Types of mortars (wg DIN)
The following types of mortars are distinguished:
| Type of mortar (the ground) | Application | Minimum compressive strength |
| Pla and Plb Air-hardening lime mortar and water-hardening lime mortar | only for low mechanical loads | no requirements |
| Pic Hydraulic lime mortar | for normal loads | 1,0 N/mm2 |
| Pila High-hydraulic mortar Pllb Lime-cement mortar | for higher loads; plaster in wet and damp rooms | 2,5 N/mm2 |
The PN standard applies in Poland: Types of plaster bases. According to her, the substrate is divided according to the type of mortar on: W – limestone, C – cement, CW – cement-lime, CG1 – cement-clay, G – plaster, GW – gypsum-lime.
| Type of mortar (the ground) | Application | Minimum compressive strength |
| Pllla Cement mortar with calcium hydroxide
Plllb Cement mortar |
for heavy loads; plaster in wet and damp rooms | 10,0 N/mm2 |
| PIVa Gypsum mortar
PIVb Gypsum-sand mortar PIVc Gypsum-lime mortar |
for normal loads | 2,0 N/mm2 |
| PIVd Lime-gypsum mortar | only for light loads | 2,0 N/mm2 |
| PVa Anhydrite mortar
PVb Anhydrite-lime mortar |
for normal loads | no requirements |
How can you determine the type of mortar, which the hardened plaster was made of? First, but the inaccurate information is the color shade and the hardness of the plaster. The type of mortar can be determined much more precisely, when you rub a plaster sample in a mortar and sieve through a mesh screen 50 μm. Only the binder passes through this screen. By comparing the shade of the hue, the type of binder can be specified: the binding lime in the air is almost white, hydraulic lime – beige-gray and cement – Gray. A more accurate diagnosis requires laboratory tests.
Plasters must adhere evenly and firmly to their substrate. Within the plaster layer, the mortar should have a homogeneous structure and adequate strength. When applying thin coatings or wallpapers on plaster, the minimum strength of the mortar is required 1,0 N/mm2. Moreover, the plasters should be dry and evenly absorbent. They should also not have other disadvantages, like efflorescence, features, scale, contamination and fungus.
By capillary moisture is meant the appearance of water being pulled up by the capillaries (capillaries). Capillary moisture can cause the following damage:
1) plaster may crack or fall off;
2) salts can dissolve, coming out in the form of efflorescence to the surface;
3) plaster moisture reduces thermal insulation;
4) Winter, cracks may form in the plaster due to freezing of the water saturating the plaster;
5) moisture favors the growth of fungi, lichens and mosses.
Scale is an accumulation of binder on the surface, formed at that time, when the plaster is damp for too long. You can recognize her, wetting the surface after scratching; then the scratch spot turns darker due to stronger soaking. The scale must be removed mechanically. It can also be done with fluoride diluted in proportion 1:1, then you should place, from which the scale has been removed, gently wash off with water. Scale should be removed, because as a result of internal stresses, it flakes off the substrate after some time and causes the plaster patches to fall off.