A Mortar for All Seasons

With winter well

on the way, anyone who has recently purchased an older property made of cob or

stone or both, may want to keep a close eye on the existing exterior render if

they suspect that it is not lime mortar, but instead has a cementious base that

may also have been sealed with a plastic paint.

 

The reasons for

this are straightforward- cement is a strong mortar and because it's

waterproof, actually creates a sealed surface which is rigid and non-

permeable, resulting in any moisture underneath getting trapped.  Cement is susceptible to frost and so in very

cold conditions will crack.  Not only

does it attract moisture it also retains it within the walls and other

materials around it such as lintels and windows.

 

Once frosted,

cement render will often fall off in clumps whilst inside, there will probably be

patches of damp appearing on walls and condensation problems, especially in

bathrooms and kitchens, as cement is not able to regulate the moisture content.

 

Lime mortar render

on the other hand is permeable which means that vapour can pass through it at

all times, providing a much healthier option. It's weatherproof, not

waterproof, meaning that your building is protected without sealing it. Lime

mortar does not attract moisture so it's not a wet material and therefore not

susceptible to frost; nor does it require the foundations to be below the frost

line.

 

Soft and

flexible, lime mortar allows stone or brick to move without cracking. As the

seasons changes so the mortar will flex without causing instability to the

structure, and unlike cement, there is no need to provide expansion joints.  Any small cracks that appear tend to do so in

a much reduced number of tiny micro cracks. Subsequent movement of rainwater

through the surface of the mortar joints dissolves the free lime which then

gets deposited in the micro cracks as the water evaporates. The lime

consequently reacts with the carbon dioxide in the air and is converted to

calcium carbonate and in a short period of time the cracks are healed- this is

known as autogenous healing. Whatever the weather, lime mortar is a mortar for

all season.

 

Heritage Cob and Lime

are manufacturers and suppliers of lime mortars and traditional building

materials. Based in North Devon they export across the UK. The company can be

contacted on 01237 477431 or through the website: www.heritagecobandlime.com