Caring for natural stone
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Findstone |
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Stone
Types | Considerations
| Environment
| Preventive
Maintenance |
| Preservation
| Restoration
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This
report is a short summary and general guide of maintenance
recommendations and processes which have proved practical for
many stone surfaces over the years. It should not be assumed
that any particular process description or recommendation is
suitable for any particular project or situation without
qualification. There are many variables which must be
considered when designing a maintenance program including:
physical properties of the stone, abrasion risk, hostile
factors in the environment, the maintenance budget and the
skill of the maintenance personnel. It is highly recommended
that a maintenance professional be consulted if there is any
doubt about whether or not a specific method or product is
safe and effective.
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Stone
Types |
Marble
Composition:
Calcite, Calcium Carbonate
Hardness: Soft
Absorption: Oil, Water
Limitations: Absorbs
oils and other liquids, easily scratched, acid sensitive
Sealer: Penetrating type siloxane or
fluoropolymer
Cleaner: Natural Soap or Neutral pH detergent
Finish: Polished - liquid Paste wax ; others:
none
Notes: Polished marble is ideal for vertical
application but requires a high level of maintenance when used
as flooring especially in high traffic situations.
Non-reflective finishes perform well as flooring with minimal
maintenance once treated with recommended sealers. Kitchen use
should be carefully evaluated due to oil absorption.
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Limestone
Composition:
Calcite, Calcium Carbonate
Hardness : Soft
Absorption : Oil, Water
Limitations : Absorbs oils and other liquids,
easily scratched, acid sensitive, polished-interior use only
Sealer : Penetrating type siloxane/fluoropolymer
Cleaner: Natural Soap or Neutral pH detergent
Finish: Polished - liquid Paste wax ; others:
none
Notes: Most true limestone types are porous and
absorbent. Some limestone is semi-metamorphic and will have
physical properties similar to metamorphic marble. If the
limestone is metamorphic it is "Marble". For our
purposes here, LIMESTONE is the chalky porous type typical of
most French and Spanish limestone. Non-reflective finishes are
practical as flooring but require sealing to minimize stains.
Dense, low absorbent varieties of limestone can be suitable in
shower areas but beware of using too soft a limestone in high
stress areas. Sealing is normally recommended for both
interior and exterior locations.
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Granite
Composition:
Quartz, Feldspar (varies)
Hardness : Hard
Absorption : Varies - Oil, Water
Limitations : Absorbs oils and other liquids,
brittle
Sealer : Sub-surface repellents - oil
repellent type recommended
Cleaner: Neutral pH detergent or pure soap
Finish: None Normally - Wax OK
Notes: Granite is typical for kitchen counter
use. Sealing is recommended for most stones. Granite is the
hardest of the polished stones commercially available and is
used in high stress situations. Polished granite usually is
more absorbent to liquids than many people suppose. Flamed
granite surfaces are very absorbent due to the stress
fractures in the stone caused by the flaming process and
should be sealed if it is desired to maintain the original
color and appearance of the stone over time.
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Slate
Composition:
Muscovite Chlorite (wide variation in composition)
Hardness : Soft - easily scratched
Absorption : Low - medium oil, water other
liquids
Limitations : Absorbs oils/ liquids, cleft
planes can spall
Sealer : Sub-surface repellents oil repellent
type recommended
Cleaner: Neutral pH detergent or pure soap
Finish: Acrylic OK - wax OK
Notes: Cleft slate is very durable in most
situations but quality varies. Slate is typically rustic in
appearance but some milled or smooth products are available in
some varieties. Wear is typically taken on the peaks or high
spots of the textured surface. Acrylics are used when a highly
reflective finish is desired. Excellent exterior paving stone.
Higher absorbency varieties may not be suitable for exterior
areas in freezing climates.
Slate characteristics vary with source. Domestic is typically
black, green or mottled (Pennsylvania) and is relatively
dense. Many imported slates are available today with wide
ranging physical characteristics and overall suitability.
Evaluate your stone for density, tensile strength, absorbency
and abrasion resistance. Make sure your slate characteristics
are compatible with the intended function. ÿÿ
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Considerations |
Surface
Textures
Heavy
Textures
Split face: Rough surface texture, ed rustic
Saw-cut: Rough saw finish, saw marks visible
Flamed: Damp stone spalled by acetylene torch
Sandblasted: Pitted, roughness depends upon
grit used
Smooth Textures
Honed: Smooth to the touch but not reflective
Polished: Mirror finish, (abrasive process)
Notes: Heavy Textures are most utilized for
rustic design needs and for slip resistance. Most will benefit
from treatment with repellents
Honed flooring surfaces do not show wear damage as
dramatically as polished surfaces do and therefore are more
economically maintained than polished surfaces.
Polished surfaces are ideally suited to low abrasive areas and
historically are best utilized as vertical surfaces. If
polished surfaces are used as flooring, restoration type
processes become a normal part of regular maintenance.
