Cement is strong, durable and invaluable in modern construction. But strength alone does not make a material suitable for every building.
Across Britain, many traditional stone properties were constructed long before modern Portland cement became commonplace. Their walls were built using natural stone and comparatively soft lime mortar—materials that could absorb moisture, release it and accommodate the small movements that occur naturally over time.
When hard cement mortar or render is added to these older walls, it can fundamentally change how the building performs. The repair may initially look solid and reassuring, while deterioration develops slowly beneath or around it.
Understanding this difference can help property owners avoid short-term repairs that create far more expensive problems later.
Stone buildings were designed to manage moisture
Many traditional stone buildings, particularly those built before 1919, have thick solid walls rather than modern cavity walls.
These walls may contain two outer faces of stone with a rubble-filled core between them. Lime mortar binds the masonry together while allowing a degree of moisture movement through the wall and, importantly, through the mortar joints.
Traditional walls were not designed to be completely sealed. Rainwater, ground moisture and water vapour could enter the building fabric in small amounts, but the materials also allowed that moisture to evaporate when conditions improved.
The mortar joints played an important role in this process. Because lime mortar was generally softer and more porous than the stone, moisture could escape through the joints rather than being driven through the stone itself.
What changed when cement became widely available?
Portland cement became increasingly common during the 19th and 20th centuries. It set more quickly than traditional lime, offered predictable strength and suited the demands of modern construction.
As its use expanded, cement mortars and renders were also applied to older stone buildings. They were often seen as a stronger and more permanent alternative to the softer lime materials they replaced.
Unfortunately, traditional walls do not always benefit from being made harder or more waterproof.
Cement can be significantly harder, denser and less moisture-permeable than the original stone and lime mortar. Instead of working with the building’s natural movement and moisture cycle, it can restrict them.
The problem with hard cement pointing
Pointing is intended to protect the joints between stones. In a traditionally constructed wall, the pointing should usually be softer and more sacrificial than the stone around it.
This means the mortar takes the effects of weathering and can eventually be replaced, preserving the more valuable and often irreplaceable stone.
Hard cement pointing can reverse that relationship.
If moisture can no longer evaporate readily through the mortar joint, it may be pushed towards the exposed surface of the stone. The stone, rather than the mortar, then becomes the route through which the wall attempts to dry.
Over time, this can cause:
- Flaking or crumbling stone surfaces
- Erosion around the edges of individual stones
- Cracking beside hard cement joints
- Damp remaining within the wall for longer
- Salt deposits and staining
- Frost-related damage during cold weather
- Loosening and instability within the masonry
The cement joint may remain visually intact while the surrounding stone deteriorates. What appears to be the strongest part of the wall can therefore contribute to damage in the material it was supposed to protect.
How moisture damages stone
Stone may appear solid, but many types contain a network of tiny pores through which moisture can travel.
When moisture is trapped within porous stone, repeated wetting and drying can gradually weaken its surface. Water may also carry naturally occurring salts through the masonry. As the wall dries, these salts crystallise near or beneath the stone’s surface.
The pressure created by salt crystallisation can cause the surface to powder, blister or break away—a process sometimes called spalling.
Cold weather creates another risk. Water held within vulnerable stone can freeze and expand. Repeated freeze-and-thaw cycles can widen existing weaknesses and cause the outer face to detach.
Not every type of stone reacts in exactly the same way. Sandstone, limestone, rubble stone and other local materials have different characteristics. The condition of the wall, its exposure and the strength of the cement all affect how quickly problems develop.
The risks of cement render
Cement render can create similar problems on a larger scale.
When first applied, it may appear to provide a tough, weatherproof coating. However, traditional buildings naturally experience small amounts of movement. A rigid cement render may not be able to accommodate this movement, causing fine cracks to form.
Rainwater can enter through those cracks, particularly on exposed elevations. Because the render restricts evaporation, the moisture may then become trapped behind it.
The visible symptoms can include:
- Hollow or drummy areas where the render has lost its bond
- Cracking around windows, doors and changes in the wall
- Bulging or detached sections of render
- Damp patches appearing internally
- Mould, staining or peeling paint
- Decay of concealed timber lintels or structural timbers
- Deterioration of the stone behind the apparently sound surface
In some cases, the full extent of the damage only becomes visible when the cement render is eventually removed.
Why the damage happens gradually
One reason inappropriate cement repairs can remain in place for so long is that deterioration is often slow.
A newly cement-pointed or rendered wall may look neat and secure. Problems develop through repeated seasonal cycles of rain, drying, heat, cold and frost.
