Hello
I've read through a lot of information on forums about dry mortar now and I want to see if I've understood it correctly.
1. Plaster and mortar come in different strengths with A being the hardest, then it goes down to B, C, and so on. Some retailers may label them as I, II, and III. There are pure lime mortars that are the weakest.
2. A harder mortar withstands weather better since it contains more cement but is not as flexible as, for instance, a C mortar or hydraulic lime mortar. Therefore, with temperature changes or movement in the building and foundation, an A mortar is more prone to cracking.
3. When plastering a completely new wall, you should start with red primer, which is as strong as an A mortar. But when renovating an old wall, the new plaster must be weaker than or the same as what is already on it.
4. If you have many house sides in the shade in a humid environment and need to rerender, make sure to get "hydraulic" lime mortar as it cures even in water.
5. At hardware stores, you often see Masonry/Plastering Mortar B and Plastering/Masonry Mortar B, but you can plaster with the masonry mortar and vice versa. However, the masonry mortar might have larger aggregate, so the plastering mortar becomes more flexible.
6. On some bags of mortar, it says Plastering Mortar C CS hand. This means it's a fairly weak plastering mortar meant to be applied by hand and probably has small aggregate.
7. If you are plastering a lightweight concrete block wall (Leca), you should first lightly water it, then apply a base mortar such as red primer to achieve an evenly absorbing wall before applying the next layer. You could use pure cement as the first layer here, but red primer is better at releasing moisture from the inside and is easier to work with. Then you put up a fiberglass mat or mesh directly against the priming mortar with stainless fasteners. After that, spray water again and apply the "stocking mortar" on the mesh, and this is the plaster that creates the thick layer, 5-15mm. Smooth it to an even wall after it has dried. Then use a C mortar or hydraulic lime mortar for the final plastering.
I've read through a lot of information on forums about dry mortar now and I want to see if I've understood it correctly.
1. Plaster and mortar come in different strengths with A being the hardest, then it goes down to B, C, and so on. Some retailers may label them as I, II, and III. There are pure lime mortars that are the weakest.
2. A harder mortar withstands weather better since it contains more cement but is not as flexible as, for instance, a C mortar or hydraulic lime mortar. Therefore, with temperature changes or movement in the building and foundation, an A mortar is more prone to cracking.
3. When plastering a completely new wall, you should start with red primer, which is as strong as an A mortar. But when renovating an old wall, the new plaster must be weaker than or the same as what is already on it.
4. If you have many house sides in the shade in a humid environment and need to rerender, make sure to get "hydraulic" lime mortar as it cures even in water.
5. At hardware stores, you often see Masonry/Plastering Mortar B and Plastering/Masonry Mortar B, but you can plaster with the masonry mortar and vice versa. However, the masonry mortar might have larger aggregate, so the plastering mortar becomes more flexible.
6. On some bags of mortar, it says Plastering Mortar C CS hand. This means it's a fairly weak plastering mortar meant to be applied by hand and probably has small aggregate.
7. If you are plastering a lightweight concrete block wall (Leca), you should first lightly water it, then apply a base mortar such as red primer to achieve an evenly absorbing wall before applying the next layer. You could use pure cement as the first layer here, but red primer is better at releasing moisture from the inside and is easier to work with. Then you put up a fiberglass mat or mesh directly against the priming mortar with stainless fasteners. After that, spray water again and apply the "stocking mortar" on the mesh, and this is the plaster that creates the thick layer, 5-15mm. Smooth it to an even wall after it has dried. Then use a C mortar or hydraulic lime mortar for the final plastering.
