Why does the stone return to alkali?

Reasons for stone returning to alkali:

The crystals of natural stones are rough, and there are many capillaries invisible to the naked eye. The porosity of granite is 0.5 ~ 1.5%, and that of marble is 0.5 ~ 2.0%. Its impermeability is not as good as ordinary cement mortar. The water absorption of granite is 0.2 ~ 1.7%, and water can still be conducted to the other side through the capillary immersion surface in the stone. This characteristic of natural stone and the existence of capillary holes provide a channel for the infiltration and precipitation of water, alkali, salt and other substances in cementitious materials and the formation of pan-alkali.

Bonding materials produce substances containing alkali, salt and other components. The main reason is the precipitation of calcium hydroxide in bonding mortar, followed by excessive mixing water, which invades the plate along the pores of the stone. The more mixing water, the more calcium hydroxide moves to the surface of mortar. After the water evaporates, calcium hydroxide will accumulate in the plate, forming a "white flower" phenomenon. The substances containing alkali, salt and other components produced by bonding materials are the direct material sources that penetrate into the pores of stone materials to produce pan-alkali.

Permeation of water. External wall joints are marked with cement fine sand mortar, which has poor waterproof effect; Groundwater (or moisture) invades the slate along the wall or mortar layer; When installing, too much water is sprayed on the stone, so that water invades the stone board, and salt substances such as calcium hydroxide are dissolved into the pores of the stone, forming pan-alkali.