Marble and Limestone have been used as counter top or work surfaces for hundreds if not thousands of years. However in recent times there has been a renaissance in their use. They have become fashionable. However it seems many clients are totally unaware of how they perform in this environment and how they should be maintained.
Expectation vs. Reality:
Clients more often than not select polished marble and limestone thinking that the polish is a seal. However they could not be further from the truth. Marble and Limestone are made up of predominantly calcium carbonate. This is a soft mineral that is easily dissolved by common household dilute acids such as orange juice (citric acid), milk (lactic acid) to name but a few. The stone is not protected by the polish. Instead the polish will be attacked by the acid leaving an etch mark. The stone is also porous hence the acid will also be absorbed into the stone creating below surface staining. The reality is that Marble and Limestone need special care and maintenance to become the practical work surface the client expects.
Protection and Maintenance:
With calcium stone exhibiting two major characteristics – porosity, causing staining and acidic sensitivity – the first step in maintenance needs to be protection. Although sealer technology has come along way over the years there is no simple multi-purpose sealer that will protect universally. Instead we have to address each characteristic separately.
The porosity in a marble or limestone is the easier of the two characteristics to address. The application of a penetrating or below surface sealer reduces the porosity to a level where you have a long period of time to remove any spillage. There are many different types of penetrating sealers on the market however they will differ mainly in how much protection (measured in the time they will protect and the range of contaminants they will repel) they give you. The low cost products will measure protection in minutes with a small range of contaminants where the premium products will afford much greater protection (measured in hours) against a quite exhaustive range of contaminants. So as you can see the issue of protecting marble and limestone from below surface staining is easily addressed. However porosity is not the only issue.
This is the most difficult characteristic to overcome. The first important point to clarify is that penetrating sealers DO NOT protect the actual working surface. It is a common misconception. To give you an example, when you drop orange juice on to a piece of polished marble the sealer will repel the juice stopping below surface staining. The stone will not turn orange. However it will not stop the citric acid in the juice attacking the surface calcium leaving the polish etched and damaged. The resulting etch is similar to a scratch in polished timber. To remove a scratch in timber you need to sand and re-polish it. The same is true for the marble. Etching cannot be “cleaned away” it has to be re-polished!
So how do you address this acid sensitivity?
There are three answers that in turn require the client to make a choice. Firstly you can apply a coating sealer. This would appear to be the most obvious answer. However the sealers that can be applied to a dense smooth surface such as limestone or marble have to be thermoplastic. This means they are applied using a buffing machine that generates the heat required for these sealers to both bond and spread without showing application marks. The maintenance involves frequent buffing of the coating something that is not always practical for a client.
The second solution is to live with an exposed polished surface (applying only a penetrating sealer) and to re-polish the surface when required. This involves polishing the surface with chemical compounds again using a buffing machine. It is much slower and more expensive than a coating and is again usually not considered practical especially in domestic installations.
The third solution is to do with stone selection. I have only mentioned polished stone so far. However there is another finish available, that historically was used more for work surfaces than polished, called honed. The surface is still very smooth but does not have the highly reflective nature of the polished version. The advantage is that acid etching is not nearly as visible making the maintenance of the stone easier. In short a penetrating sealer is all that is required.
It must be noted that one of the benefits of polishing is that it helps full colour development. In other words the colour of polished stone is more intense. However even this can be addressed now that penetrating sealers (which are usually invisible) are available in enhancing formats. These new products give the colour developed by polishing without the actual surface shine that is so easily damaged.
Daily or routine maintenance is the easiest question to answer. All marble and limestone is alkaline as are all of the adhesives and grouts used to install the stone as well as all of the sealers (penetrating or coating) used for protection. Therefore daily cleaning should be done using only ph neutral cleaners. These will not damage the stone or components used to install or protect them. Acids (even dilute acids such as vinegar) should not be used, as these will damage the stone especially the polished versions. They can also cause long-term damage to sealers, especially coatings and low cost penetrating sealers.
It is a fact that Marble and Limestone are currently fashionable especially for use on vanities and kitchen counter tops. They can make a very practical and durable work surface. However as shown above polished stone will only perform to expectation if a proper and regimented program of maintenance is adhered to. Another alternative is to use a honed version of the same stone. This will perform with a much more simplified maintenance program and in many cases will better meet performance criteria as well as satisfying the aesthetic requirements of the customer. I do not think it is a coincidence that for centuries polished stone has been used mainly for decorative walls and floors and honed for work surfaces such as benches and heavily trafficked floors. I have no doubt they had the same expectation as today’s clientele, so I recommend we let history teach us a lesson well learned and tested over time.