Cornwall’s granite, slate, lime and cob cottages and townhouses are often deeply misunderstood, frequently by professionals such as surveyors and even more so by local tradespeople who have worked on them their entire lives.

So how has this situation come to be this way?

In the late Victorian era through to the present day there have been remarkable break throughs in construction design and technology. The financial yearning to build more quickly and to prolong the cadence cycles of property maintenance has seen us traverse through a period of using non-breathable materials that were supposedly meant to require little or no maintenance. We moved away from natural timbers and limes that not only allow, but support moisture movement within a building and were left with modern materials that trap moisture and in most cases, lead to the destruction of any historic building fabrics that they come into contact with.

Thankfully, there is a trend slowly emerging, where we in many aspects of our lives are seeing past the marketing schemes of big business and are seeking more common sense, holistic solutions to issues that have plagued our modern times. However, until these holistic methods become common practice, we need to understand the players in the game…

Local tradespeople: Many highly experienced, local tradespeople started their careers in the 60’s through to the millennium. It was through this time in construction history that these inappropriate materials were introduced as cutting edge technology and many tradespeople still hold those beliefs, despite the mounting evidence of their failures.

RICS (Royal Institute of Chartered Surveyors) Surveyors: as within any profession, there are many surveyors who are excellent at what they do. Some are deeply knowledgeable about heritage buildings and building pathology, with a true understanding of how older structures “live and breathe,” as well as the traditional materials and techniques required to conserve and protect historic fabric.

However, there are also surveyors who may recommend generic damp-proofing systems or chemical quick-fixes. Why does this happen? In many cases, it may be due to a limited understanding of traditional construction, combined with the need to minimise their own professional risk and to meet the cautious requirements of mortgage lenders.

Damp proofers: The industry is worth a total of 200 millions pounds a year in the UK, and there are those who will jump at the chance to relieve you of your hard earned cash, no matter how unethical the process. And sadly, a 200 million pound market knows how to promote itself, where as heritage conservation specialists are more prone to keeping knowledge and skills to themselves, which inevitably exacerbates the situation.

I’ll begin with perhaps the most controversial form of dampness found in homes: rising damp. It is controversial because a large proportion of heritage conservation professionals argue that it does not truly exist.

‘True rising damp’ is defined as the upward movement of liquid water through masonry via capillary action. Some claim it is an exceptionally rare phenomenon. However, independent surveys and scientific research indicate otherwise, showing that, under the right conditions, rising damp can and does occur.

Rising damp however, is by far, the single most falsely diagnosed form of damp by dodgy damp proofers and this is because it’s extremely profitable to ‘fix’ with the use of tanking systems / cavity drain membrane and chemical DPC’s.

And their evidence for this rising damp? The only instrument that they will have to qualify this diagnosis is a ‘damp meter’, which is woefully inadequate and inappropriate. In fact, the British Standards state that damp meters alone cannot give proof of rising damp – yet in your Home Buyers or Timber and Damp report you may well see images of said damp meter as the only evidence.

British standard- BS 6576: Code of practice for diagnosing rising damp in walls and buildings and installation of damp-proof courses. ‘Surface measurements cannot alone give proof of rising damp, so further evidence may, where permitted, be obtained by measurements taken within the depth of the wall. Chemical (carbide) or gravimetric methods can be used.’

Please note: that rising damp is a very emotionally charged topic within the construction industry, with tradespeople and specialists on both sides in total disagreement as to the possibility for water to move up though masonry from the ground. My opinion is that this is that capillary rise is easily evidenced by placing a brick in a shallow tray of water, the water moves up the brick, both internally and externally. In my other articles I describe the mechanics of capillary action via hydrogen bonds.

The causes of rising damp
My definition of rising damp (which may differ to other surveyors) is any form of moisture moving up from the ground into a building. This might be caused by:
– An escape of water from drain, plumbing, rainwater or heating
– Exterior ground levels too high
– Insufficient surface water drainage
– Rainwater downpipe discharging to the ground
– Cement render run to the ground
– Local water table too high (rare & not a building defect)

The symptoms of rising damp
– Wet patches or bands of salts appearing on internal walls from the floor to wall junction up to a hight of approximately 1500mm.
– Saturated timber joist ends where they are in contact with the ground or a solid wall
– Deformed / cupped timber flooring

How to evidence or assess rising damp
Assess:
– Drain camera survey
– Plumbing survey
– Thermographic imaging
Evidence:
– Carbide meter / gravimetric moisture testing of masonry
– Salt analysis

How to resolve rising damp
By addressing any of the potential building defects listed above
Following this, the application of lime plaster and mortars will resolve very low levels of rising dampness.

