Winter & quality
Winter bricklaying — measures in frosty weather
Temperature requirements, tempered water, antifreeze and covering
Masonry must not freeze before the mortar has cured sufficiently. Below +5 °C, winter measures must therefore be taken: heated mixing water, shorter working time, frost-free covering and — only if the project allows it — antifreeze. The guide brings together the citable limit values from Mur & Tag and Teknologisk Institut.
Assess whether winter measures are needed
Winter measures are recommended when the temperature falls below +5 °C. Below that limit, the mortar cures too slowly and there is a risk of frost damage in the fresh masonry.
Limitbelow +5 °CEnsure +5 °C in the substrate and materials
The substrate and materials must be at a temperature of at least +5 °C for the mortar to cure quickly enough. Cold bricks and a cold foundation draw the heat out of the mortar — keep the materials warm and dry until use.
Min. temperature+5 °CHeat the mixing water — but not too much
The mixing water can be heated to raise the mortar temperature, but the water temperature must not exceed 80 °C. A higher temperature risks an abnormal chemical reaction in the binder.
Max. water temperature80 °CAllow for a shorter usable life
In cold weather the mortar's working life is short: approx. 1 hour at −5 °C with 20 °C warm mortar in an uninsulated tub. So mix smaller batches at a time, and keep the mortar warm until it is used.
Pot lifeapprox. 1 hour at −5 °CKeep the masonry frost-free until it has cured
The temperature of the new masonry must be kept above freezing until the bricks have drawn so much water out of the mortar that the water content is down to no more than 7–8 %. Only then is the risk of frost damage over.
Water contentmax. 7–8 %Only use antifreeze if the project allows it
Antifreeze (denatured spirit or an ethanol/isopropanol mixture, max. 40 % isopropanol) can be used for lime and lime-cement mortar at no less than 1 and no more than 4 litres per 100 litres of mortar. However, it may only be used if it is specifically permitted in the project documents — and must never be added to dry mortar.
Dosing1–4 L per 100 L mortarAntifreeze is not a free shortcut: it may only be used when the project documents allow it, and never in dry mortar.
Cover the masonry watertight
Cover fresh masonry with winter mats and tarpaulin in frosty weather. The covering must be watertight and securely fixed so that rain and meltwater cannot get in and freeze in the structure.
Postpone the pointing — or wait for better weather
Postpone subsequent pointing until there is no longer any risk of frost. If the masonry cannot be kept frost-free despite the measures, better weather should be awaited rather than continuing to lay.
Source
Based on Mur & Tag (mur-tag.dk/udfoerelse/opmuring/vinterforanstaltninger/vejledning) and Teknologisk Institut «Vintermuring» (Jens Østergaard).