Mix a joint mortar frost-proof and process

An appropriately mixed and processed joint mortar is frost-proof after complete setting and drying. Special care must be taken with water-permeable mortar. If water can collect in cavities caused by inadequate homogeneity of the mixture, it acts like a small detonator when frozen.

Water in the mortar develops explosive power

In outdoor areas, cement grout and in some cases lime cement mortar is used for grouting. Both mortar types are basically frost-resistant, provided that they have the correct mixing ratio, are properly processed, including a complete setting without disturbance counts.

The most important frost-preventing feature is the avoidance of water nests. When water penetrated in cavities freezes in the mortar, the ice develops by its specific expansion pressure on the mortar substance. With filled cavities, the pressure can escape only through the mortar itself and develops sufficient force to blow it. To prevent this effect, the following factors must be ensured for outdoor areas:

  • The mortar must give a very uniform and homogeneous mass when mixing itself, which has no air pockets
  • During setting and drying cracks in chamotte or paving grout must be topped up
  • For oven and outdoor fireplace, the fireclay mortar should be supported by proper insulation materials
  • If waterproof mortar is used, the drain in the joints must be ensured. Standing surface water, which freezes, develops explosive power similar to that in cavities
  • For permeable mortar, the base mortar or the gravel or sand bed must have sufficient drainage action to prevent backwater and thus standing water

Consider the structure from below

With regard to frost protection, we mostly take into account, for example, precipitation from the outside. The same "blasting effect" also occurs with water that reaches or penetrates from masonry or subsoil and soil to the mortar.

Joints must be compacted well to prevent cavitation between substrate and mortar. A multi-layered record with thorough repressions can minimize the risk of cavitation. On infiltrated surfaces such as gravel or sand, no waterproof mortar should be used. It forms a seal for the inevitable soil moisture, which can blow the mortar from below during frost.

Tips & Tricks

The choice of aggregates for your mortar will have special means of preventing frost damage. This reduces the risk additionally.

Product Image: touch1976 / Shutterstock

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