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Environment |
Kitchen
Areas : Kitchen areas are hostile environments. Stone
used in the kitchen should be as impervious as possible.
Hardness, loh absorption and easy wipe-ability are primary
physical characteristics necessary for long life and utility.
Bath Areas Stone inside showers and around
tub areas should be smooth and low absorbency. Polished
surfaces require special care in wet areas. Think of stone
installations in the bath area as you would a plumbing fixture
- you want a smooth, easily wiped surface that is easy to
sanitize and requires no special effort.
Hard water deposits can be very damaging to natural stone. If
you have hard water you should soften it. Chemical cleaners
should be carefully evaluated prior to using for compatibility
with the stone. Never use acidic type cleaners on marble or
limestone.
Exterior Areas Exterior stone will weather
sooner or later so expect some cosmetic changes over time.
Polished surfaces show cosmetic changes rapidly in most
exterior situations. Acid rain and pollution will attack
natural stones - some more readily than others. Carbonate
based stones are most sensitive, siliceous stone less
sensitive as a rule.
Maintenance Budget The most economical stone
surface to maintain is one that does not show cosmetic changes
during normal use. On stone floors this means a non-reflective
surface since foot traffic tends to abrade at a grit
approximating 120-220 grit. Polished stone surfaces re very
stable cosmetically if they are not subjected to abrasion and
chemical attack. Non-polished surfaces are more practical in
areas that are expected to be abraded, especially in high
traffic areas. Match the stone finish to the intended function
and abrasion level if you desire low maintenance costs.
There are situations where the design considerations will
outweigh the need for low maintenance costs and in these
situations the cost of restoration processes in addition to
normal cleaning need to be evaluated.
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Preventive
Maintenance |
Cleaning
Methods
Sweeping
: The old fashioned broom is still a valuable part of
everyday maintenance of any floor surface - stone included. It
is very important to remove soils from flooring surfaces
before they get ground into the floor. Soils are abrasive. The
more often soils are removed the longer the floor will retain
the original appearance. Use a broom with a bristle that
matches your surface. A soft broom or brush is recommended for
smooth surfaces. A medium-soft bristle is ideal for textured
surfaces.
Vacuum : A good vacuum cleaner works better
on textured surfaces than a broom and is very efficient. Use a
vacuum on any horizontal surface when large areas are involved
as it is faster than sweeping in most cases.
Damp Poming : A damp mop is capable of
picking up microscopic abrasive soils and potential staining
agents. Damp mopping is recommended for most smooth surfaces
on a regular basis. Best done after sweeping or vacuum.
Washing :It is necessary to wash a floor
regularly. The job conditions will dictate frequency. The most
frequent problems encountered with stone floors are related to
the floor simply not getting effectively washed often enough.
Rinsing : Rinsing is one of the most critical
steps in regular floor maintenance. Dirty mop water residue is
common and a cause for much complaint. A two bucket rinse
method is highly effective in keeping floors from graying out
due to soil residues.
Cleaning
Chemicals
Soaps : Natural soaps are low-tech,
inexpensive and user friendly. They are also capable of
providing a sealing and/or dressing function for stone floors.
Vegetable based soaps are best. Specialty soaps formulated for
use on stone are highly recommended and desirable on most
natural stone floors and other stone surfaces.
Detergents : These are synthetic
surface-active agents (surfactants) that are very good at
picking up soils and emulsifying grease and oil. They make
water "wetter" and more effective for cleaning
purposes. The detergent used for stone cleaning should be
carefully evaluated for compatibility with the stone.
Detergents are typically used with water and may determine the
pH of the cleaning solution. Detergents tend to leave the
stone very "raw" or absorbent and residues will make
water penetration into the stone more effective.
Acids : These are used for removing grout
haze, removing mineral dposits and for rust removal. Acidic
products attack lime and cement. Use caution with acids and
acidic pH products as they attack the polish on marnbles and
limestone. Phosphoric acid, citric acid and sulfamoc acid is
preferred to muriatic, sulphuric and hydrocloric acids in
almost all situations due to safety and control issues.
Abrasives : Abrasives are sometimes useful as
a cleaning agent but should be limited to non-polished
surfaces. Abrasives may be combined with detergents or soaps
for scouring a surface and removing thin layers from the
surface. There are many different types of materials used as
abrasives - soft abrasives may be composed of nut shells or
feldspars, hard abrasives can be silica quartz, carbide or
even diamond.
Bleaches : Bleaches are typically oxidizing
agents (generate oxygen) and are useful in stain removal.
Enzyme types are available which are non-hazardous.
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Preservations |
Sealing
Water
Repellents Silicone (synthetic oils) : Generic
synthetic oils which tend to leach from surfaces and migrate.
Of limited use due to the tendency of attracting dust and
limited life expectancy .There are many types but you can
generally rely upon the fact that you get what you pay for.
