How To Protect Natural Stones?
In ancient as well as modern architectural structures, stones have been a widely used building material. Their abundance, strength, and durability have altered the history of mankind. With increasing hybridization and innovation in construction materials, the use of stone in construction has fallen down over the last hundred years, but it remains an aristocrat of building materials.
The preservation of stone is necessary to prevent its decay. Different types of stones demand different treatments and preservatives. However, with the help of preservatives, the rate of decay can only be slowed but can’t be entirely prevented. Hence, all the preservatives are proved temporary, and these are yet successful in the establishment of appearance and strength of stone.
Temporary Methods To Protect Stones:
The temporary treatment is to dry the stone with the help of a blowlamp and then provide a coating of Paraffin/Linseed oil/light paint. However, prior to the application of linseed oil, it should be boiled and then applied in three coats over the stone, and thereafter, a coat of dilute ammonia in warm water is applied.
1. Washing of Stone with Szerlmy’s Liquid
The best way is to wash the stones with a thin solution of silicate of soda or potash. On drying, apply a solution of CaCl2. Both of the solutions collectively called Szerelmy’s liquid combine to form silicate of lime, which seals the pores in a stone. Salts formed are washed away, and an insoluble film is acquired on a stone that safeguards it.
2. Water Repellant Treatment for Freeze-Thaw Damage
Sometimes the continuous repetition of Freeze-Thaw cycles can damage porous stones. Water which enters into the pores of stone expands on freezing and causes spalling. It should be noted that stones of low porosity should not be used.
If this is not possible, then the stone should be treated with water repellants. ProSoCo H40 and H100 are water repellant treatments and increase the strength of stones by depositing silica into pore spaces.
3. Stone Cleaning
After installation, stones must be cleaned. The most common stone is Muritaric Acid diluted with water. This solution removes stains from the stones. It should be noted that this cleaner is not valid for limestones and marbles because acid discolors the stone. ProSoCo’s Safety Klean is safer to use on limestone and marbles.
4. Surface Treatment with Chemicals
Many times, lead paint is also used as a preservative, but this method became orthodox due to its deteriorating the natural color of the stone. Painting stones with coal tar is also very helpful in the preservation of stones, but it also spoils the appearance and beauty of the stone.
So these chemicals should be avoided because a stone preservative is always intended to prolong the life of a stone without changing the natural appearance or architectural value of the stone.
i) Color Enhancers
Most of the time, the natural color of the stone is not according to the taste of clients and Architects. So, color enhancers are used to deepen the color of stones. These enhancers also provide water and stain repellency. Various types of color enhancers are available in the market.
ii) Preservation Of Industrial Building With Baryta
Majorly, in industrial towns, stones are preserved with the solution of Ba(OH)2 – barium hydrate, commonly known as Baryta. Acid contains Sulphur dioxide, which reacts with Calcium contents of stones to form Calcium Sulphate. Dust and soot present in environment stick to the calcium sulfate and form a hard skin.
In due time, Calcium Sulphate so formed flakes off and exposes the fresh stone surface attack. This is popularly known as the Sulphate attack.
Baryta reacts with Calcium Sulphate, which is deposited on the surface of stones and forms insoluble barium sulfate and calcium hydroxide. The calcium hydroxide absorbs CO2 from the air to form Calcium Carbonate.
Ba (OH)2 + CaSO4 ———–^ BaSO4 + Ca(OH)2
Ca(OH)2 + CO2 —————^ CaCO3 + H2O (Calcium carbonate)
iii) Protection Against Salt Damage
Salt damage is common in porous stones that are exposed to salty water. On penetration of salty water, the salt crystallizes in the pore spaces and thus causes discoloration and spalling. For this, Prosco Salt Guard is used. This repels water, and hence it is applied on the face of the finished stone wall or surface of the floor. Salt damage can also occur with the moisture of the soil.