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18 May 2020
Nothing quite matches natural stone construction for aesthetic charm and durability. There is something profoundly authentic and enduring about a building, quarried from the landscape in which it stands. Whether it is soft Cotswold stone or iron hard Aberdeen granite, these materials blend naturally with their local surroundings, so that the building is almost a natural extension of its environment. However, stone like all minerals is ultimately vulnerable to weathering and such erosion by wind, water and frost takes its toll over time.
Damp or moisture ingress is the most common problem afflicting stone-built properties in our wet climate. Leaving aside “rising damp” which typically derives from DPC failure, it is “penetrating damp” which is the biggest source of problems by far.
“Pentrating damp” is what happens when your walls stop shedding water and instead absorb it, like a sponge. This is usually a gradual process of decay which typically takes many years.
But why does this happen….?
In calm, windless conditions, rain falls more or less vertically and has minimal contact with the walls of your home. But in stormy weather the wind drives rain sideways, gradually soaking the walls to refusal. In the U.K we frequently see multiple low pressure fronts stacked up out in the Atlantic, which roll in week after soggy week, as if on a conveyor belt. This constant rain mimics immersion because the wall never gets the chance to “dry out” (evaporate) and there is pressure from the wind, driving the rain into the substrate.
Of course most of the rain simply runs off, but some of it is absorbed deep into the stone or mortar joints and it is this which does the damage. Soft materials like the jurassic limestone of the Cotswolds or Yorkshire sandstone have microscopic capillary channels which are especially susceptible to absorbing moisture. Finally the moisture saturates the capillaries and emerges as damp patches on plaster inside your home.
Wet stonework and mortar joints are vulnerable to damage from the freeze/thaw cycle. It is well known that water expands as it freezes and this applies equally to water absorbed in your stonework. Just as a glass bottle may shatter when the liquid inside freezes, your stonework surface will crack as water trapped inside expands. Over time this leads to “blown” faces, crumbling mortar joints and further water ingress which then freezes and exacerbates the destructive cycle.
Some stone is naturally “porous” which means that the geology of the rocks includes natural micro-channels through which moisture can pass. In addition some stone becomes porous over time through the cumulative effects of the freeze/ thaw cycle.
Mortar joints are a common weak point for moisture ingress in stone walls. Older buildings were often constructed using lime mortar which has the great advantage of being soft and breathable which in practical terms means it can absorb movement from the expansion and contraction of other materials such as stone and timber, without cracking. However, lime mortar does not perform well in persistent and prolonged wet spells because it is highly absorbent and will just keep absorbing water for as long as water is thrown at it. This water eventually arrives as damp patches on the indoor plaster finishes.
Portland cement mortar joints can also pose problems but for different reasons. Although Portland cement has superior moisture resistance, it is harder once cured than many soft stone types so does not yield in expansion / contraction leading to cracks in the mortar and in some cases the stone.
Where stone walls meet hard standing (tarmac pavements, paved driveways, patio flags etc.) the phenomenon of “splash back” occurs, whereby rain droplets crash into the hard standing and splash up the adjacent wall. With sandstone in particular this causes the walls to soak through at a much faster rate than they might otherwise and in the case of buildings beside roadways, corrosive de-icing salts (grit) exacerbate the surface deterioration. This is often mis-diagnosed as rising damp because it occurs lower down the wall.
All of these issues result in penetrating damp which degrades plaster and decorative finishes in our homes and also causes secondary problems with dry rot, mould growth and poor air quality. But to effectively combat the problem you need a sealer which will stop the saturation without compromising the ability of the stone to wick moisture away.
For this reason “Kingfisher” has developed a range of fully micro-porous or breathable stone and brick sealers. “Extreme Climate”, “Superseal” and “Stormseal” are all pore liners, not pore blockers, which means that they repel water droplet molecules but still allow water vapour to escape. These highly effective professional treatments are the best and most cost effective way to protect your stonework from damp without trapping moisture in the substrate.
So, whether it is dampness coming in around a window reveal, your chimney breast or an exposed gable wall, Kingfisher Building Products has the experience to help you diagnose the problem correctly and the products to resolve the problem without ever compromising the breathability of your walls.
