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When stone cladding goes wrong
Many homes now use a combination of stone and brick cladding as finishing. Their simple design makes them a good canvas to carry brighter colours. PHOTO/www.gettyimages.com
What you need to know:
Stone cladding has become a popular finishing style in Uganda in the past few years. However, a number of homeowners have been disappointed when it has gone wrong, writes Phionah Nassanga.
When Henry Mutumba, a resident of Kitebi, Rubaga Division constructed his house 15 years ago, he finished his perimeter wall with stone cladding. For the first few years, it looked resplendent but as time went by, the stones fell off while others were washed away by rain.
Today he wonders what he should have done better to maintain the stone cladding in perfect condition.
Willy Kashokoozi an engineer at Reesi Consults says Mutumba’s stone cladding might not have been done or maintained properly after.
Using the wrong stone
When you think of stone cladding, the first thing to run into your mind should be the type of stone you want. Kashokoozi says choosing the right type of stone with the right shape is important. The next important thing is hiring a skilled stonemason (a person who cuts, prepares, and builds with stone).
“House owners and those that are planning to build should know that some stone cladding materials soak up water. Rainwater is often trapped between the stone veneer and the wall thus causing damage in the long run,” he explains.
For cladding, sedimentary rock is more likely to be used, because in general, cladding is only a thin veneer, and the surface of sedimentary rock, weathered and often showing wonderful colours, is plentiful and easy to work with. Another rock that is useful in construction is soapstone. It is a soft, durable rock that can be cut and polished, and can withstand high temperatures and moisture well.
Unskilled stonemason
As with all of life’s projects and jobs, the right team makes the dream come to life. As such, it is important to choose the right installer and team.
Rashid Ssenyonjo, an architect and civil engineer with HIL-Consult, says finding someone passionate, committed and experienced to help you bring your dream finishing to life is important.
“When researching and shortlisting your potential installer, I suggest you ask for testimonials and photos of previous projects that are similar to your requirements,” he says.
Noting that choosing the right stonemason is as important as investing in a quality stone product. They can either make or break your project, which is why it is important to do comprehensive background checks and research before committing yourself to a contract.
Wrong bedding
Kashokoozi says defects with stone cladding arise if the stone blocks are incorrectly placed in relation to its bedding plane. When placed on a wall, the stone should generally lie in its natural bedding position.
Kashokoozi explains that during installation, the stonemason should pay attention to the different layers, which should run horizontally in a manner in which the stone was originally formed.
However, incorrect cutting of natural stone across their natural bedding lines may force the stones to fall off since the stone is stronger in this position and less vulnerable to defects. When the stone is laid vertically, it is exposed to damage because the mechanical actions involved find it relatively easy to push off the bedding layers since there is no restraint from the adjoining stone.
Lime run-off
The soluble salts produced by the reaction between acid rain and the calcium carbonate in limestone can cause problems in adjacent materials. When the soluble salts are formed, they may run off say, a limestone coping onto a brick or sandstone element below. As these salts crystallise they can cause decay in materials that would otherwise not be particularly vulnerable.
Inappropriate mortar mix
Ssenyonjo says an inappropriate mortar mix can cause problems in both the mortar and stone.
“The major problem is usually related to having too strong a mortar because dense mortar allows less evaporation meaning any moisture in the wall will evaporate through the stone. And this may increase the chances and severity of salt-related defects to the building. When strong mortar is used, it is easily broken and may be vulnerable to shrinkage and cracking thus increasing the possibilities of rain penetration,” he notes.
Expansion of metals
Metal cramps have been used as fixing devices in stonework for many centuries. With these metal fixings, rust can expand and fracture the stone. Additionally, stone cavity walls may suffer the cavity wall tie problems.
Extraction and dressing
Stone can be damaged in the quarry if it is extracted by the use of explosives which may cause internal fractures. Damage can also be caused by excessive tooling of the surface of the stone.
Lichens
Lichens are a symbiotic association of fungi and algae. They are hardy in the sense that they are able to derive sustenance from a number of sources; the fungi element sucks out water and salts and the algae element manufactures food by photosynthesis.
Lichens can produce acids which may etch into the surface of stones such as limestones or calcareous sandstones. Finely carved stonework may be particularly vulnerable. The fine rootlets of some lichens may cause minor mechanical damage. The potential for damage is reduced by the fact that lichens are extremely sensitive to air pollution.
Advice
Kashookozi suggests that stone cladding that is suspected to be causing damp problems should be inspected and if it is defective it should be repaired. However, it is not usually possible to repair stone cladding,” cautions Kashokoozi.
