Cleaning Fiber-Cement Siding: Finish and Warranty Considerations

Two fiber-cement walls can look identical and answer to different instructions, because the finish decides both the cleaning rule and who stands behind the coating. A factory-finished plank — James Hardie’s ColorPlus or Allura’s Spectrum — comes with the siding maker’s cleaning bulletin and a fifteen-year finish warranty. A factory-primed plank painted on site comes with the siding maker’s primer, the paint maker’s instructions, and no finish warranty from the siding maker at all.

Establish which one you have before you choose a cleaner. It is the difference between working to a document that covers your coating and working to one that stops at the substrate.

The two finishes, and the document each one answers to

This page takes one of the claddings the siding and finish guide sorts. A factory finish is applied in a plant, and it is the product the finish warranty is written about. A factory primer is engineered to receive a topcoat, and that topcoat is somebody else’s product with somebody else’s instructions. The board is the same. The maintenance chain is not.

Hardie states that it “does not specify paint and will not warrant or accept liability for the performance of field applied finishes,” and its finish warranty excludes the performance of third-party paints and coatings. Its finishing bulletin still asks for a waterborne 100% acrylic exterior paint, a finish coat within 180 days of installation, paint or primer on every field-cut edge, and no stain, oil or alkyd paint and no powder coating. Allura’s care bulletin asks for a 100% acrylic waterborne primer or paint and prohibits the same coatings. Neither will warrant the result of that work; what both still warrant is the substrate beneath it, for thirty years.

On a factory finish, the warranty is real but narrow. Hardie’s fifteen-year warranty covers peeling, cracking and chipping, and pays a first-year paint and labor allowance of up to $2.15 per square foot that steps down 6.67 percent a year. Allura’s Spectrum warranty uses the same term, the same first-year figure and the same annual step-down. Both run from the date of purchase, both end after year fifteen, and both extend only to the first purchaser and the first transferee of the house — so on a house you are buying, the clock is already running.

What the two cleaning bulletins agree on

The current bulletins are closer than the marketing suggests, and their agreement makes a safe method easy to describe. The tools are a soft cloth, a soft non-metallic brush — horsehair, a chip brush, a soft siding brush — and a garden hose. Hard or metallic brushes and abrasive sponges are ruled out by both, because they can alter the finish. Plain water handles dust, dirt and chalking; mild liquid dish soap and water handles oil and grease; a proprietary mildew cleaner and water handles mildew, following that cleaner’s label. Both warn against harsh chemicals.

The sequence is the same in both documents: a small section at a time, starting at the top and working down, scrubbing side to side in the direction of the lap and up and down on panel siding, without pressing hard. Never let the cleaner dry on the board and rinse until none of it is left.

The prohibitions match too. Acid washing and abrasive blasting are not recommended by either maker, because both can damage the cementitious surface. Both attach the method to the warranty. Hardie writes that damage from improper cleaning or maintenance “may not be covered”; Allura writes that it “will not take responsibility for damage arising from improper cleaning and maintenance.”

The differences are detail. Hardie names Jomax, Mildew Check and Mold Armor for mildew, and publishes a separate supplemental bulletin for tough stains on ColorPlus only — clay, gypsum and cement mortar dust — with two named cleaners diluted 1:12, used within ten days of installation, and explicitly not for primed board. Allura names Jomax or Mold Armor for mildew and the same two cleaners at 1:12 for tough stains, and asks for a test on a small, inconspicuous area first.

The pressure question

Both makers permit a pressure washer, with the same three limits: a wide fan tip, a nozzle at least six feet from the wall, and pressure under 1,500 psi. That figure is a ceiling rather than a setting; pressure and chemistry divide the work differently. The question is not what the machine can do but whether the stream lifts dirt without lifting the finish. If the board was painted on site, the paint maker’s instruction governs and may be stricter.

The direction matters more than the number. Fiber-cement lap siding sheds water at the lap, and the lap is the detail the wall depends on. A stream aimed up under a lap is aimed at the joint that keeps the wall dry.