This type also darkens many types of stone surfaces.
Siliconates : Water based silicone derivative
useful for light colored, porous stone. Inexpensive.
This type should not be used on dark colored stone or
important surfaces. Any residues not absorbed will disfigure
surface with a salt-like precipitate. May be useful for some
limestone and concrete surfaces. Only water beads. Re-coating
is not possible due to the fact that it repels itself.
Siloxane : These are state of the art today
in long life and high vapor transmission. Moderate cost. Used
primarily for exterior stone surfaces including marble,
granite, limestone, slate and cement based building products
as well. Suitable for clay pavers and roofing tiles. Highly
recommended for most surfaces exposed to weather and/or high
humidity. Does not darken most surfaces. Solvent based is
normal. There are some new emulsions available which can
comply with VOC restrictions.
Stearates :This is the cheap water repellent
sold to consumers in chain stores and hardware stores for
wood, concrete, masonry etc.. Performance is poor and short
lived. Not recommended for most building stone.
Oil Repellents : These are proprietary
products which repel oil as well as water and other liquids.
There are a number of these specialized products designed for
use on stone surfaces. Most are fluoroplymer-based but there
are some other types (rather exotic)
Drying Oils : These are the original natural
polymers. They include Tung , Linseed and Soy. These oils
become solid as they dry and are of potential use for sealing
stone surfaces. They are organic and hence they are relatively
sensitive to aging and may (read: will) yellow with age but
are useful in some situations.
Waxes : Waxes may be natural or synthetic and
include Carnuaba, paraffin, montan, beeswax etc. They are
typically formulated into paste waxes or emulsions for sealing
purposes. Their effect is less than permanent and typically
they are re-applied on a regular basis.
Silicates : These are mineral glasses which
fill up pores and densify porous surfaces. Very useful for
restoration of stone which is under chemical attack or
exterior weathering as it can replace lost minerals (repair)
and provide protection from further degeneration. They are
specialized materials which require expertise to formulate and
apply for predictable results.
Finishing
Dressing
Waxes : This category is primarily paste
waxes composed of paraffin, beeswax, and some synthetics. They
can be very effective for maintaining a shine and prevention
of stains. Some professional products contain dyes or pigments
which can be useful in bringing out or maintaining the color
of red, black and green stones (primarily for furniture).
Carnuaba based waxes may be suitable for some low abrasive
surfaces and is used in specialty maintenance products.
Coatings : Coatings are usually acrylics,
urethanes, epoxies, varnishes, lacquers etc. and have limited
use on natural stone however there are some typical uses of
these film forming polymers. The most common coating is the
janitorial type floor finish that is applied to floors to
maintain a physical barrier which isolates the stone surface
from abrasion. These coatings are considered temporary or
sacrificial and are used primarily because the coating is
easier to restore when it gets damaged than the stone surface
would be without the coating. In general, film-forming coating
are avoided on natural stone if possible.
Soaps : Soap is potentially useful in a
number of categories because of the residue that soaps tend to
leave behind. The residue can be utilized as a sealer in some
situations or may be intentionally built up and used as a
natural paste wax or dressing. Soaps are very valuable for
maintaining stone surfaces and in most cases are 100%
reversible. Soap residues "dress" or nourish a
stone, preventing the stone from drying out and being overly
absorbent.
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Restoration |
Consolidation
Natural
stones age and weather with time. Binding of loose particulate
is a desirable process when it is necessary to arrest
degenerative processes. Limestone and sandstone are both
excellent candidates for binding processes which replace lost
minerals which hold the stone together.
There are many types of potential binding agents including
various polymers (acrylic, urethane, silicones, polyesters
etc.) as well as mineral based silicates available. Caution
must be exercised in the evaluation of a potential binding
agent as the physical compatibility of the binder with the
stone is critical.
Binding agents and processes are underutilized today primarily
due to lack of historical data regarding suitability and lack
of knowledgeable restoration specialists.
Filling
It is sometimes desirable to fill cavities in natural stone in
order to decrease maintenance costs, avoid mechanical trapping
of soils and contaminants or for design considerations.
Hardening : Some stones may be chemically
hardened in order to resist abrasion more effectively.
Limestone may be hardened by a number of chemical processes
including silica impregnators, silico-fluoride treatments, or
binding processes may give a hardening effect.
Strengthing : Stone strength is usually the
result of an increase in stone density brought about by
binding processes.
Grinding : Grinding is the historical method
of restoring a worn and weathered stone surface to it's
original cosmetic condition. It is also the pre-conditioning
stage for polishing with oxides. Silicon carbide and diamonds
are the most common abrasives used.
Polishing : This is usually a mechanical
abrasion process sometimes coupled with chemical action. A
typical polishing compound is composed of aluminum and/or tin
oxides and water. Oxalic acid is used as an additive for
polishing some marbles.
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