Ethos - Sealing Stone Marble, Granite, Limestone, Slate, Granite and Travertine Polishing and Restoration - London

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Types of stone sealant and how they work

There are a range of different sealers available from many different manufacturers with most falling into two main groups, Penetrating and Topical of which there are many variations for different uses.

Penetrating sealers:

Penetrating sealers, also known as penetrants or impregnators are thin liquids which penetrate deep into the stone. Their purpose is to block contaminants from entering the substrate of the stone while at the same time allowing it to expel interior moisture. They are therefore 'breathable' or vapour permeable.

Impregnators can either be solvent based or water based. The solvent or water is the carrier which takes the active chemicals into the stone. As the carrier evaporates the active ingredients in the sealer are left in the stone to do their job. Generally, we believe that solvent based sealers are more successful and longer lasting however due to health and safety regulations we are not always able to use these in a commercial environment.

Another choice which needs to be made is whether to use an oliophobic or hydrophobic product. An oliophobic impregnator will repel oil and water based liquids whereas a hydrophobic impregnator will only repel water based liquids. Many hydrophobic sealers are labelled 'oil resistant' however this only means they will slow down the absorption of oil while still allowing it to eventually enter the stone. We always recommend the application of an oliophobic sealer in kitchen areas where a range of different liquids are likely to stain and damage a natural stone. This type of sealer is also very useful in bathrooms where there can be a high concentration of body fats.

Topical Sealers:

These are sacrificial coatings which can be either strippable or permanent. Many are designed for resilient floors but will state that they are suitable for natural stone. Most of these are water based products which are made from polymers so that they can easily be removed with a compatible stripper. These sealers are much cheaper than impregnators and they do come with their flaws. Because the product is much softer than the stone, repeated applications can cause it to easily show scuff marks and high traffic areas will begin to show signs of wear. Application of these sealers will therefore complicate the maintenance cycle as periodical stripping and re-application will be required. Also, if the product is not UV resistant it will yellow over time. Its benefits include the fact that they offer a cost advantage over impregnators with some also designed to improve slip resistance.

Fluoropolymer Sealers & Polyurethane Coatings:

More recent products which have become available in our industry are sealers which are made from fluorocarbon alphatic resin. The manufacturers of these products will give very long guarantees however they are usually dependant on the stone being re-sealed periodically and maintained with their cleaning solution or preservers.

Sealers which we would never recommend are Polyurethane topical sealers. These are produced for sealing wood however many manufacturers will incorrectly state that they are also suitable for application on natural stone. They are not vapour permeable and so could cause serious damage to the stone. They will more than likely leave it with a very unnatural looking glaze and could also lower its slip resistance.

Urethane Based Sealers:

These sealers are usually solvent based and can also be described as 'permanent impregnators'. They are not to be confused with polyurethane coatings described above. They offer excellent protection for most types of natural stone but can be almost impossible to remove once dry. These sealants offer years of protection but are rarely used due to the difficulty in applying them correctly and their powerful vapours which can be dangerous if there is an absence of adequate ventilation.

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