Photography and Editorial By: Dr. Christopher Cooper
The appearance of brick and stone masonry owes as much to the character of the mortar joints as to the brick and stones themselves. Unsuitable poorly executed repointing can affect not only the look but also the durability of masonry and is amongst the most frequent causes of damage to the character and fabric of a historic building.
The complete repointing of a building is rarely necessary. In most instances, only those parts that are most exposed to the weather or are affected by specific problems such as leaking rainwater down spouts or gutters are likely to be in need of attention. Sound historic mortar should be left undisturbed as it can be an important part of the character and significance of a building.
After reading this article, you may want to try your hand at repairing, restoring, and maintaining your own irreplaceable clay brick and stone. I have been teaching hands-on restoration masonry for over four decades and this in-person workshop on July 9th, 2022 will teach you the basics both in the cause and effect of deterioration. It will also instruct you on the step-by-step process to provide you with the confidence to tackle your own masonry repair and restoration project. Click on the link below to sign-up to this upcoming all hands-on workshop.
ONE: Inappropriate materials such as Portland cement!
More recent, 20th-century mortar has used Portland cement as a primary binding material. A straight Portland cement and sand mortar is extremely hard, resists the movement of water, shrinks upon setting, and undergoes relatively large thermal movements. When mixed with water, Portland cement forms a harsh, stiff paste that is quite unworkable, becoming hard very quickly. This type of mortar is the single biggest cause of severe damage to historic brick and should never be used in any quantity!
TWO: Water Management
The root cause of most deterioration is poor water management — leaking roofs or water splash from badly fitted gutters is a common cause, capillary action causing rising damp, or extreme weather exposure —should always be dealt with prior to beginning any repair work. Any vegetation or climbers in close proximity to the masonry must be removed because this can be the source of damp issues and damage.
One of the most common causes of spalling in heritage, solid walled buildings is the use of cement pointing, over soft lime mortar joints. Interstitial moisture is lost primarily through the mortar joints – the lungs of the wall – and when blocked with cement, this moisture then tries to escape through the brick faces, spalling and destroying them.
Water is absorbed by the porous surface of bricks, and in the winter months, expansion by freezing can cause bricks to crack or spall. Very soft lime mortar (devoid of any cement) will alleviate this problem, being highly porous, and it soaks up moisture, releasing it as conditions change.
Masonry sealants should never be used. They trap moisture and salts and exacerbate spalling. If spalling has already occurred, damaged bricks can be replaced, but the cause of the moisture should also be identified and dealt with appropriately.
FOUR: Pyramidal Cracking
There are many issues that plague heritage masonry not only from the natural age of the masonry units but also with such things as foundation issues and or a failed or rotten wood lintel or poorly constructed brick lintels.
In most situations such as the image above which is pyramidal cracking at the head and bed joints of the mortar is usually always owing to a shifting or a shrinkage of rotted wood lintels supporting the masonry load that is in vertical compression. Or in some cases with respects to an ill constructed jack arch or a segmental arch that distributes the vertical load above that is in compression, does not have enough bearing or angle on the springer brick to transmit loads to the left and right of an opening, therefore slipping… thus creating a pyramidal crack in the mortar. In most all these cases the best method of repair is to rebuild the jack or segmental arch wholesale and installing an appropriate steel lintel to support the brick work above.
The decision to repoint is most often related to some obvious sign of deterioration, such as disintegrating mortar, cracks in mortar joints, loose bricks or stones, damp walls or differential settlement of the building.
FIVE: Stress Cracking
Stress cracking is usually caused by a major structural issue. And should be addressed by a structural engineer prior to replacing any cracked or broken bricks.
Bricks will deteriorate through spalling as a result of moisture penetration, eventually resulting in the brick cracking. This can be a particular problem with softer, more absorbent bricks.
SIX: Media/Water Blasting
Any kind of blasting either sand or any kind of media or even power washing is not acceptable for use on handmade clay bricks… most handmade clay bricks only have a hardened exterior and are extremely soft on its interior… therefore, if this layer of hardness is eroded away by any type of media blasting or power washing the brick will be destroyed. In many cases when bricks are sand blasted the only remedy to stop further erosion is to either replace the brick wholesale or provide a hot lime wash to the brick to protect it from any further weathering. Power washing pushes massive amounts of moisture into the bricks and is done prior to a freeze the internal ice formation will spall the brick.
We have probably all seen it! That nasty white powdery coating that spoils the look of brick buildings. Efflorescence is a crystalline, salty deposit that occurs on the surfaces of bricks, concrete and other masonry products. Water from the grounds surface can often be the cause of efflorescence. For this water to carry the salts to the surface of the brick, there must be channels or fissures for the water to migrate.
The formation of these salt deposits is not an inexplicable phenomena, they are simply water soluble salts that come from different sources usually winter salting of sidewalks to ruin the looks of otherwise beautiful buildings.
EIGHT: Poor Execution!
Repointing can significantly affect not only the look but also the durability of masonry. If done badly or using the wrong materials, it can damage stone and brickwork, sometimes beyond repair. The images above sadly don’t need any description.
NINE: Hiring the right person for the job!
Repointing of historic stone and brick should only be done utilizing only an all lime-based mortar devoid of any Portland cement. Portland cement is too hard for historic stone and brick and should not be used in any amount!
Any mixes and recipes with any amounts of Portland cement are unacceptable to any house or building with handmade or soft clay bricks or sedimentary stone. Therefore, you will need to hire a mason that will use an all lime mortar, and settle for nothing less!
We are now taking applications for the Heritage Masonry Repair Programme commencing this fall if you are considering a career in Heritage Masonry – follow the link below.