How not to resolve rising damp
– By only applying lime and not resolving the building defect
– By installing damp proofing systems that only temporarily hide / redirect the dampness else where.

You can read my article called How rising damp & condensation are misdiagnosed – moisture entrapment & damp meters here…

Penetrating damp is a form of dampness that occurs when water penetrates through the walls or roof of a building, leading to the appearance of damp patches or stains on the interior surfaces. Unlike rising damp, which typically affects the lower parts of walls due to groundwater rising through capillaries in the masonry, penetrating damp is caused by water infiltrating the building envelope from the outside or above.

Though unlike rising damp, dodgy damp proofers often diagnose the building defect correctly, but then suggest completely inappropriate ways of hiding the dampness… such as tanking systems, insulated plaster boards and stain blocker paints, rather than tackling the building defect at the source.

It is important to access walls at height to fully survey the potential for mortar or render failure. With pointing look for cracks or disintegrating mortar. For render look for cracks and tap the surface to see if it sounds hollow / blown.

The causes of penetrating damp
My definition of penetrating damp is any form of moisture moving inwards or downwards into a building. This might be caused by:
– The incorrect lime mortar being used
– Failed cement pointing, render or lead flashings
– Raised ground levels, with walls below ground
– Blocked gutters
– Leaking roofs

The symptoms of penetrating damp
– Wet patches or bands of salts appearing on internal walls at any height.

How to evidence or assess penetrating damp
Assess:
– Thermographic imaging
Evidence:
– Water (spray) testing combined with thermographic imaging
– Carbide meter / gravimetric moisture testing of masonry
– Salt analysis

How to resolve penetrating damp
By addressing any of the potential building defects listed above, removing cement and replacing with the correct lime mortar.

How not to resolve penetrating damp
– By only applying lime pointing / render and not resolving the building defect
– By installing damp proofing systems that only temporarily hide / redirect the dampness else where.

Chimney dampness can be loosely split into three categories, though they closely relate to one another.

1: Hygroscopic salts are water attracting in nature, they commonly present as either powder like salt deposits on masonry walls or damp patches on internal wall papered or painted surfaces. They are deposited with the masonry through the burning of fossil fuels and mobilised via moisture movement.

As they can only mobilise via moisture movement, therefore, there must be some form of building defect at the root cause, such as condensation within the flue or water ingress externally on the stack or crown.

2: Condensation within the flue is typically caused by a lack of ventilation or removal of a chimney. Due to a lack of an updraft (which occurs naturally) condensation forms within the flue, moves through the masonry due to capillary action, taking hygroscopic salts with it.

3: Chimney stack or crown failure can occur in multiple forms for many reasons.

– Lead flashings can become dislodged or lose their surrounding mortar.
– Chimney crowns can split and allow water penetration
– A chimney’s pointing or render can fail, often because an an inappropriate repair materials was used.

Chimney dampness and repair is a complicated issue, for more information please read the following articles:
> Dampness within chimneys and common defects
> Flue liners and condensation issues
> Hygroscopic salts – damp patches on chimney breasts
> Chimney repair and rebuild information

A chimney breast showing hygroscopic salt dampness

Moisture entrapment

Moisture entrapment can occur when water, either in liquid form or as vapour, moves through masonry by capillary action or vapour diffusion and then becomes “trapped” by non-breathable or hydrophilic (moisture-retaining) materials such as cement renders, gypsum plasters, tanking slurries, or plastic-based paints.

The microscopic capillaries within the masonry, which are essentially tiny cracks or air pockets in the material, can become saturated with moisture. Once filled, these pathways no longer allow the water to escape, leading to a build-up of moisture within the wall fabric.

This trapped moisture reduces thermal performance, cools the wall, and increases the likelihood of condensation and mould growth within the building.

