Materials

Stone Types | Considerations | Environment | Preventive Maintenance| Preservation | Restoration
 

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.

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.

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.

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.

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.

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.

Environment

Kitchen Areas : Kitchen areas are hostile environments. Stone used in the kitchen should be as impervious as possible. Hardness, low 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.

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 Moping : 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 deposits and for rust removal. Acidic products attack lime and cement. Use caution with acids and acidic pH products as they attack the polish on marbles 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.

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.

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.