Following on from yesterdays topic I am going to discuss the importance of laying natural stone paving on a full bed of mortar. Many, many, many years ago I worked as a labourer for a garden design company in Stoke On Trent. A labourer will have to fulfill a whole host of tasks over the course of an average day on site, the list is endless. The most important job of a labourer though is to keep the person you are labouring for happy. The wheel barrow should always be topped up with mortar, paving slabs should never be more than an arms length away, required tools should be anticipated, the site should be kept clean and organised and most importantly the supply of tea should be regular. I have gone off track a bit anyway, lets get back to the point.
As a labourer I watched with interest as my foreman laid sandstone paving slabs on spots of mortar. It seemed like he knew what he was doing and the end result was always good. I have learned since that laying this type of paving in this way is flawed and the paving will not last more than a few years before it begins to come loose.
Indian Sandstone paving should always be laid on a full bed of mortar (4/5 parts sharp sand: 1 part cement, semi dry mix). As well as providing a stable solid foundation for the paving to sit on, using a full bed of mortar will create a vacuum making any movement of the finished paving very unlikely. It is also important to consider that imported sandstone & limestone paving, even if calibrated to a uniform thickness, will have cutting tolerances of up to 3mm. At the worst case scenario this could mean a thickness difference of up to 6mm between two different paving stones.
This highlights how installation methods have changed to cater for the boom in imported natural stone paving. Before the explosion in the popularity of imported paving the material of choice was always the cast concrete slabs, known affectionately as council flags. These flags were always 50mm thick so they could be laid on a dry mix of sharp sand and cement. The dry mix is not suitable for the imported stone because it is thinner and the thickness varies. Spots of mortar do allow for the variation in thickness but as earlier described do not provide long term stability. This means that the only way to lay natural stone paving is on a semi dry mix.