1. Industry and traffic are major air
   polluters. The burning of oil derivitives
   and coal produces sulphur dioxides  
   which turn into sulphuric acid. Nitrogen oxide is produced by the internal combustion engine and becomes nitric acid. Natural stone is composed mainly
   of lime, which is sensitive to acid rain.
   
   
2. A crust can form on the surface of stone and brick composed of soot and a dusty amalgam of previously-described pollutants. When this happens, a layer
   of calcium sulfate (patina) is deposited which is hardly permeable at all to water.

   The moisture within the stone accu-mulates beneath the patina layer. Sait crystallization leads to volume expansion, and the stone begins to crumble.

   For this reason it is extremely important to prevent water penetration without affecting the vapour diffusion properties
   of the stone.
   

3. Micro-organisms proliferate when brick
   and stone are exposed to damp
   conditions. The clearest sign of these is the formation of moss and algae: they give rise to continuous maintenance and its consequent cost. Moss and algae also hold back moisture, which increases the risk of frost damage.
   
   
4. Water that penetrates through capillary action or cracks can cause an expansion
   of volume that can reach as high as
   10%, which in turn can cause brick or stone to crumble. Certain mortars, such
   as those used as filler between bricks
   and stones, can begin to erode or cause displacement with the repetition of freeze/thaw cycles.

Graftex® protects against:

1)- Gases, preventing penetration of carbon dioxide and sulphur dioxide.

2)- Rain, preventing infiltration of acidic or sulphurous water.