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About cement Asbestos siding:
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1940s construction boom, a wider variety of colors became available,
including a spackled look, where the colors were impregnated throughout the
sheet so they would not powder or peel off. When color change became
desirable after installation, owners were encouraged to paint the
asbestos-cement products. It was the “attractive home safeguarded with
modern asbestos siding, fireproof, rot proof, termite proof” idea that
intrigued many Americans during this era. By 1950, approximately one billion
square feet of asbestos-cement products had been produced for use in the
building industry.
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| By the time the Environmental Protection Agency (EPA) was established in
1970, the commercial world of asbestos-cement products had expanded into
many markets. Annual use of asbestos-cement in the United States continued
to climb for another three years before reaching the peak of its popularity,
only to plummet to a quick death in 1973 when the EPA implemented the
initial ban on asbestos. Asbestos-cement products are still produced in a
few countries outside of the United States and are considered a beneficial
resource; however now they carry the label “hazardous material” and not
“miracle mineral” as they once did.
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| Asbestos-cement products were developed in an era of ingenuity for
creating easy to install and economic building materials. Although
asbestos-cement has acquired a poor reputation by association of its title,
it has not gained that reputation through a lack of durability or utility.
In order to preserve this twentieth-century material, understanding what
makes, or does not make, asbestos a hazard is truly important. In this case,
no hazard is created when asbestos-cement building materials are sound and
left in place, or when treatments incorporate non-abrasive means.
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ASBESTOS REGULATIONS:
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Some asbestos fibers, when inhaled, constitute a health hazard leading to
asbestosis, a form of lung cancer. These health risks prompted the
establishment of strict environmental regulations on working with asbestos.
Health risks were shown to be greatest during mining and production
processes, but minimal during installation and use of asbestos-cement
products. According to the EPA, a material containing asbestos is deemed
potentially hazardous only in a friable state, which means when it can be
crumbled, pulverized, or reduced to a powder by hand pressure.
Asbestos-cement is not considered friable, and therefore not hazardous,
because the cement binds the asbestos fibers and prevents their release into
the air under normal use conditions. However, asbestos-cement products are
classified as friable when severe deterioration disturbs the asbestos or
mechanical means are used for chipping, grinding, sawing, or sanding,
therefore allowing particles to become airborne.
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CONSERVATION:
| Due to the abundance of buildings clad in asbestos-cement products, and the
low health risk of the non-friable material, it is necessary to know how to
preserve and rejuvenate the material back to a vibrant and usable life. The
primary conservation options for asbestos-cement building materials are to
maintain and manage in place, repair, replace in part, or abate. The level
of deterioration determines the appropriate option to be employed.
Abatement, including full removal or encapsulation, should only be used as a
final course of action.
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Maintain and Manage:
| Deterioration of asbestos-cement is inevitable, as is eventually the case
with most all materials. Maintenance procedures can decelerate
deterioration, such as conducting visual inspections to evaluate condition,
keeping the material clean, making minor repairs as necessary, and
organizing treatment practices that minimize the extent and impact on the
material. Also, it is important to maintain the environment that surrounds
the structure and protect the asbestos-cement materials. Examples of
protective measures include the planting of shrubs or flower beds between
the skirt of the wall and lawns to protect from lawnmower damage, adding a
bumper material to the bottom row of siding to reduce vulnerability to
cracking and chipping, and keeping branches and debris away from the roof
and out of gutters.
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Repair:
| When repair is the necessary treatment for a deteriorated asbestos-cement
product, the least amount of material should be discarded and the most
possible amount of original material should be retained. The type and extent
of material deterioration associated with asbestos-cement products depends
on the cause of the distress and therefore requires investigation and the
tailoring of a solution for each case. When repairing the deteriorated
materials the gentlest means possible should be used following applicable
asbestos regulations, along with repair techniques sympathetic to the
existing fabric.
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| Asbestos-cement is inherently a brittle material with low impact resistance,
so even with the added reinforcing given by the long thin asbestos fibers,
the material is susceptible to cracking and chipping as generally induced by
low impact forces, repeated cyclical loadings, or deteriorated fasteners. In
addition to this primary deterioration tendency, manufactured
asbestos-cement products can potentially discolor, erode, spall, flake, form
efflorescence, and create an environment for biological growth. Guidance for
repairing asbestos-cement products is given here for these several distress
manifestations.
