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Sheathing Celotex Homasote & Other
SHEATHING, FOIL FACED - VENTS
SIDING TYPES, INSTALLATION, DEFECTS
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STAIN DIAGNOSIS on BUILDING EXTERIORS
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STAIRS, RAILINGS, LANDINGS, RAMPS
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STUCCO WAll FAILURES DUE TO WEATHER
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STUCCO OVER FOAM INSULATION
STUCCO PAINT FAILURES
SURFACE GRADING, SITE DRAINAGE
Thermal Expansion Cracking of Brick
TREES & SHRUBS, TRIM OFF BUILDING
TRIM, EXTERIOR CHOICES, INSTALLATION
VINYL Siding or PLASTIC Window ODORS
WATER BARRIERS, EXTERIOR BUILDING
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WINDOWS & DOORS
Fiber cement siding home: this article discusses the selection and best-practices installation of fiber cement building siding products. In a series of companion pages we provide details about the properties of various fiber cement siding products from the major manufacturers, how to identify fiber cement siding, how to install fiber cement siding including guidelines for gaps, clearances, nailing schedules, end and cut sealing, siding joint or abutment caulking, painting or staining. We include descriptions of the field performance of fiber cement siding products and a detailed field investigation of several product failures: of fiber cement stain or coating peeling and cracking, and of gaps, shrinkage, and loose, buckled fiber cement siding.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
This article series discusses best practices construction details for building exteriors, including water and air barriers, building flashing products & installation, wood siding material choices & installation, vinyl siding, stucco exteriors, building trim, exterior caulks and sealants, exterior building adhesives, and choices and application of exterior finishes on buildings: paints, stains.
This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Page top photo of fiber cement clapboard installation courtesy of Carson Dunlop Associates.
Details about an older generation of fiber cement products, asbestos cement wall shingles and modern fiber cement wall shingles are discussed separately at SIDING, ASBESTOS FIBER CEMENT. Also ASBESTOS CEMENT ROOFING and also CORRUGATED ROOFING.
Many synthetic alternatives to wood siding have fallen short either on aesthetics or durability.
Fiber cement building cladding has been around for more than 60 years, if we include its early form, cement-asbestos shingles such as those on the home shown at left (Dover Plains, NY). Following the development of concern for asbestos safety, fiber cement shingles continue in production, but using reinforcing and filler materials other than asbestos.
Fiber-cement [in plank form], unlike it's shingle ancestors, is one of the newest entries into the siding field and holds promise in that the material can be fashioned to resemble almost any exterior cladding, holds paint well, and is essentially impervious to decay, insects, UV radiation, and fire.
Modern fiber cement siding products are also very dimensionally stable and resist shrinking and swelling, cupping, warping, and splitting. Warranties run from 30 to 50 years depending on the manufacturer and specific configuration. Fiber cement siding is cost-competitive with vinyl and hardboard siding and significantly less expensive than premium wood sidings.
Older fiber cement and asbestos-cement wall siding (photo at left) is vulnerable to impact damage. Repairs must be done with care to avoid breaking additional siding shingles when removing and replacing the bad ones.
Modern fiber-cement is made up primarily of Portland cement, sand, and wood fibers. It is chemically similar to older asbestos sidings but contains no asbestos, glass fibers, or formaldehyde.
It does, however, produce a very fine silica dust when cut with a saw or abrasive blade, which, if inhaled, can cause silicosis and other serious respiratory problems.
Fiber-cement boards are extremely straight and rigid when held edgewise, but they are much heavier than wood—about 20 pounds for a 12-foot length of 8-1/4 -inch siding.
They are flexible along the flat dimension, however, so any lumps in a wavy framing job will tend to telegraph through the siding. The material is fairly brittle and, if not handled carefully, can crack.
Styles and Sizes of Fiber Cement Siding Products
Fiber-cement is available in a wide array of styles and finishes modeled after other materials ranging from horizontal wood siding to vertical sidings, wood shakes, bricks, and stones. The wood patterns are generally available either smooth or wood-grained and most are available factory-primed or finished as well as unfinished.
