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In this regular column, Consultant Barry Hunt answers reader enquiries. If you have a question, email it to: nss@qmj.co.uk marked for Barry’s attention
Q: What amount of repair or fill to a stone is acceptable?
I would not consider the rejection of a large kitchen worktop because of a repaired small chip on an edge reasonable because occasional small chips are difficult to avoid in such large pieces of stone. However, the repair of such chips must be of high quality.
The question as to how big a repair can be depends on the stone type and finish, but generally the larger the crystals and the more highly polished the finish the easier it is to hide a repair.
If a stone is cracked at a corner, this may provide good cause for rejection. But if the stone is of a type that exhibits lots of veining, the repair can be made to match one of these veins and, carried out correctly, can be difficult to detect and thus acceptable.
However, such a crack repair should not be undertaken if the stone is to perform any form of structural function rather than be purely decorative.
Stone edges are always at risk of damage but often when jointed the grout helps to hide or lessen the impact of some of the larger edge losses and this is generally acceptable.
The natural variation of stone and the processing procedures it is subjected to mean that many stones exhibit small but acceptable flaws. If we rejected stones because of these flaws, the stone would simply never be used or would cost considerably more because of the greater waste, which is something that is difficult to justify in today’s ecologically sensitive climate.
This is why stone samples for acceptance must be viewed at a distance of at least two metres, which is just above the minimum distance that most stones are viewed when in service, our eyes being on average around one-and-a-half metres above the ground.
The only time this criterion should not be applied is for kitchen worktops, which are the most closely viewed and intensively used pieces of stone by the most critical people – proud kitchen owners.
Many stone slabs or tiles, particularly limestones, have resin applied to their surfaces in the factory as standard. The resin is often difficult to find as it typically fills what are small holes.
For the most part this resin remains sound. However, in some instances holes that are quite large and/or shallow have the potential for the fill to fall out in-service.
Travertines are a special case as they are often highly voided but extensive filling is considered acceptable. This is best carried out when travertine is cut across the bedding (vein cut).
However, when cut with the bedding (cross cut) the fill can become quite extensive and shallow and prone to failure. Travertine termed ‘classico’ has been cross cut.
In the sale of any stone the seller should ensure that the purchaser is fully aware of the presence of repairs or fill materials and there must be agreement on the type, size and number of these features that are acceptable.
It must also be remembered that if a stone is filled any test declarations made in accordance with the European standard may not apply if the tests were carried out on unfilled materials. And vice versa.
In particular, stone would not normally have to be put through fire testing as it is considered to be non-combustible, but the use of organic resins for fill may dictate otherwise.
Reference
BS EN 12057:2004. Natural stone products – Modular tiles – Requirements. Published by the British Standards Institution, London.
The advice offered in answer to readers’ questions is intended to provide helpful insights but should not be regarded as complete or definitive. Professional advice should always be sought with all stone-related issues as each problem will inevitably have its own unique set of circumstances.
Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646
Q: What amount of repair or fill to a stone is acceptable?
I would not consider the rejection of a large kitchen worktop because of a repaired small chip on an edge reasonable because occasional small chips are difficult to avoid in such large pieces of stone. However, the repair of such chips must be of high quality.
The question as to how big a repair can be depends on the stone type and finish, but generally the larger the crystals and the more highly polished the finish the easier it is to hide a repair.
If a stone is cracked at a corner, this may provide good cause for rejection. But if the stone is of a type that exhibits lots of veining, the repair can be made to match one of these veins and, carried out correctly, can be difficult to detect and thus acceptable.
However, such a crack repair should not be undertaken if the stone is to perform any form of structural function rather than be purely decorative.
Stone edges are always at risk of damage but often when jointed the grout helps to hide or lessen the impact of some of the larger edge losses and this is generally acceptable.
The natural variation of stone and the processing procedures it is subjected to mean that many stones exhibit small but acceptable flaws. If we rejected stones because of these flaws, the stone would simply never be used or would cost considerably more because of the greater waste, which is something that is difficult to justify in today’s ecologically sensitive climate.
This is why stone samples for acceptance must be viewed at a distance of at least two metres, which is just above the minimum distance that most stones are viewed when in service, our eyes being on average around one-and-a-half metres above the ground.
The only time this criterion should not be applied is for kitchen worktops, which are the most closely viewed and intensively used pieces of stone by the most critical people – proud kitchen owners.
Many stone slabs or tiles, particularly limestones, have resin applied to their surfaces in the factory as standard. The resin is often difficult to find as it typically fills what are small holes.
For the most part this resin remains sound. However, in some instances holes that are quite large and/or shallow have the potential for the fill to fall out in-service.
Travertines are a special case as they are often highly voided but extensive filling is considered acceptable. This is best carried out when travertine is cut across the bedding (vein cut).
However, when cut with the bedding (cross cut) the fill can become quite extensive and shallow and prone to failure. Travertine termed ‘classico’ has been cross cut.
In the sale of any stone the seller should ensure that the purchaser is fully aware of the presence of repairs or fill materials and there must be agreement on the type, size and number of these features that are acceptable.
It must also be remembered that if a stone is filled any test declarations made in accordance with the European standard may not apply if the tests were carried out on unfilled materials. And vice versa.
In particular, stone would not normally have to be put through fire testing as it is considered to be non-combustible, but the use of organic resins for fill may dictate otherwise.
Reference
BS EN 12057:2004. Natural stone products – Modular tiles – Requirements. Published by the British Standards Institution, London.
The advice offered in answer to readers’ questions is intended to provide helpful insights but should not be regarded as complete or definitive. Professional advice should always be sought with all stone-related issues as each problem will inevitably have its own unique set of circumstances.
Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646