The progression may look something like this:
- Cement restricts evaporation through the joints or wall surface.
- Moisture remains within the wall for longer.
- Small cracks allow additional rainwater to enter.
- Moisture is redirected through the softer stone or towards the interior.
- Salts move and crystallise as the wall attempts to dry.
- Stone surfaces begin to powder, flake or break away.
- Cracks and failed surfaces allow even more water into the structure.
- Repairs become progressively more complex and costly.
The exact process varies between buildings, but the principle is consistent: a material intended to provide protection can create conditions that accelerate deterioration elsewhere.
Warning signs to look for
Property owners should consider seeking specialist advice if they notice:
- Very hard, smooth or raised pointing around older stonework
- Crumbling stone beside mortar joints that remain intact
- Stone faces breaking away in thin layers
- Cracks running along the edges of cement repairs
- White, powdery salt deposits
- Dark damp patches that take a long time to dry
- Cement render that sounds hollow when lightly tapped
- Bulging, cracked or detached render
- Repeated failure of internal paint or plaster
- Persistent damp despite previous waterproofing treatments
These symptoms do not automatically prove that cement is the only cause. Defective roofs, gutters, downpipes, drainage, plumbing, external ground levels and poor ventilation must also be investigated.
A building should be assessed as a whole before repairs are specified.
Should cement always be removed?
Not necessarily.
Removing inappropriate cement can help a traditional wall dry and restore its intended performance, but removal itself carries risks. Hard cement may be strongly bonded to the surface of softer stone. Aggressive tools or rushed workmanship can pull away the stone face, damage edges or widen the joints.
In some cases, selective removal may be safer than stripping everything at once. Trial areas can help establish how firmly the cement is attached and how vulnerable the underlying masonry may be.
Before work begins, it is important to consider:
- The type and condition of the stone
- The depth and hardness of the cement
- Whether the cement is pointing, render or a previous structural repair
- The condition of the original mortar behind it
- The source of any moisture
- The exposure and location of the wall
- Whether the property is listed or subject to conservation controls
- How the wall will be protected and allowed to dry after removal
Listed building consent may be required where work affects historic fabric or the character of a listed property. Owners should check requirements before starting.
Repairing the wall properly
Where removal is appropriate, the work should be approached carefully and in manageable sections.
Cement pointing is normally cut out by hand or with carefully controlled tools to avoid damaging the surrounding stone. The joints must be cleared to a suitable depth, but they should not be unnecessarily widened or made mechanically uniform.
Once prepared, the wall can be repointed using a compatible lime mortar selected for the particular stone, location and degree of exposure.
If cement render is removed, the underlying wall may need time to dry before repairs or new finishes are applied. Damaged joints, loose stones and areas of decay must be addressed before a suitable lime render or other breathable finish is introduced.
As with all lime work, correct curing is essential. The new material may need protection from direct sun, strong wind, heavy rain and frost while it develops strength.
This process takes longer than applying another hard cement coating, but it addresses the compatibility of the whole wall rather than simply covering the visible symptoms.
Investing before the damage becomes severe
Replacing inappropriate cement work can be a significant undertaking, particularly if access, scaffolding or extensive stone repairs are required.
However, leaving the problem until large areas of stone have deteriorated can be considerably more expensive. Mortar is replaceable; historic stone often is not.
Early assessment is particularly worthwhile when:
- Stone is beginning to crumble beside cement joints
- A property is being renovated or purchased
- Scaffolding is already being erected for roofing or external work
- Damp has persisted despite repeated treatments
- Cement render is cracked, hollow or failing
- Repointing is planned for a large area
- The building is listed or has important historic character
The objective is not to make an old building behave like a new one. It is to understand how it was constructed and use materials that support its original performance.
Matching the repair to the building
Traditional stone buildings have survived for generations because their materials were able to work together. Replacing a soft, moisture-permeable component with a much harder and denser one can disturb that balance.
At McCall Construction, we understand that repairs to traditional stonework require more than simply applying the strongest available product. We assess the masonry, existing mortar, moisture patterns and likely causes of deterioration before recommending an appropriate solution.
Where unsuitable cement needs to be removed, the work must be carried out carefully to protect the stone beneath. Any replacement mortar or render should then be chosen to suit the building—not simply the speed of the job.
If your property has crumbling stone, hard cement pointing, cracked render or persistent damp, contact McCall Construction for an informed assessment. Acting before deterioration becomes severe can protect the building’s appearance, preserve its historic fabric and prevent a manageable repair from becoming a major restoration.
