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Advice for painting fiber cement or asbestos cement building shingles or siding. In our page top photo of badly peeling paint on fiber cement lap siding, we suspect that the wrong paint was used, the paint was improperly mixed, a primer was needed, or the paint was applied over a chalked or damp surface.
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Painting cement asbestos siding or non-asbestos fiber cement siding is in part a cosmetic decision. We have rarely seen this material in a worn, friable condition, but should that occur, one might paint the surface also to stop fiber shedding and to preserve the material.
Or you will have to paint if you are replacing broken fiber cement shingles in a wall that has already been painted. Otherwise the new shingles in their naked primer coat will stand out like a sore thumb. Our page top photo shows painted fiber cement shingles in a wall where we replaced broken materials.
And of course fiber cement products such as those sold hy GAF (Sources of Replacements for Asbestos Cement Shingles) come with a factory-applied primer intended to be "ready for painting".
Fiber cement shingles, both new non-asbestos product and the older asbestos-cement product are provided from the manufacturer with a coated surface, usually white. When the asbestos cement siding is soiled or moldy or has an algae coating we prefer to gently clean the surface with a sprayer, perhaps a deck cleaner solution.
Watch out: If you use a power washer (ASBESTOS CEMENT SHINGLE POWER WASH) be careful to spray "down" (to avoid blowing water into the building walls) and to keep far enough away that you do not damage the siding or "rough it up" which may cause more rapid deterioration or even fiber or asbestos release.
And before re-painting be sure that the surface is adequately dry. Latex type paints are a bit more tolerant of slightly damp surfaces than alkyds, but in no case should paint be applied to a wet surface, nor to a surface on which the primer has not thoroughly dried. Making either of those mistakes is likely to lead to a paint adhesion failure or to paint blistering. Details are at PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
(Other problems caused by high-moisture in fiber cement siding are detailed at SIDING, FIBER CEMENT MOISTURE LEVELS.)
But sometimes the asbestos cement or fiber cement shingles just look soiled and do not clean up enough to satisfy the homeowner. In general, this siding material can be painted using normal house paints. Check with your paint suppliers because some paints may not be recommended for the surface.
Be sure to use both a primer and top coat that are recommended for use on cleaned fiber cement siding as recommended by the manfacturer of both the siding and the paint.
Then be sure that the siding is dry before applying either primer or paint.
Watch out: But once you paint the fiber cement or asbetsot cement siding, you've converted a "no maintenance" surface into one that will occasionally need to be re-painted for cosmetic reasons. On a home we maintained for nearly 20 years, the factory-applied original coating endured perfectly well whereas neighboring homes of the same age and using the same siding but that had been painted required re-painting from time to time.
Paint Failures on Fiber Cement Siding: Factory Coating Failures vs. Installer-Applied Paint Coatings
Paint failures on fiber cement lap siding might be divided into two groups: failure of a factory applied finish coating (rare in our experience), and failure of field-applied paint coatings on bare or factory-primed fiber cement siding.
The peeling top coat on the siding shown above (Rhinebeck, NY) shows a white primer remaining in place on the fiber cement siding. Significantly this paint failure was observed only on the lowest course of lap siding on the building. The peeling siding was installed at the bottom of a wall in an alley into which drained roof eaves.
Reader Question/Comment: Delamination or Paint Failures in factory finished fiber cement siding
One of the main ingredients of fibre cement siding is cellulose. Where the product is exposed to direct or indirect water, snow or ice, the possibility of the fiber cement siding absorbing moisture exists.
This may cause the siding to swell, crumble or result in loss of paint adhesion. The core raw material of fiber cement siding is grayish in colour. When delamination occurs, it is easy to see these areas in contrast to the painted finish. - Hugh Cairns, Subject 2 Inspections, Email: firstname.lastname@example.org, Tel: 250-808-5777
Mr. Cairns is a Canadian home inspector located in B.C. and is an occasional contributor to InspectAPedia.com. Also see his photographs at AMERICAN CEMWOOD ROOFING.
Reply: diagnose the cause of paint failure; protect fiber cement siding paint coatings from early failures
Thanks for the comments, Hugh. The manufacturer, e.g. James Hardie, points out that their product must be protected from moisture prior to installation and that improper jobsite storage can result in product shrinkage and shrinkage gaps after installation.
Certainly one has to agree that the siding in your photos has undergone a terrible paint failure. Can you confirm that this was a factory-finished product, and can you confirm the product brand name? At SIDING, FIBER CEMENT MAINTENANCE we include details about steps to avoid early paint failures on fiber cement siding.
The actual siding board delamination problems we see seem to concentrate in hardboard siding products whereas in fiber cement siding boards I'm seeing and receiving reports of shrinkage, gaps, and coating failures.
A detailed report on that failure problem is found at SIDING, FIBER CEMENT GAPS.
If you can send along some sharp photos of actual fiberboard swelling and delamination, or if you can send me a siding sample, even a paint sample from the home in your photos, we'd be glad to take a close-up look in our forensic lab. Often a forensic microscopic examination of paint samples from a paint failure surface can tell us just why the paint is coming off of the surface to which it was applied.
For example, we can distinguish easily among adhesion failiures, paint over caulked surfaces, paint over dirt, and paint over primer that had not adquately dried. Simple microchemical tests can also quickly identify some basic paint incompatabilities between layers of paint coatings or between a paint and a primer coat.
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