A useful way to picture this is to imagine placing a towel (the masonry wall) inside a plastic bag (the cement render or plastic paint). The bag is full of tiny cuts or pores. If you then soak the bag with a hose (representing internal vapour pressure or driving rain), water is driven in and the towel becomes saturated. But how effective will the evaporation process be with the towel encased in plastic? The drying forces will be far weaker than the forces that made the towel wet in the first place, so the moisture remains trapped.

The causes of moisture entrapment
My definition of moisture entrapment is where walls and their coverings reach a point of saturation due to a lack of vapour permeability or capillary action.

The symptoms of moisture entrapment
– Wet patches or patches of salts appearing on internal walls
– Decorative spoiling such as paint peeling
– High moisture levels in structural & decorative timbers
– Mould growth

How to evidence moisture entrapment:
– Carbide meter / gravimetric moisture testing of masonry
– Samling to identify paint and plaster type

How to resolve moisture entrapment
Remove low-vapour permeable / hydrophilic materials such as plastic paints, cement and gypsum plaster.
Following this, the application of high vapour permeable materials will resolve very low levels of moisture entrapment.

How not to resolve moisture entrapment
– By only applying lime internally and not resolving any contributing building defects
– By installing damp proofing systems that only temporarily hide / redirect the dampness else where.

Interstitial Condensation

Interstitial condensation takes place within the fabric of a wall, floor, or roof rather than on the surface. It occurs when water vapour moving through the structure encounters a layer or zone that is colder than the dew point. At this point the vapour condenses into liquid water inside the material.

This problem is often linked to retrofits where non-breathable materials, insulation layers, or vapour barriers are present. When vapour cannot pass freely through the building fabric it may be forced to condense within hidden layers. A lack of effective ventilation allows vapour pressure to build inside the property, while inadequate heating leaves internal walls cold. The combination of high vapour pressure and cold surfaces increases the likelihood of condensation taking place within the structure.

In some cases interstitial condensation can also be triggered by saturation. When the pores of the material are already filled with liquid water, any additional vapour has nowhere to go and is forced to condense within the structure. This mechanism is very similar to moisture entrapment and the two effects often overlap in practice.

Over time this concealed moisture can build up and saturate insulation, timbers, or masonry. The consequences include reduced thermal performance, decay of structural elements, and the development of mould in areas that are not immediately visible. Because it occurs inside the structure, interstitial condensation can remain unnoticed until significant damage has taken place.

A useful way to understand this is to think of a cold drinks can on a warm day. Droplets form on the outside of the can because the air in contact with the surface has reached its dew point. With interstitial condensation the same principle applies, but instead of droplets forming on a visible surface they appear within the wall or roof, hidden from view.

The causes of interstitial condensation
My definition of interstitial condensation is where vapour moving through the building fabric condenses into liquid within the structure. This usually occurs when a layer inside the wall, floor, or roof falls below the dew point.

The symptoms of interstitial condensation
– Damp patches that appear without an obvious source of penetration
– Cold wall surfaces and reduced thermal performance
– Decay of concealed timbers, insulation, or masonry
– Mould growth in hidden or hard-to-access areas

How to evidence interstitial condensation
– Hygrothermal modelling of the building fabric
– Carbide meter / gravimetric moisture testing of masonry
_ Invasive inspection of insulation or concealed layers where necessary

How to resolve interstitial condensation
Improve vapour permeability by replacing non-breathable materials with breathable alternatives. Ensure that insulation and vapour control layers are correctly specified and positioned. Encourage balanced ventilation to reduce internal vapour pressure. Maintain consistent heating alongside effective ventilation to keep internal surfaces warmer and reduce the risk of vapour condensing within the fabric.

How not to resolve interstitial condensation
– By treating only the symptoms, such as repainting over damp patches
– By only applying lime internally and not resolving any related building defects
– By installing damp proofing systems that only temporarily hide / redirect the dampness else where.

Condensation (surface)

Condensation is currently the single most talked about form of dampness within British homes. One of the contributing factors is, that recent energy price hikes have caused home-owners to lower their central heating heat settings, and as a consequence of this there has been a rise in reports of condensation and mould growth.

Condensation is a complex matter, which is made even more so if you live in a solid walled heritage building, perhaps with little or no ventilation.

