Can you power wash asbestos siding?

Can you power wash asbestos siding?

A pressure washer is the wrong tool for asbestos siding, because its stream wears at the surface of a material that health agencies say should never be abraded. Asbestos-cement siding is safe to live with while it stays whole. The risk comes from work that breaks, sands or erodes it, and a pressure washer aimed at a brittle cement shingle does exactly that on a small scale.

In the US, the case against power washing asbestos siding rests on health-agency guidance about disturbing the material, and Michigan's rules on who may disturb or remove it are covered below. Gentle cleaning that keeps the shingles whole is the approach that fits that guidance.

What is asbestos-cement siding, and how do you recognize it?

Asbestos-cement siding is a hard, thin shingle or board made from asbestos fibers bound in Portland or hydraulic cement. The National Park Service history of these products says manufacturers promoted them as lightweight, economical and fireproof. Shingles were colored with pigments mixed in or rolled onto the surface, and pressed with textures such as a rough, rustic face or a pattern imitating weathered wood. The Minnesota Department of Health refers to cement-asbestos board siding by the trade name Transite.

Asbestos-cement shingles look and feel different from vinyl, aluminum or wood. They are rigid and brittle rather than flexible, and a broken edge shows gray cement inside. Many houses have them painted over. Newer fiber cement siding, such as the James Hardie product, can look similar, and the EPA says you generally cannot tell whether a material contains asbestos just by looking at it unless it is labeled. A sample analyzed by a lab is the way to know, and the EPA recommends a trained, accredited asbestos professional take it.

When is asbestos siding considered safe to leave alone?

Asbestos siding is considered safe to leave alone when the shingles are intact. The Connecticut Department of Public Health says in its 2022 fact sheet that the presence of asbestos shingles alone is not a problem when they are whole, undamaged, and not cracked and chalky. The Minnesota Department of Health says asbestos roofing and siding in good condition are best left alone.

Leaving asbestos siding alone means not disturbing it, not ignoring it. Any asbestos-containing material holds microscopic fibers that can be released when it is disturbed, according to the Connecticut fact sheet. The agencies list the activities to avoid: breaking, sanding, cutting, drilling and sawing (Minnesota), and sawing, grinding, abrading or dropping the shingles (Connecticut). The EPA adds scraping. Cleaning, painting and repairs all have to be planned around that list.

Why can high-pressure water damage asbestos-cement shingles?

High-pressure water can damage asbestos-cement shingles because it erodes the cement surface that holds the fibers in place. The Minnesota Department of Health notes that heat, water, weathering and aging can weaken siding that started out nonfriable, meaning it could not be crumbled by hand. Older shingles can also turn chalky at the face, and the Connecticut fact sheet leaves cracked and chalky shingles out of its not-a-problem description.

A focused stream cuts into that surface and can chip brittle edges and corners, which are the most exposed parts of each shingle. The cement and fiber that come off do not vanish. They land in the runoff, on the ground and on whatever the spray reaches, and the wall is left with a rougher, more open face than before the wash.

Western Australia shows what regulators there concluded about high-pressure cleaning of asbestos cement. Its Health (Asbestos) Regulations 1992 and work safety regulations prohibit pressure water cleaning of asbestos-cement sheeting. The state's guidance for local health officers says pressure cleaning can erode the surface layer and release fibers in a cement slurry that coats paving, garden beds, lawns, outdoor furniture, roofs and gutters on the property and next door. Once that residue dries, disturbing it can put fibers in the air. This is an Australian rule, not a US one, but the physical process is the same on a Michigan house.

How can asbestos siding be cleaned with low risk?

Asbestos siding is cleaned with low risk by keeping water pressure low and avoiding anything that scrubs or abrades the surface. The aim is to rinse dirt and growth off without removing any of the shingle. No US agency publishes a washing procedure for asbestos siding. The steps below are our reading of the agency lists of what to avoid, not an agency method:

1. Inspect first. Walk the walls and note any cracked, broken, chalky or loose shingles, and leave those areas alone.
2. Rinse at garden-hose pressure, from the top down, without aiming at shingle edges or joints.
3. Apply a mild cleaning solution with a low-pressure pump sprayer for dirt or mildew, and let dwell time do the work.
4. Skip wire brushes, scouring pads, stiff scrubbing and scraping.
5. Rinse again at low pressure, and rinse plants and walks so no residue dries there.

Can asbestos siding be painted, and how is it prepared?

Asbestos siding can be painted when the shingles are intact, and painting is common on older houses. The preparation is what changes. Two of the usual paint-prep steps, scraping and sanding, are on the EPA, Connecticut and Minnesota lists of activities to avoid, and power washing wears the same surface, so prep stays gentle.

Painting prep for asbestos siding means a low-pressure wash with a mild cleaner, a rinse, and enough dry weather for the shingles to dry out before primer, following the paint maker's label for cement-based siding. Loose paint is not scraped or sanded off the shingles. On a house built before 1978, the old paint on the shingles may also contain lead, which brings its own work practices. Our guide to washing a house before painting covers dry times and the order of work, and the post on washing a house built before 1930 covers lead-era paint.

What should you do if the shingles are cracked, chalky or broken?

Cracked, chalky or broken asbestos shingles should not be washed, scraped or patched by hand until a professional has looked at them. The Connecticut fact sheet ties the safe-to-leave status to shingles that are whole and not cracked and chalky, so damaged areas fall outside it. Keep people and pets away from broken pieces on the ground. The EPA says not to dust, sweep or vacuum debris that may contain asbestos.

A cracked or chalky wall calls for a lab test and a quote from an asbestos abatement contractor for repair or removal. In Michigan, EGLE's guide to the federal asbestos NESHAP explains how the rules are split. EGLE's Air Quality Division enforces the NESHAP, which generally does not cover privately owned residential buildings with four or fewer units. The Department of Labor and Economic Opportunity (LEO) runs the MIOSHA asbestos rules for workers, the Asbestos Abatement Contractors Licensing Act and worker accreditation, and EGLE notes that LEO requirements may still apply where the NESHAP does not. Contact LEO's MIOSHA Asbestos Program before any shingle comes off the wall.

Which Michigan homes are most likely to have asbestos-cement siding?

Michigan homes most likely to have asbestos-cement siding are houses built or re-sided before the 1980s. The National Park Service notes that asbestos-cement shingles and siding were produced into the 1980s. The Minnesota Department of Health says the use of asbestos in roofing and siding has declined rapidly since the early 1980s.

Asbestos-cement siding can also sit hidden under newer siding, because aluminum and vinyl were often installed over existing walls. That matters when an old layer comes off, since the first sign may be the shingles underneath. Our post on whether to wash, paint or replace aluminum siding covers that choice. For any siding job, Macomb Power Washing Solutions prices the work in a written quote, so mention possible asbestos when you request an estimate.