General Exterior Facade Chemical Cleaning Specifications
Marble & Limestone Cleaning
Always follow the manufacturer's recommendations and conduct small patch tests prior to commencing a cleaning operation. Limestone and marble are calcareous (calcium carbonate) stones and are very sensitive to chemicals (especially alkalines). Chemical cleaning specifications should ensure that any products used have been formulated for limestone and marble cleaning and that at the completion of the cleaning process, the stone is rinsed properly and left free of any residual alkalinity or acidity.|
Limestone and marble can be prerinsed using high pressure water (1500 PSI at 5 GPM) (19 Litres/Min. at 103 BAR). If the stone is blackened it may be necessary to preclean with an alkaline product. Starting from the bottom of the building, the product can be applied by brush, spray or roller going from natural break to natural break. After a 30 minute dwell time the alkaline phase can be rinsed using 1500 PSI at 5 GPM. It is recommended that a mild acidic cleaner be applied after the alkaline cleaner has been thoroughly rinsed. The acidic cleaner and subsequent rinsing will remove any residual inorganic contaminants and ensure that any remaining alkalinity is neutralized.
Under certain conditions, such as extreme friability of the stone, the rinsing pressure can be reduced.
If the limestone is lightly soiled, the alkaline precleaning may be eliminated. The stone can be prerinsed instead with plain water and then cleaned using acidic cleaning procedures.
Although limestone and marble substrates are self cleaning stones, many areas of a building are never exposed to rainwater. Over a period of years an encrusted black substance, chemically identified as calcium sulfate (gypsum), will form under cornices and belt courses. Unfortunately, the few chemical cleaners that can attack these encrusted areas will also attack the surrounding calcium carbonate. The calcium sulfate can be solubilized however by a prolonged soaking of plain water.
Prior to commencing a soaking operation the building shall be inspected for areas where leaking could occur. All obvious areas that would allow water penetration should be caulked or repointed.
City or well water shall be tested to determine the mineral content and the pH. Cascading water with a high mineral content (hard water) may cause the stone to discolor. Filters are available that can remove minerals from the water (soften) prior to soaking.
Incoming water should also be treated so that the water that is applied to the building will have a neutral pH (pH 7). Excess acidity or alkalinity may adversely affect the minerals in the stone or the stone itself.
During the course of all water soaking operations, one workman of supervisory caliber shall personally view and inspect all interior areas of the building to guard against water penetration.
Troughs shall be erected to direct the cascading water away from the building foundation to prevent leakage into the basement areas.
The soaking manifolds and nozzles (all parts non-ferrous) shall be positioned to allow for directing water sprays equally over all calcium sulfate areas. Manifolds, hoses, etc., shall be securely fastened to the scaffolding.
The water soaking process shall in each instance commence at the topmost reaches of a particular segment of the structure. When soaking is completed the equipment shall be lowered in a straight line to the lowest point that requires treatment.
When certain stone elements are to be water soaked, equipment shall be arranged to reach all parts simultaneously; resetting equipment to reach other parts of the same stone element shall be avoided.
Soaking cycles shall be accomplished at six (6) hour intervals of soaking and repose. The soaking process shall be repeated until the treated surface is acceptable to the architect.
Under no circumstance shall water pressure be employed to dislodge carbon encrustation. All nozzles shall be set to provide "little more" than a heavy mist to all affected surfaces.
A light brushing of surfaces using tampico fiber brushes may be employed if found necessary to produce desired results.
The soaking shall continue until the calcium sulfate has been dissolved. The stone shall then be cleaned using the alkaline/acid method described previously.
Treatment of contaminants such as iron oxides (rust) copper stains, graffiti or the removal of sealants may require the use of compatible products or a second application of the base product. Exact procedures can be determined by reviewing the manufacturer's literature or by consulting with the manufacturer's representative.
The manufacturer has developed his cleaning systems to perform certain predetermined tasks. Any deviation from the prescribed methods and procedures may compromise the end results.