Ultimately we need to look at condensation from three angles.
1: Heating. Warm air is most definitely your friend when it comes to managing condensation as it both heats the walls (cold wall meeting warm air can cause condensation) and holds more moisture than cold air, therefore, it holds the water vapour so that it can be expelled via ventilation.

2: Wall temperatures. Condensation will struggle to form on a wall unless the wall is at or below due point, the temperature at which the water vapor turns into liquid water / droplets. Increasing wall insulation and ensuring that the wall is free from defects that may reduce its temperature are key!

3: Humidity. Moisture is always in the air, just at differing levels. As we live our daily lives we increase the water content of the air (humidity) within our home. The obvious contributing factors are cooking, bathing and drying clothes, however, the materials within your home also act as sponges and absorb moisture from within the air. Without the correct heating to draw moisture out of materials and into the air, coupled with suitable ventilation, the home’s humidity increases to the point of saturation / dampness.

The causes of surface condensation
My definition of surface condensation is where water vapour within the air of a property increases to a point where is forms droplets of water on cold surfaces (consider your bathroom walls after a shower) or, a process where the (wall) surface becomes cold enough to trigger the surrounding air to decrease in temperature and expel moisture onto that cold surface (consider a cold pint glass in the summer). They’re both the same process.

The symptoms of surface condensation
– Wet patches or patches on internal walls and ceilings
– Water running down the wall from the ceiling
– Excessive mould growth

How to evidence surface condensation
– Thermographic imaging for thermal bridging / dew points
– Psychrometric analysis – taking measurements of air temperature, surface temperatures, absolute humidity and vapour pressure.

How to resolve surface condensation in heritage buildings
(the suggested works will be dependant on the evidenced cause)
– Heat home to a constant 18-20 degrees
– Installation of kitchen and bathroom extraction fans to meet part F of building regulations
– Remedial works to fix any other form of damp within the home
– Opening windows to allow for air exchanges (last resort)
– Lime insulating plasters or renders for cold walls

How not to resolve surface condensation
– By applying non-vapour permeable paint / stain blockers
– By installing non-vapour permeable internal or external insulation
– By applying thermal or foil backed wall paper
– By installing a PIV unit which will only mask the symptoms of high humidity by a process of dilution

Summary

Self education is the single most important factor in ensuring that the time and money spent on maintaining your home is not wasted.

It is extremely important to note that moisture will always move through a heritage building, it cannot be stopped, but it can be managed!

I highly recommend seeking out information from a variety of sources and avoiding any company that might best be described as a ‘one trick pony’. By all means, after investigation and correct diagnosis you may wish to contact individual specialists. However, please understand that in most surveying and diagnosis cases, the tradesperson will more than likely diagnose the issue as the exact same problem that they just happen to sell a service for!

It is also important to mention that there is a false narrative within the heritage industry, that the installation of lime products alone will solve all damp issues, and this is most definitely not the case. Properties that we survey on a daily basis evidence this, having received full lime renders, pointing and plastering only to become ‘damp’ again over a period of 12-24 months because the underlying issues were not addressed. It should be noted that lime is often sacrificial in nature and may require removal and reinstatement as the building dries out, which could take 1-2 years after being previously being encased in cement, for example.

Often, extensive damp issues will only be resolved within a building through a combination of sympathetic repairs that work in synergy. Your journey to a dry and warm home that has been restored in a manner that will preserve its heritage authenticity should be viewed as a 2-3 years process, and not a simple quick fix renovation, that will sadly not meet expectations and waste financial recourses.

Information sources and training providers that I recommend

Ross Charters – Damp resolution expert based near Bath – Link

Russel Rafton – Dry Fix Preservation – damp resolution expert based in York – Link

Graham Coleman – Leading UK damp expert – Link

SPAB – The Society For The Protection Of Ancient Buildings – Link

Historic England – Link

Carrington Lime – training centre (highly recommended) – Link

TYWI – training centre – Link

Please note: all advice given by Truscott Building Preservation is specific to granite, slate and lime constructed buildings located in Cornwall only. It is important to note that buildings constructed in areas with less severe weather patterns and softer masonry types WILL require the use of very different techniques and materials. Our advice is not generic to the whole of the UK, and we suggest that you find a local expert who can best advise on the correct techniques and materials required to preserve your heritage building.