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Cracking:
| If a crack forms from either impact or fatigue and mandates repair, several
techniques can be used depending on the size of the crack. For hairline
cracks, work clear epoxy into cracks with a thin object. Epoxy can be
susceptible to UV attack and may need to be restored periodically by
removing and replacing. For slightly larger gaps, use a grout of Portland
cement and water, mixed to a flowing consistency, and tinted to match. For
cracks greater than an eighth of an inch, use a thicker grout consistency or
add sand to the mix. The crack may need to be widened to rake out the loose
material. Soak the crack with water, then trowel patch the grout into it.
Keep the repair damp for a week to promote slow and proper curing and reduce
shrinkage
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| If the fasteners for the asbestos-cement product have become deteriorated or
have broken from corrosion, they should be replaced with a more durable
metal. Various metals can be considered for the replacement, but should be
compatible with the sheathing. Stainless steel is generally recommended
because of its superior corrosion resistance. Fasteners such as nails should
be long enough to hold the materials securely (self-clinching nails can help
with this).
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Discoloration:
| Discoloration of asbestos-cement products stems from a build-up of surface
contamination (such as soiling), stains produced by leaching of other
material byproducts (such as corrosion run-off), or a direct change in color
due to the environment (such as ultra-violet sun bleaching). These
discoloration occurrences typically result from normal weathering, but
indicate a chemical reaction that may decrease the strength or durability of
the material when neglected over time.
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| Discoloration should be removed from the asbestos-cement products, and
cleaning recommendations generally suggest trying several solutions of
varying strengths. After evaluating the results of the trials select the
alternative that provides the needed results while using the gentlest means
possible without causing adverse reactions to the substrate. Mechanical
methods for cleaning can promote asbestos fibers to become airborne,
therefore should only be used following asbestos regulations.
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| To clean light stains, such as dirt, the asbestos-cement products should be
washed with a detergent solution or a mixture of one half cup of trisodium
phosphate dissolved in a gallon of hot water. Rinsing with plenty of clear
water helps to remove all trace of the cleaning solution. Start the cleaning
at the bottom of the wall, working upward in small sections, rinsing
immediately, and keeping the shingles below wet, otherwise, dirty water can
drip down over dry surfaces and leave streaks almost impossible to remove
later.
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| Recommendations for stains such as rust, are to dissolve one part of sodium
citrate in six parts of commercial glycerin. Mix part of this with inert dry
clay, such as diatomaceous earth, to form a poultice and apply as a thick
layer. When the paste is dry, replace with fresh paste or moisten with the
remaining liquid. Complete removal of the stains may require a week or
longer. A ten percent oxalic acid solution has also been found to
successfully remove rust from cementious products. If the substrate, metal
fixtures, or other adjacent objects are causing staining they should be
cleaned and coated or replaced.
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| If the stain cannot be removed, another option is painting the
asbestos-cement products. Painting is an especially good solution if the
material was originally painted, but adds a maintenance factor. Oil based
paints and varnishes are not chemically compatible with cementious
materials. High quality alkali-resistant and weather resistant exterior
paint (i.e., 100% acrylic coating) should be used on exterior
asbestos-cement materials, or use pigmented shingle stain. Before being
painted, asbestos-cement surfaces should be cleaned, then primed with an
alkali-resistant primer.
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Eroding, Spalling, or Flaking:
| Erosion removes cement particles and can result in the release of asbestos
fibers, leaving the material with less reinforcement. Due to the high
density, low permeability, and low porosity of the material, this tendency
is virtually unnoticeable. However, erosion can become a more serious
problem under regular and extremely harsh weather conditions. If intense
erosion occurs, the durability of the material can be compromised.
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| Although rare, spalling or flaking occurs when elements permeate beneath the
surface of the asbestos-cement material and then expand, causing a portion
of the material to be released due to the resulting stress. As the moisture
content increases, more severe deterioration can occur. This deterioration
is more likely to occur in products that were cured at lower temperatures
and therefore are more vulnerable to water penetration.
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| To control eroding, spalling, or flaking, chemical consolidants and/or
breathable sealers (most commonly silane) can be applied to strengthen the
material while adding water protection. Testing is critical since
consolidants and sealers can promote spalling if water is getting in through
the backside of the material. |
| A grout or latex-patch may also be considered, but must be compatible with,
and typically softer than, the asbestos-cement material to form a good bond
and not promote increased spalling. This repair procedure can be tricky and
may lead to constant patching, and may be unsightly if not done with extreme
care. For these types of deterioration tendencies, the material may be
better off left alone or partially replaced.