Our photo (left) is interesting because it shows two nearly-identical fiber cement wall shingles. The shingle on the right is a new replacement product that does not contain asbestos, while the shingle on the left is an older cousin that contains asbestos. A clue to the presence of new fiber cement shingles on this home might be the observation that the shingle on the right is coated only with the factory primer while that on the left has been painted a few times. See ASBESTOS CEMENT SIDING for details.
Fiber-cement horizontal siding planks are typically 5-1/4 to 12-1/4 inches wide by 12 feet long and are designed for a 1-1/2 inch overlap. Vertical siding panels measure 4x8, 4x9, or 4x10 feet, and shake and shingle panels are typically 16x48 inches. The thickness of most siding materials is 1-5/inch. Smooth and textured soffit and trim boards are also available.
Fiber-cement soffit material is typically 1/4-inch and most trim stock is 7/16-inch thick, but manufacturers have recently introduced thicker profiles (see section on fiber-cement trim, page 34 in Best Construction).
Lap-Siding Fiber Cement Board Installation
Fiber-cement siding products install similarly to the wood products they imitate. They can go over wood-based sheathings or rigid foam, but they must be nailed or screwed directly to studs or 2x blocking. Fasteners should penetrate solid wood by 1 to 1-1/4 inches, depending on the manufacturer’s specifications.
Our fiber cement siding photo (left) courtesy of Carson Dunlop Associates, shows the product in end view (trade show booth installation detail) and includes the first-course bottom spacer behind the fiber cement clapboard.
The 12 foot long fiber-cement planks can be held edgewise by a single person, but the boards may break in two or deform if picked up flat. One person can install a plank by driving a single nail near its center to hold it in place against guide nails driven into the sheathing to mark the upper edge.
Manufacturers recommend leaving 1/8-inch between board ends and window casings and trim and caulking with a paintable 100% acrylic latex caulk. Butt joints between two planks can be either lightly butted and painted over or gapped 1/8-inch and caulked. Manufacturers recommend priming cut ends on site if the joints are not being caulked. As with other siding products, leave at least 1/2-inch clear at step and other flashings so the bottom edge does not soak up water.
Nailing & Butt-Joint Flashing Details for Nailing Fiber Cement Siding
Our photo (left) shows a pre-fabricated plastic flashing device intended to be inserted at the butt-joints of fiber-cement wall siding. (Photo courtesy Carson Dunlop Associates.)
Fiber-cement siding should be nailed directly to studs with nail penetration into solid wood of 1 to 1-1/4-inches, depending on the manufacturer’s specifications.
Pre drilling is required within 1/4inch of an edge or near sharp angles or other fragile shapes to avoid cracking. Pre drilling may also be required when nailing through foam sheathing to avoid cracking the siding.
Manufacturers require a hot-dipped galvanized or stainless-steel siding nail (or roofing nail for blind nailing) that should be driven flush with the surface.
Overdriving of nails can cause the material to shatter around the nail, weakening its holding power and, with some products, voiding the warranty. Staples and clip-head nails tend to penetrate too far, but coil nailers with adjustable depth-of drive work well. Some contractors hand-nail the siding to avoid problems.
Given the longevity of the siding, a long lasting corrosion-resistant nail is recommended. If fastening to metal studs, use corrosion-resistant pneumatic pins or self-tapping bugle-head screws.
Standard Nailing in Fiber Cement Siding
Blind Nailing Procedure for Fiber Cement Siding
Cutting Methods for Fiber Cement Siding
Ordinary carbide-tipped blades produce less dust but wear out within a few hours compared to a few months for abrasive blades. In the last few years, manufacturers have responded with specialized diamond tipped blades and tools, making the work easier and safer.
The new fiber-cement blades cut smoother, create less dust, and outlast ordinary carbide blades. When used with the new dust-collecting saws designed for fiber-cement, cutting is safe and effective.
