Pressure Washing · Inspections

Pressure washing inspections

Inspect before, not just after. NPS guidance advises confirming that all mortar joints are sound and the building is watertight before any water cleaning, because otherwise water can seep through the wall and cause rusting metal anchors and stained, ruined interior plaster. After cleaning, check for granule accumulation in gutters and at downspouts, for stone grains or sand in the runoff, for damp patches inside, and for etched or grooved surfaces.

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Before the crew arrives. Walk the exterior and photograph it. Look at mortar joints, caulk and seals around windows and doors, any loose or damaged siding, and the general condition of wood. Any of these is a route for water to get inside. NPS is explicit that this check should happen before water cleaning starts.

Note what's already wrong. Dated photographs of existing chips, cracks and stains protect both of you. Without them, every pre-existing defect becomes an argument after the job.

During. The live test NPS gives for masonry is the runoff: grains of stone or sand appearing in the water on the ground means the pressure is too high. On a roof, granules washing into gutters and out of downspouts mean the same thing — and ARMA's position is that a pressure washer should not be on the roof at all.

After. Check inside as well as outside. Look for damp patches on interior walls and ceilings, particularly near windows and on the elevation that was washed. Check that windows and doors seal and operate as before. Check the gutters for accumulated granules. On wood, look across the boards at a low angle — grooves and furring show up in raking light when they're invisible head-on.

What to do if something's wrong. Report it in writing with dated photographs immediately, before anyone starts a second phase of work. This is exactly why you asked for a certificate of insurance and why you took the 'before' photos.

How to choose

Photograph everything before, with dates: Every elevation, plus close-ups of existing damage. It's five minutes and it settles most disputes before they start.
Check mortar joints and seals first: NPS advises confirming the building is watertight before water cleaning, or water seeps through and damages interior finishes.
Watch the runoff during the job: Stone grains, sand or shingle granules in the water on the ground means damage is happening now. Stop the work and ask.
Inspect inside afterward: Damp patches near windows and on the washed elevation are the sign that water got behind the cladding. Look within a day or two, not a month.
Report damage in writing immediately: Dated photos, by email, before further work. A verbal complaint at handover is very hard to prove later.

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FAQ

Pressure Washing inspections — common questions

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What should I check before a pressure washing crew starts?

That mortar joints are sound and the building is watertight — NPS advises exactly this before water cleaning masonry, because otherwise water seeps through the wall and can rust metal anchors and ruin interior plaster. Also check seals around windows and doors, and photograph existing damage.

How do I know if pressure washing damaged my roof?

Look for granule accumulation in gutters and at the base of downspouts. Granules are the shingle's protective layer — ARMA warns that pressure washing causes granule loss and very likely premature failure, and Malarkey notes the same about both washing and walking on shingles.

How can I tell if the pressure was too high on brick?

NPS gives a direct test: if grains of stone or sand appear in the cleaning runoff on the ground, the water pressure is too high. Afterward, look for etched or abraded areas and eroded mortar joints, which NPS notes allow increased water penetration and require repointing.

Should I check inside the house after washing?

Yes. Water forced behind siding or through unsound joints shows up as damp patches on interior walls and ceilings, especially near windows and on the elevation that was cleaned. Check within a day or two and report anything in writing with photos.

Sources

Where these figures come from

NPS Preservation Brief 1 — Cleaning and Water-Repellent Treatments for Historic Masonry (PDF) · retrieved 2026-07-26
ARMA — Algae and Moss Prevention and Cleaning of Asphalt Roofing Systems · retrieved 2026-07-26
Malarkey Roofing Products — Managing Moss and Algae · retrieved 2026-07-26
Polymeric Exteriors Association — Cleaning · retrieved 2026-07-26