Etched in stone and in Guernsey tradition
Modern solutions to the age-old problem of damp mean that savvy buyers can invest in a period property with confidence, writes estate agent Trevor Cooper in his continuing series of property articles...
Modern solutions to the age-old problem of damp mean that savvy buyers can invest in a period property with confidence, writes estate agent Trevor Cooper in his continuing series of property articles...
CONTEMPORARY design may be the current trend, but the appeal of stone-built farmhouses is enduring. These impressive houses display superb craftsmanship, considering the tools and equipment of the time, and the inherent problems that have previously blighted older cottages and farmhouses need not concern today's careful house-hunters.
For example, these housing heavyweights often have shallow foundations little deeper than 12 inches. Early attempts at damp courses were ineffective or non-existent, resulting in damp rising by capillary action in external and even internal walls.
That old foe, however, is often wrongly accused. Sand from the beaches was typically used in the mortar that binds the granite and sea salt drawn out by heat can blister the plaster to form a fine, white fur.
Rising damp is also blamed for many defects when rain penetrating cracks in walls or broken pointing or through porous bricks can actually be causing the damage, as can ineffective guttering or broken roof tiles – the same as with any building.
Chimney stacks are notorious for leaking water if the flashings (where the chimney stack joins the roof) are little more than slate embedded in cement. The cement shrinks as it dries, leaving hairline cracks for rain to slip into over many years. Count the number of tall brick chimneys that lean towards the sun because the cement pointing has dried and shrunk on one side quicker than the other.
Chimneys on houses with thatched roofs have 'drips' built into them. The thatch is tucked underneath extended bricks that deflect the rain away from the join between the thatch and the chimney stack. 'Drips' can still be seen on some Guernsey houses with slate or tile roofs that were once thatched.
Nowadays, lead 'trays' or lead 'stepped' into chimneys effectively stops moisture sinking into the chimney breast or under the roof.
Moisture is always present in granite walls because granite is not only one of the toughest stones, it is also surprisingly absorbent. The amount of moisture retained in the walls actually determines the level of a problem. In theory, and usually in practice, any dampness absorbed over a wet winter is dried out during a hot summer, stressing the importance of allowing granite to breathe.
It became increasingly popular at the turn of the 20th century to render the facades of stone-built houses, using a lime-based plaster to protect but not suffocate the stone. This was not only a practical application but also highly fashionable at the time.
Further modern solutions can remedy the historical problem of damp in walls, rising or penetrative.
Electro-osmosis is considered to be a modern form of damp-proofing, yet it was actually discovered 200 years ago in an experiment using positive anodes and negative cathodes to reverse the polarity of capillary action. The Swiss first developed a system in 1930 of applying electro-osmosis to dry out foundation walls.
Rentokil introduced it to Britain and, between 1962 and 1974, it was used in more than 55,000 houses, before the advent of injected damp-proofing systems.
For this, chemical damp-proofing fluid is pressure-injected into the wall. A similar method is to insert tubes or frozen sticks of the fluid into the drilled holes and allow them to diffuse gradually.
The growth of the green movement, however, has seen a resurgence in the use of electro-osmosis systems as a chemical-free damp-proofing option. It consists of titanium or copper wire being installed in mortar joints near the base of the affected walls and a low-power electrical charge applied.
The Building Research Establishment has reservations about its effectiveness and states the obvious by saying that a physical damp-proof course is the only completely sure method.
A physical damp-proof course has been a building requirement – or recommendation – since the 1870s. This was initially a horizontal layer of overlapping slates forming a continuous barrier at the base of the wall, replaced in the 1930s by bitumen, and now a mainly plastic damp-proof membrane resembling bitumen.
Tanking is another option, although best used against concrete. Tanking is a liquid coating, often epoxy or polyurethane, that hardens to seal the whole floor and walls usually to a metre above external ground levels – creating, in effect, a tank within the room.
Before resorting to any retro-applied form of damp proofing, however, damp issues should be looked at externally. Check that guttering, soakaways and drains are not allowing water to collect, or pond, against the house. Reduce ground levels and install land drainage channels to prevent moisture bridging external walls and being drawn inside.
Inadequate sub-floor ventilation can also cause dampness in walls. A build-up of moisture in the floor void condenses on exposed masonry and timbers, even above an existing damp-course, resembling rising damp internally. Air bricks will ensure there is an adequate through draught to remove moisture from the void, reducing moisture levels in floor timbers and reducing the risk of decay and infestation.
Let it not be overlooked that modern building techniques are also equal to rampant forms of rot and beetle issues that have cursed older cottages and houses in the past.
The message is that while on-going maintenance is necessary with older houses, practically minded purchasers can rest assured that qualified expertise and lateral thinking can ensure the character cottages and magnificent farmhouses that have stood for 150 years or more will outlive us all, to the delight of most and the joy of those lucky enough to live in them.