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Efflorescence:
| Efflorescence appears on many Portland cement products that are exposed to
weathering. This form of crystalline growth indicates that water is passing
through the material, which can promote deterioration of the
asbestos-cement, in addition to making it unsightly. Generally this is seen
at the beginning of the material’s life, where rain and weathering tend to
remove it over time.
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| To clean efflorescence deposits, the surface should first be dry brushed
with soft bristles, not scratching the surface. If efflorescence still
remains, test to see if it is water soluble or acid soluble. If water
soluble, the wall should be wiped with a wet sponge or brush (a light
detergent can also be added). A hose can be used, but spray the water in a
downward direction as perpendicular force will drive the efflorescence back
into the material. If acid soluble, clear ‘white’ vinegar, acetic acid,
phosphoric acid, or similar proprietary products diluted in water should be
used. It is recommended to wet the surface with solution, then apply
solution more liberally on the asbestos-cement. After two or three minutes,
scrub using a fiber brush with more solution, then rinse extremely well with
clear water. Safety precautions provided on the product labels should be
followed, and again tested before commencing extensive application as
adverse effects or discoloration may occur. Pitting from chemicals will
increase dirt buildup and water permeability, decreasing the durability of
the material.
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Biological Growth:
| Biological growth on the exterior of asbestos-cement can be a problem in
sheltered environments or on northern exposures. Shade trees located close
to a building can shield sunlight and result in prolonged dampness of the
asbestos-cement building product and promote biological formations, such as
moss and algae. Not only are the growths unsightly, but they can stimulate
surface disintegration, dissolution, and staining.
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| The presence of moss and other fungi growth signals that the moisture
content of the material is high and therefore an attack by a more damaging
biological species could occur. It is not only important to remove the
growth from the asbestos-cement material, but also to remove the environment
that is causing the growth. To eliminate biological growth, a strong mixture
of weed killer and water could be tested. If unsuccessful, a solution of
four parts bleach, one part trisodium phosphate, and twelve parts warm water
is recommended. After a week or so when the moss has turned brown and dry,
it should be brushed off. In the case of ivy this technique is sometimes not
helpful in removing the thousands of tiny roots left after the ivy has been
pulled off; a stronger product may be needed (i.e., copper sulfate). It is
important to remember that biological growths differ widely and so do the
processes for their removal. Testing various products and selecting
appropriately is highly encouraged |
Replacement:
| Since asbestos-cement products were manufactured in standard sizes, shapes,
colors, and textures, partial replacement is well suited for implementation.
This process is acceptable when part of, or pieces of, the existing
asbestos-cement building material have deteriorated to such a degree that it
is much more feasible to replace than repair. Since the United States no
longer produces asbestos-cement products, an alternative material should be
selected to match the original. Some materials that have been manufactured
to replicate asbestos-cement building components are non-asbestos reinforced
cement, fiberboard with asphalt, fiberglass, metal, and vinyl. For the
purposes of preservation, one of the non-asbestos reinforced cement products
is most appropriate.
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| Many varieties of non-asbestos reinforced cement or fiber-cement are
currently available. Fibers that have been introduced with cement include:
steel, glass, polypropylene, wood (these four being the most common),
acrylic, Akwara, alumina, carbon, cellulose, coconut, Kevlar, nylon, perlon,
polyethylene, rock wool, and sisal. Combinations of fibers are currently
undergoing research in order to get properties closely matching those of
asbestos. Several companies manufacture products that replicate
asbestos-cement roofing and siding shingles, flat sheets, and corrugated
sheets. Some of these manufacturers include: Supradur Manufacturing Company,
Cement Board Fabricators, U.S. Architectural Products, Inc., Re-Con Building
Products, and GAF Materials Corp. The fiber-cement products replicate the
size, shape, thickness, and structure, along with texture and color of many
of the asbestos-cement products previously available. Where color matching
is not found, an alternative is to replace in size and shape then paint over
the entire structure for a uniform appearance. In addition, the hardware and
the installation procedures for these products are similar to those for
asbestos-cement products due to their similar characteristics and
proportions.
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