Summer guidance for protecting Lime work
Protection must be given against extremes of rainfall, drying winds, direct sunlight and frost.
Protection should be considered for all mortar work in the early stages after placing, the degree of protection and the time will depend on ambient conditions.
- In wet conditions plastic sheeting should be used on the scaffolding, but can also be draped over the work. Special attention should be given to the top of the masonry wall to stop water entering through the vertical joints. Protection should remain in place until the surface of the mortar has achieved a set. Ensure any run off water from upper levels is well clear of any new work.
The worst combination of ambient conditions is heavy rain followed by clear skies and a frost. Saturated walls with under strength mortars will suffer frost damage much more easily than walls protected from the rain.
Damp conditions coupled with low temperatures will increase the setting time. To reduce these influences ensure the masonry units are not overly wet when laid.
- In drying winds (but in cold conditions) dry hessian and a plastic sheet or bubble-wrap should be draped over the completed area to control evaporation and cooling of the wall
- High temperatures, warm drying winds and direct sunlight care should be taken for work to covered as soon as possible with damp hessian to maintain moisture and then with additional cover to prevent hessian drying out. For best results the moist conditions should be maintained, whilst also allowing air movement over the mortar, for as long as is practicable
- Winter conditions will have the greatest effect on the setting of hydraulic mortars
Work should not be carried out if the temperature is below 5°C
When temperatures during first few days might fall to 5°C, or lower are forecast, protection is advisable as this will encourage the mortar to continue setting by keeping residual heat in. To achieve this use damp hessian to preserve the moisture and cover with a protective plastic sheet (or use bubble wrap), hung within 100mm of the surface.
5. Rate of set of hydraulic lime is more dependant on temperature than cement mortars. While mortars laid in the summer months may achieve frost resistance in a month, work done in cooler times of the year will indoubtedly take longer. As a result protection will be required for longer for upto 90days, perhaps for the remainder of the winter. During daylight hours, if warming winter sun is available, covers should be lifted to allow heat to be absorbed and then replaced in the late afternoon. Even under these conditions it is important to maintain air circulation between the covers and the masonry.