Learn how to choose a stone sealer: what you should consider, why sealers don’t provide complete protection from staining, and what test methods are used to assist sealer selection.
Article: Jim Mann
A crucial part of the care and maintenance practice for many stone types is the use of a sealer to improve the stone’s resistance to staining. When you are met with the wide range of sealers on the market, selecting the right sealer for the job can be daunting. You might wonder how to choose a stone sealer that’s appropriate for your requirements. ‘Do I choose a surface sealer or an impregnating sealer?’ ‘Do I want a wet-look finish or a natural finish?’ ‘Do all stone surfaces need to be sealed?’Â
Stone is possibly the most versatile of construction materials. We can build with it, walk on it, bathe in it and even eat from it. Advances in modern processing methods have made stone accessible to everyone. The ubiquitous use of stone throughout our homes, workplaces and public spaces has also brought the need for updated cleaning and care regimes to maintain its beauty.
What kind of sealer should be used on natural stone?
As stone is a porous material, it can absorb bacteria, liquids and dirt over time, leading to staining. The application of a sealer is often a practical method of improving the stone’s stain resistance.
When choosing a stone sealing system, you need to consider the stone type, surface finish and location. Most importantly you need to know what you are protecting your stone from. As an example, a light grey granite on a restaurant floor will be exposed to red wine, coffee and oily foods. The sealed surface will also need to have adequate slip resistance to meet statutory requirements. In this case an impregnating sealer would be best suited, as this group of sealers does not significantly alter the slip resistance of the surface. Choosing a sealer with good oil repellence would also be important, as grey colours tend to highlight oil stains.
As topical sealers are not vapour permeable (breathable), they should never be used on stone finishes if there is a chance water will be present as this may lead to delamination of the sealer and deterioration of the stone. See To seal, or not to seal? Why good stone can turn bad, where we go into more depth about the selection, use, benefits and limitations of stone sealers.
Test method for evaluating stone sealers
Stone Initiatives has developed a stain-resistance test method (SI-STAIN-18) specifically for evaluating sealers on dimension stone. The test results provide you with information on the natural stain resistance of the stone when exposed to a range of common staining agents and its performance after sealers have been applied. The test covers resistance after a long term (e.g. if the surface was only cleaned once per day) and short term dwell time (if the spill was clean up relatively quickly).
Understanding the limitations of sealers
Understanding the limitations of sealers is also important. Sealers are designed to improve the natural stain resistance properties of stone – they will not provide 100% protection against all stains in all situations. As an example, an impregnating sealer will not prevent marble or limestone being etched by acidic solutions such as wine or soft drinks; impregnating sealers are designed to reduce the absorption of stains and cannot provide complete protection to the exposed surface. Surface sealers (such as acrylics and polyurethanes) provide excellent surface protection by forming an impermeable barrier. The drawback of this feature is that any moisture below the sealed layer cannot escape and peeling of the coating may follow.
Maintenance of the sealed surface is also an important factor. An application of sealer won’t usually last the lifetime of a stone surface, and regular maintenance and monitoring is required. The frequency of application will depend on the location and traffic type.
As a guideline, a sealer applied to a premium floor should be assessed on an annual basis. A simple assessment tool is to determine the rate of absorption of droplets of water. The test usually involves placing droplets of water on the surface and wiping them off the surface after 5, 10 and 15 minutes. Any darkening of the stone will be due to the absorption of water and indicating possible degradation of the sealer. See more in our article Top tips for cleaning stone floor finishes.
So how do you choose the right stone sealer? In summary, selecting the correct protection system for your stone really depends on the type of stone, its surface finish and where/how it will be used – there is no one product that will work in all situations or for all types of natural stone. A first step is to engage a professional laboratory such as Stone Initiatives to determine the stain resistance of the stone 1. without a sealer, and 2. with a range of sealer products. This will provide insight into the performance of the stone and can ensure you choose the right sealer product.
Contact us for more information in how to choose a stone sealer for your project.
This is an updated version of an earlier article published by Stone Initiatives, titled Sealer Selection Guide: An Introduction.