Understandably many of our customers are unsure about what can or cannot be achieved. Here we wish to explain a little of the technical background to the services we offer. (The Late) Maurizio Bertoli, one of the doyens of the stone restoration industry who always put his customers first, famously used the adage ‘Education before any sale.’ This sentiment firmly underpins the ethos of our company.
An essential aspect of our services is sealing.
In general ‘Any Sealer is better than no sealer’. This applies especially to porous stones particularly marble, limestone, travertine and even some granite, which nowadays are often not ‘true’ in that these are not wholly impervious. Even porcelains and other ceramic surfaces may benefit from sealing.
Other materials, such as wood, are often sealed with a coating of a polyurethane product. This strengthens and protects the surface. Many other normally porous materials can be protected with a sealant that sits on the surface and acts as a barrier to penetrative agents.
Sealing a floor usually means applying an impenetrable barrier. For example, tiled floors are often sealed to give them added protection and make them ‘shine’. To achieve this a series of coats of emulsion polish are applied to the surface and allowed to dry.
The sealing of natural stone, such as marble, granite, limestone and slate, is significantly different. Natural stone is made up of crystals that interlock. The minerals that are present as crystals give stone its colour and striations. However, there are spaces between the crystals and the smaller these are the more compacted and less porous the stone is. These spaces determine the porosity of the stone. A combination of pore size and the mineral content of the stone also determines its hardness and durability. These spaces are air filled when the stone is dry and water filled when the stone is wet. Bacteria inhabit these spaces and are often vital for the maintenance of the stone. The little research that has been carried out into these suggests that bacteria are essential in maintaining the integrity of the stone.
Consequently we have a picture of stone being a complex mixture of minerals, bacteria and spaces. You could imagine the stone to be similar to a very hard sponge! If a liquid is dropped onto this it will be absorbed and spread through the spaces. This is why with stone what initially looks like a small spillage can end up as quite a large stain. To remove this it has to be flushed out of the spaces. A stone penetrating sealer simply fills up these spaces. Many of the stone sealants in use are based on fatty acids rather than synthetic sealants. These natural sealants are superior because they do not destroy bacteria but often stimulate them. Synthetic sealants destroy bacteria and have long-term consequences for the stone’s makeup. Nevertheless, sealants based on fat have a shorter lifespan and must be renewed periodically.
Sealants fill up the spaces between the crystals but do not cover the surface of the stone. Their purpose is simply to delay the penetration of liquids into the stone. So if corrosive materials are spilt onto the stone then it will become damaged. Stone sealants do not form a protective ‘seal’ on the surface of the stone. Therefore stone is only protected from absorbing liquids and is not protected from surface damage.