The problems in cleaning stone and other porous surfaces are numerous notwithstanding the very nature of the stone specie and the type and extent of its damage. The general nature and source of dirt on the stone must be determined in order to remove it in the most effective, yet least harmful, manner. Types of ”dirt” include soot, smoke, leached salts, rust and organic stains, products of chemical attack from air pollution, micro-organisms and various applied coatings of paint, wax, etc. Stubborn dirt can be treated in a variety of ways including chemical cleaners and abrasives. Each method has its advantages and drawbacks. The safest of all stone cleaning methods is poulticing.
All stone cleaning procedures generally attempt to maximize cleaning power while minimizing chemical and physical attack that can result in further stone degradation. The use of inert natural clay poultices, or mud packs, is recognized as one of the safest methods for removing dirt deposits without affecting the stone’s integrity or surface detail. Poultices act to draw out hidden dirt, salts and microbes and is the least harmful of all techniques.
Laponite RD is a highly-purified, synthetic colloidal clay that imparts viscosity and suspension properties to various types of formulations. It's most often used as a very effective poulticing material for stone, ceramics, even paintings. It forms highly thixotropic, heat stable, clear and colorless gels when dispersed in water at a 2% solids levels. Laponite RD is free of crystalline silica and low in transition metals and other impurities.
Laponite RD is a free flowing white powder that when added to water with moderate agitation, will achieve optimum dispersion within thirty minutes. A 2% suspension of Laponite RD yields a pH level of approximately 9.8.