement?

LP SmartSide is an engineered wood siding, which means wood that LP treats and binds with waxes, resins and zinc borate for strength and for resistance to fungal decay and termites. It comes primed for paint or, in the ExpertFinish line, with a factory-applied color. LP also makes SmartSide in Michigan: its mill in Sagola, in the Upper Peninsula, pressed its first SmartSide board in March 2023.

Fiber cement, the material in James Hardie siding, is a cement-based board. Both products are painted, both are hung in overlapping laps with caulked joints, and from the sidewalk they look much alike. The difference sits under the paint. A wood-based board can take on water wherever the paint film or a cut edge is left open. That is why LP's care sheet asks that every exposed bit of wood substrate stay sealed with paint or caulk, and why nearly every other rule on that sheet aims to keep water off the boards.

How does LP say to clean SmartSide?

LP's cleaning method for SmartSide is a low-pressure rinse, a hand wash with mild detergent and a second low-pressure rinse, done one small section at a time.

1. Rinse a small section with a garden hose on a low-pressure spray, starting at the bottom of the wall.
2. Wash it with water and mild detergent, applied with a soft brush, cloth or sponge, working from the bottom up.
3. Rinse right away with a garden hose or a handheld or backpack pump sprayer on low pressure, before the solution dries, until no soap is left.
4. Spot clean and rinse any missed areas, then move to the next section.
5. Touch up bare chips with matching paint on a cotton swab, on the bare spot only, and let it dry at least 24 hours.

LP's reason for working from the bottom up is streaking: soapy water running down over dry, dirty boards can leave clean tracks. The sheet also says never to use harsh or harmful chemicals that can damage the paint or the siding, so a stronger cleaner is not a shortcut around the brush.

Why does high-pressure water risk moisture damage and paint failure?

High-pressure water risks moisture damage on SmartSide because lap siding is built to shed water falling down the wall, not water driven up into it, so a forced stream can reach wood behind the laps, at butt joints and around nail heads that the paint was meant to keep dry.

Paint failure follows from the same force: a narrow, close stream can lift paint at edges and joints, letting rain reach the wood. LP's own list of results from pressure washing is short: moisture intrusion, discoloration and paint damage. The upward-spray mechanics are covered in our post on whether pressure washing can damage vinyl siding.

How do you remove mildew from shaded SmartSide walls?

Mildew on SmartSide comes off first with LP's routine wash: a low-pressure rinse, mild detergent on a soft brush, and a thorough rinse. LP's care sheet asks owners to keep the painted surface free of mold, mildew and algae, and when the yearly check turns up mildew, it says to remove it and to contact the paint manufacturer for guidance. LP also notes that ongoing contact with water can cause discoloration, shorten paint life and stimulate the growth of fungus and mildew.

For mildew that detergent does not lift, LP's mildew guidance for SmartSide gives one mix: five parts water to one part Simple Green concentrated cleaner and degreaser, applied with a sponge to the mildewed areas and rinsed with a low-pressure garden hose. LP's ExpertFinish care sheet uses the same mix from a pump sprayer before a repaint, left on for 10 minutes without drying. For anything stronger, LP points owners to the paint manufacturer. Shaded walls grow the most, for reasons explained in our post on why one wall of a house stays green.

Which parts of the siding need a yearly check?

LP asks for a once-a-year inspection of SmartSide, with special attention to the bottom row of siding, the area under the windows and any uncaulked gaps. The bottom row takes rain splash and snow, and the boards under windows take runoff from the sills above. The checks LP lists are below, and they are easiest right after a wash, since clean, dry boards show hairline paint cracks and open caulk joints that dirt and pollen hide.

• Paint: inspect for damage to the surface and repaint before the existing paint fails.
• Joints and seams: replace cracked or missing caulk with a non-hardening, paintable sealant that meets ASTM C920, minimum Class 25.
• Mildew: remove any growth, with guidance from the paint maker.
• Flashing and gutters: repair damage and clear blockages so water drains away freely.
• Drip caps: keep the 3/8-inch gap above drip cap flashing open, since LP says not to caulk it.
• Dents and gouges: fill with caulk of the same ASTM class, then prime if required before painting.

How does maintenance tie to the LP SmartSide warranty?

The LP SmartSide 5/50-year limited warranty ties coverage to installation and maintenance. LP describes a five-year, 100 percent labor and material replacement feature and a 50-year prorated material replacement feature after that, and it covers hail damage up to 1.75 inches in diameter on siding that is properly installed and maintained. The care sheet states the link at the top of the page: warranty remedies are not available if its instructions are not followed, and those instructions include the no-pressure-washer rule.

A simple record helps if a question ever comes up: dated photos of each yearly check, receipts for repainting and caulking, and a note of how the siding was washed. LP says incorrect installation voids coverage only for the damage it causes, and the full terms depend on the product and installation date.

How does caring for LP SmartSide compare with James Hardie?

LP SmartSide and James Hardie siding are both painted lap boards, and both makers tell owners to skip the high-pressure washer, but their cleaning instructions differ in the details. The table compares LP's 2024 care sheet with James Hardie's 2024 cleaning tips. Hardie's own rules are covered in more depth in our guide to cleaning James Hardie siding.

How do Michigan snow banks and mulch beds affect the bottom course?

Michigan snow and mulch both work against LP's clearance rule for the bottom course of SmartSide. LP asks for at least six inches between the siding and the finish grade, and says not to let garden mulch or other debris build up and compromise that clearance. It also asks for a slope of 1/2 inch per foot away from the house on every adjoining surface, including porches, patios, driveways, walks and grade.

A Macomb or Oakland County winter tests that rule. Snow cleared off a walk or driveway often ends up piled against the nearest wall, where it can sit against the bottom boards for weeks, melting by day and refreezing at night. Pile snow away from SmartSide walls where you can, and check the bottom row for paint damage each spring.

Spring mulch is the other common cause, since a fresh layer each year raises the bed until the bottom course sits in mulch that stays damp. Rake beds back from the wall before adding new mulch, and aim lawn sprinklers away from the siding, since LP's care sheet says sprinklers should not spray directly onto trim and siding.

For a SmartSide house, Macomb Power Washing Solutions prices house washing from $349. The itemized written quote comes within 24 hours, and travel is free across all 87 communities in its service area.