Hi, having figured out how to drain my planned patio, I'm now wondering about the bed thickness. I've read and re-read your guidance but have to confess to still being unclear. I'm planning to lay Stonemarket Yorkstone octagonal system slabs which I gather are nominally 37mm thick. You suggest a screed of sharp sand and cement and advise against the five point mortar dab approach. Elsewhere, you recommend making an allowance of a few millimetres (10-15 I think)
so that the slabs can be settled down to the correct level. Two questions : if I use the sand and cement screed will this still require the settling allowance or is this just needed when using sand only? Secondly, if I don't use the 5 dabs of mortar, do I use any mortar at all? I fear these questions reveal my painful ignorance but, as ever, your advice is much appreciated.
sand and cement bed thickness
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84-1093879891
Chris asked....
if I use the sand and cement screed will this still require the settling allowance
Yes, it will, but only trial and error will determine just how much is required. The Stonemarket flags, along with many other cast flags, vary in thickness, and so a screed, while being useful, will not be 100% reliable. The claimed 37mm nominal thickness means they will be anywhere between 32mm and 42mm, and could even be 32mm thick at one edge and 42mm thick on the opposite edge.
However, you could prepare a screed, and then adjust as required with extra sand/cement for those flags that prove to be a little thinner than ideal. Even with a screeded bed of sand/cement, you still need to consolidate the flags once they're in position.
if I don't use the 5 dabs of mortar, do I use any mortar at all?
Only for pointing. :)
if I use the sand and cement screed will this still require the settling allowance
Yes, it will, but only trial and error will determine just how much is required. The Stonemarket flags, along with many other cast flags, vary in thickness, and so a screed, while being useful, will not be 100% reliable. The claimed 37mm nominal thickness means they will be anywhere between 32mm and 42mm, and could even be 32mm thick at one edge and 42mm thick on the opposite edge.
However, you could prepare a screed, and then adjust as required with extra sand/cement for those flags that prove to be a little thinner than ideal. Even with a screeded bed of sand/cement, you still need to consolidate the flags once they're in position.
if I don't use the 5 dabs of mortar, do I use any mortar at all?
Only for pointing. :)