The wash, in order

1. Read the document for your finish. The maker’s current bulletin, not a dealer page or a forum.
2. Protect what is not being washed. Shield plants, cover what runoff would mark, and keep the stream off windows, doors, vents, fixtures and wiring.
3. Test an inconspicuous area. Allura asks for it explicitly; on an unknown coating it is the only way to see whether the method will damage the finish.
4. Work top down, in small sections. Clear the loose dust, scrub in the direction of the lap, and keep the section wet until it is rinsed.
5. Rinse until the water runs clear. Neither maker allows the cleaner to dry on the board.
6. Check the wall dry, then check the water. Mildew that returns is a moisture question, not a cleaning one.

What the finish warranty does not cover

The exclusions are more instructive than the coverage. Neither finish warranty covers damage from water infiltration; Allura’s names frost, condensation, moisture, standing water, snow and ice submersion. Neither covers mold, mildew, fungi or any organism on the siding — both say so expressly. Neither covers fading or chalking from normal weathering, and neither covers a lack of proper maintenance. What both do cover is excess color change beyond normal weathering: more than four delta E units within the first three years.

Those terms draw a line the reader can use. A green or dark film is a maintenance matter: cleaning removes it and satisfies the maintenance condition, but it never becomes a defect claim. Peeling, cracking or chipping can be a defect, but a claim has conditions. Hardie asks for written notice within 90 days of discovery, Allura within 30. Both want photographs, proof that you are a covered person, and no permanent repair before the maker has inspected; both state that repairs begun without prior authorization may void the warranty.

Efflorescence, the white powdery deposit that appears on cement-based products, is excluded by both. Allura treats it in a separate bulletin as what it is: soluble salts drawn to the surface by moisture and left behind when the water evaporates. It is a water story, not a dirt story.

Washington: the wall behind the board

Washington’s residential code says what a fiber-cement wall is expected to do, and its wording is worth knowing before a washer is pointed at one. WAC 51-51-0703 requires the exterior wall envelope to prevent water accumulating in the assembly by providing a water-resistive barrier behind the siding and a means of draining water that enters. Its third exception says the drainage requirement is not to be read as requiring an air-space cavity behind fiber-cement lap siding — and that a water-resistive barrier is required regardless. The same section requires fiber-cement lap siding to lap at least 1¼ inches and to be installed in accordance with the manufacturer’s instructions.

The consequence is practical: the lap and the barrier are the water detail, and the code does not require a cavity behind the plank to dry one out. Water pushed up under a lap has nowhere to go but inward. That is why the direction rule earns its place, and why a maker’s bulletin beats a machine’s pressure rating.

The other water on the wall does not come from a hose. Allura’s care bulletin asks for a minimum one inch of clearance from concrete, roof lines and patios and six inches from finished grade, keeps landscaping off the siding, and asks that sprinklers be adjusted so they do not saturate the wall, because water carrying rust or minerals can discolor the surface, shorten the paint’s life and encourage mildew. It also asks that drainage be corrected wherever water is retained against the siding. Those checks are made from the ground and they outlast any washing schedule.

When cleaning is the wrong response

• White powder that wipes off is chalking, which both warranties treat as normal weathering. Washing will not restore it; the coating is due for maintenance.
• Peeling, flaking or checking is a coating failure — a repaint or a warranty question, not a cleaning job.
• Soft, swollen or delaminated board, or water appearing inside the wall, means the assembly is wet. Stop and find the water first; water at the base of a wall is its own diagnosis.
• Mildew that returns within weeks means the wall is staying wet. The growth is the symptom, not the cause.

If you hire the work

A written scope should name the finish on the board, the cleaner, the pressure limit and nozzle distance if a machine is used, and the rinse — plus what is excluded: no acid wash, no abrasive blasting, no repair. Comparing those scopes line by line is more useful than comparing totals, and what drives a total is its own subject.

The next useful step

Find the document before you find the nozzle. Photograph the wall dry, from the ground, in flat light; note where it is chalking, where it is peeling and where the growth returns; then read the bulletin for your finish and the warranty that came with the house. If the board is field-painted and you have no paint record, the paint maker’s instructions are the ones to find — and the best time to establish that is before a washer is on the wall.