Problems caused by using cement based mortar
Lime is more flexible than gypsum or cement, so is less likely to crack when plastered on walls or used for mortars or repointing.
Until the beginning of the last century most buildings were constructed with lime. Many of those now remaining have been repaired in recent years using portland cement based mortars and renders often with the following consequences:
- All buildings move, especially those pre-1900 which had less solid foundations. Cement mortars and renders are rigid and crack under stress. Often cement is stronger than the masonry – transferring fractures into surrounding brick or stonework.
- Cement due to its high density and crystal structure is ‘non porous’. Cement renders will crack eventually allowing water into the wall with little ability for the water to evaporate. In the case of cement mortars the evaporation can only take place through the masonry. This may result in increased spoiling of soft stone and brickwork leaving the mortar standing proud like a shelf, to collect more water, increasing the masonry’s deterioration. In addition walls will get damp resulting in internal mould and unhealthy living conditions.
- Chemical action between brick or stonework and cement can take place causing unsightly salt staining and in the case of some sandstone very rapid spoiling.
Thanks for the Lime Mortar, Lime Putty and colour Pigments you supplied this summer. It was a learning curve rendering the new extension and garden retaining walls (should have gone on one of your courses first!), however the advice provided by yourself onsite and colleagues over the phone ensured we got the job done. The rendering and Terracotta lime wash look really good and have provided that Mediterranean look I wanted, a really nice finishing touch to the extension. Excellent service and would fully recommend!
Mr. I Bell
Hot Lime Mortar Addresses these Issues
To some extent modern methods of construction have reduced, but not entirely eliminated these problems. With modern and older buildings therefore there are good reasons for using lime mortars, since:
- Walls breath better and moisture can evaporate.
- Mortars and renders do not set too hard.
- Thermal movement can be accommodated without damage.
- Expansion joints can often be avoided.
- Insulation is improved and cold bridging reduced.
- No risk of salt staining.
- Alterations can be effected easily and masonry re-used.
- Masonry life is increased.
One other reason for using limes relates to their environmental benefits. Because they are easy to remove, lime mortars allow recycling of valuable masonry units such as bricks, which have high embodied energy.
Advantages of Hot Mix Lime Mortar
There are many advantages to using Hot Lime Mortar including:
- High workability
- Increased productivity
- Fuller & compressed joints
- Can lay wet stones
- Cleaner work – no runs down the face of the work
- Able to build higher without squeeze
- Joint surfaces can be finished the same day
- Eliminates much of “touching up” afterwards
- Replicates original masonry