Correct Heritage Restoration Practices: The Dangers of Cement and Hydraulic Lime in Heritage Wall Repointing

25 Nov

Modern extension to a heritage home before restoration works. — *Heritage home facade showing deterioration - before render removal and brick and limestone restoration work.*

*Heritage home facade - after render removal and brick and limestone restoration by Regal Heritage Restoration.*

Should I use cement when restoring a heritage wall?

Heritage walls are not only beautiful, but they also offer a window into our history and traditional construction methods. Unfortunately, due to a lack of proper education, many heritage walls are "restored" improperly with cements, hydraulic lime, and adhesive additives, causing significant damage to our heritage homes and buildings.

Some examples of improper restoration and cement use include:

Rendering heritage brick and limestone walls with cement-based mortars
Repointing heritage walls with high cement content
Laying cement slabs up to heritage walls

Complications of using cement in heritage mortar

Using cement in heritage restoration can lead to several issues:

Rising damp: Cement traps moisture in the walls, preventing natural breathability.
Cracking: Cement is rigid and prone to cracking over time.
Fretting and deterioration of brickwork: Cement causes the bricks to deteriorate faster.
Fretting and deterioration of limestone blocks and rubble walls: Similar damage occurs to limestone structures.
Salt attack: Cement can exacerbate salt damage, accelerating decay.

Will removing cement render from a heritage wall help cure rising damp?

Yes, removing cement renders allows the walls to breathe. Over time, accumulated moisture can escape, which helps to alleviate rising damp. Removal of cement render can also expose the original beauty of the wall, revealing old brickwork, limestone blocks, rubble walls, and tuckpointed brickwork.

Should I remove cement mortar pointing ?

Yes, if the mortar is cement-based on a heritage brick or limestone wall. Removing improper cement mortars helps reduce fretting and the decaying of brick or stone faces, as well as the risk of future deterioration.

Removing cement repointing also helps to reduce the risk of:

Cracking
Rising damp
Salt attack
Unnatural-looking finishes

Should I use yellow sand when repointing heritage limestone?

No. When these buildings were constructed from the mid-1800s to early 1900s, yellow sand wasn’t available. Using yellow sand for restoration doesn’t provide the correct aesthetic for heritage walls.

What Sand Should I Use for Heritage Restoration?

Some good options for sand in heritage mortars include:

Lime sands: These can be graded in different sizes for the right texture.
Washed white sand: Free from salts.
Spearwood red: This sand has a pink/orange tone.

If you want a yellow-colored heritage mortar, sandstone, yellow ochres, and oxides can be added. Small amounts of yellow sand can also be mixed with white sand to offset the glare of stark white mortars.

What should I use instead of cement in a heritage wall?

Lime putty is the best product for making heritage mortars. It allows walls to breathe and gives an authentic, historical finish. Unlike cement, lime mortars improve with age through a fermentation process, which makes them more durable over time.

Should mortar be softer than brick?

Yes. Mortar should be softer than the brick, block, or rubble in a heritage wall. This prevents deterioration or fretting of the brick. It also reduces cracking and the need for future brick and stone replacement. In heritage restoration, we often use the term "sacrificial mortar," meaning that if either the brick or mortar deteriorates, the mortar is easier to replace than the brick or limestone.

At Regal Heritage Restoration, we believe in finding balance. Our goal is to create mortars that are softer than the brick or limestone, yet durable enough to reduce the need for constant maintenance.

Heritage restoration services in Perth, WA

If you’re interested in restoring your heritage home or building in Perth, Regal Heritage Restoration specializes in all aspects of masonry restoration, including: