Natural Stone Calibration

To calibrate or not to calibrate, that is the question!

I often respond to queries on the forum at paving expert.   I recently gave my opinion on Calibrated Indian sandstone to a concerned customer who had purchased 22m calibrated fossil mint sandstone.  The customer was especially concerned that the 900 x 600 x 22mm would be to fragile.  To see my reply please check out the following link:;act=ST;f=2;t=7959

Read on for an honest appraisal of calibrated natural stone.

Q.  Why is calibrated stone suddenly on the radar?

A.  The Indian stone suppliers and manufacturers can charge more to the importers if the stone is calibrated.  Also the stone importers can also squeeze more material into a container which reduces transport costs.

Q.  Is there any reason why generally the stone is calibrated to 22mm?

A.  The reason for this is economics for the importer.  If the stone was calibrated to say 25mm 0r 30mm then the importer would still be paying more to the manufacturer for the calibration service but would not be making any savings by benefiting from being able to stuff more  material into a container.

Q.  Is 22mm thick stone strong enough for my patio?

A.  This is a very interesting question which has many answers.  It's widely recognised that the most important factor when considering the strength of a driveway or patio is not the paving material itself but the sub base underneath, that's the first school of thought.  We must also remember that all natural stone is subject to dimensional cutting tolerance.  This means that although stone is sold as 22mm the actual thickness range could be 20-24mm.  Also certain types of sandstone are extremely hard, for example raj green & kandla grey.   While fossil mint is one of the softer varieties of Indian sandstone.  We also must consider the application and how much traffic the paved area is expected to receive.


There are many factors to consider when deciding whether or not calibration is right for you.  If the paved area is going to receive high traffic it will be safer too avoid 22mm calibration.  If the stone is one of the softer varieties like fossil mint then you should also avoid 22mm calibration.  Overall our opinion is that 22mm stone is not thick enough for the rigours of a modern day patio

By London Stone Blog | Published 24th May 2010
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