Many contractors also use electric shears such as the fiber cement shears produced by Malco Products. (Photo above courtesy Malco Products.)
Fiber cement cutting shears are similar to a sheet-metal nibbler but specially adapted for fiber-cement. These make a clean cut with little dust, but are not as fast as a circular saw and cannot cut through multiple boards at once. Scoring and snapping, as for drywall, is also an option for quick cuts where a crisp edge is not needed.
Finishing & Painting Details for Fiber Cement Siding
After installation, small dents or chips can be filled with any cementious patching compound. Before priming or applying the top coat to pre primed material, wipe away any dust from cutting with a damp cloth or sponge or lightly hose down the siding and allow it to dry thoroughly.
If the siding has been hosed down or power washed (unprimed siding only), allow at least two sunny days before priming. Painting should be completed within 90 days of installation to avoid deterioration of the surface from prolonged exposure to water.
For unprimed siding, manufacturers recommend an alkali-resistant, 100% acrylic primer specifically approved by the paint supplier for fiber-cement. Back-priming is not necessary; in fact, some manufacturers recommend against back-priming so any trapped moisture can dry from the back of the siding.
For the top coat, use a 100% acrylic latex paint. Because fiber-cement is dimensionally stable and largely inert, it holds paint well. Estimates range from 7 to 15 years for a quality paint job. Some of the prefinished products carry 15-year warranties on the finish.
Our photo (above left) of paint failure on a fiber-cement siding installation was provided by BC home inspector Hugh Cairns. Mr. Cairns is a Canadian home inspector located in B.C. and is an occasional contributor to InspectAPedia.com.
Details about fiber cement siding installation, gaps, caulking, flashing, sealing, are at
The illustration below is of a Chinese-made fiber cement siding product produced by Ningbo Yihe Greenboard Co., Ltd. While we have no specific complaint about this product, it and similar fiber-cement siding board products may add to difficulties in determining the origin and manufacture of various modern fiber-cement siding products.
The siding above is described by the Zhejiang manufacturer as:
Watch out: That fiber cement siding is available from a variety of sources is evident from the list below. In addition, some our investigations of fiber cement siding failures (paint or coating failures, shrinkage, gaps discussed at x and x) led to an assertion by U.S. manufacturers that even though the homeowner had been told that a U.S. product was being installed (Hardieplank for example) in fact the manufacturer has told the homeowner that it was not their product. If this is indeed confirmed to be the case, building owners may be paying a premium for counterfeit products and more, when there is a product failure they may have no recourse.
Identification of Chinese-Made Fiber Cement siding may be aided by this additional detail offered by the manufacturer: beginning in 2012, fiber cement siding from the supplier listed above is provided only with a smooth finish. The embossed wood grain patterns that were used before 2012 have, according to the manufacturer "been mostly destroyed".
However in the spring of 2013 the company contacted us with this update
-- Adapted with permission from Best Practices Guide to Residential Construction.
Frequently Asked Questions (FAQs) about fiber cement siding products, installation, troubleshooting, failure diagnosis
Question: 1/4-inch gaps between siding boards and next course?
How tight should the 5.25" (4" reveal) lap boards rest one on top of the other? For a new install, I would expect the bottom of the board to lay flat on the top of the one under it, however, on a job, I am seeing boards with 1/4"+ gaps, but I can't find any literature saying what the max should be. - Mike 3/13/2013
Normally they are touching to 1/16"
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: email@example.com, 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.
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?
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 HARDIEPLANK SIDING GAPS though I have to add that just today (3/20/13) we learned that James Hardie has now told the homeowner that the siding that failed on their home is not Hardieplank.
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. Over at PAINT ANALYSIS, DIAGNOSTIC USES we discuss the sorts of paint failures we've been able to confirm by sample analysis in the lab.
Questions & answers or comments about installing fiber cement siding on buildings.
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