Colours Leaching in Butt Jointed Sandstone
There are several reasons why butt jointing natural stone paving is not recommended (see Butt Jointing Natural Materials) for potential physical damage during laying operations and freeze/thaw issues, but there is another reason for not recommending close proximity designs when planning patio projects.
One particular scheme in North London, on a very prestigious site, the designer used 50mm deep 900mm x 900mm sawn six sides natural sandstone in a buff colour. Each of the four corners were removed at an angle, so that when four slabs were placed together, a small empty square was the result. Everything was very formal, with straight lines and right angles, with care taken to ensure water run-off leaving no problems with water retention causing minor puddles creating areas of algae or static detritus.
The slabs were not pre-sealed, and as they were literally, touching on every side, there was no way of grouting the project, certainly no joint was greater than 2mm. The plan called for a different colour sandstone inset ‘diamond’ slab, 100mm x 100mm x 50mm in an orange/red colour, laid between the four corners where the chequer-board pattern met.
The paving had only been laid for a few days, when a reasonably heavy rainfall occurred overnight, with the result that the orange/red sandstone inset had fused or leached from the diamond, discolouring the buff paving slabs.
After a couple of weeks, the whole project was condemned and replaced. Luckily, it was the Main Contractor’s project, not the landscapers… A lesson learned at no personal cost.
It was never established whether it was the effects of salt displacement or other chemical reaction, as the client was not interested in finding out what went wrong – he simply wanted a different design in the end.
