The where the what and the how of selecting stone…..

Selecting the right stone for your project requires some careful consideration of the where, the what and the how. Given the changing political landscape, you may also want to consider UK quarried stone ahead of imported stone. Unless they are in stock in the UK you might find your stone at the back of a very long queue of lorries in Calais.

There are a great many UK sandstones, slates and limestones from which to choose. Less granites and no marbles, unfortunately. The Stone Federation of Great Britain represent many quarries  through their quarry forum and have a wealth of knowledge on types and locations. As does The Stone Specifiers Source Book, also produced by the Stone Federation.

Marble, granite limestone, slate, basalt, sandstone, quartz – there is a vast pallet of natural stones from which to select the right stone for your project, large or small. Colours are a good starting point, but you will definitely want to consider how the chosen material is likely to perform in the location.

For instance, bathrooms need to be beautiful, functional and easy to maintain. Most Limestone and Marble is formed with a high proportion of calcium carbonate, which is soluble. It doesn’t mean the stone will dissolve underwater, but some will be more susceptible to water staining. If water softeners are being added to filtration systems, it is worth checking if the contents will affect the stones surface and increase limescale build-up or contribute to deterioration of the stone surface.

Stone floors in receptions and kitchens should be hard wearing and relatively easy to maintain, providing you use the correct cleaning regime. I know of a  stone cleaning company to be found regularly in the foyers of some of the top hotels in London at 4am in the morning. Almost silently, machine cleaning the floors to their original condition, some weekly, some fortnightly, all with excellent results.

There are many occasions where I am asked to visit  “problem” floors to report to the client on the condition and why their floor looks so poor after a relatively short life span. Invariably, amongst other issues, the cleaning regime leaves much to be desired. The 4 am cleaning shift is often a man with a bucket full of dirty water and an old mop. This only serves to move dirt around the floor rather then remove it.

Use pH neutral cleaners and make sure they are suitable for stone. Clean regularly and  aim to have surfaces professionally cleaned at least every 18 months. Removing dirt and any limescale build-up will keep the stone fresh and prevent long term damage.

Sealing stone is not really sealing. It is not like a varnish for wood. The real name is impregnator. These come in two types – water based or solvent based. The solvent based impregnators last longer but less environmentally friendly. The impregnator sits below the surface and should prevent deep staining. You still  need to wipe spillages off the surface as quickly as possible – particularly wine and acidic liquids – but it does help to provide a barrier against deep staining.

Other than cleaning, give careful consideration to the type of stone and where it is being used. There are a couple of key areas to investigate for your chosen stone.

Slip and Abrasion Resistance values.

Slip resistance tests were originally developed as a rubber pendulum test by the Greater London Council, published in 1971. Today, a 4S pendulum test is recommended, with a 96 hardness rubber to simulate ordinary pedestrian foot traffic for public areas and 55 hardness rubber to simulate bare foot traffic – more suitable for pool surrounds and wet bathroom floors. The HSE  expect a minimum value of 36 in the wet or dry, as I suspect will you or your client’s insurance company.

The surface finish will affect the test results – a sandblasted face  presenting the least potential for slip and a highly polished floor the most.  If there is heavy footfall on the floor, even if it begins as  honed, it may end up as polished with time and footfall.

Therefore, abrasion resistance test results will help to understand the likely wear capability of the floor. Results are expressed in mm and BRE guidelines suggest anything under 23mm of wear is suitable for intensive use, 23 to 30 medium use, 30 and above domestic use. You will need to understand  the predicted footfall to decide which category your floor falls into.

Floor loading is another factor to consider. Floors that are expected to carry the weight of cars, for instance, will require a stone with a high flexural strength and possibly thicker than you would have expected, to carry the additional load, however infrequent.

There are coatings on the market that claim to improve a stone floors slip resistance. But always check the on-going maintenance requirements and costs and any warranty offered.

Flexural strength and slip resistance results can be found on the CE marking certificate, which should be obtained from the supplier of the stone. As long as we are in the EU it is their responsibility to provide this to the buyer. Abrasion resistance tests do not have to be declared on the CE certificate for external or internal floors, but I would suggest these are checked before specifying the stone.

Then there is underfloor heating, sub floor preparation, waterproofing and installing the stone……..

Stone is a fantastic product and elevates design to a luxury level. Just make sure you do your homework on the where the what and the how.

Robert Merry is a member of the Technical Committee of the Stone Federation of Great Britain. His company, The Stone Consultants, are an independent stone consultancy who offer advice and guidance on stone related issues to the construction industry including technical specifications and expert witness.  M:07771997621


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