The Brew Cabin

It is about 6 months since my last question Tony on the laying of a large (100sq m) patio of Indian sandstone. Now some 3/4 complete, the parts of the patio laid last year have now been through their first winter and I have noticed that the mortar joint along just a few of the stone edges has developed a hairline crack as if the mortar has shrunk away from the stone.

These cracks aren't bad enough to do anything about at this time, and you have said before that such joints carry no stress, but I am wondering whether it is an indication of a bigger problem such as a fracture of the base. Indeed at one of the narrow points in the patio (1m width), looking at an exposed section through the structure (which is possible because there is an adjacent flower bed which has yet to be filled in) it looks like a crack has developed right through the foundation.

Structure details are: 75mm hardcore laid on very solid ground, 50mm concrete base and average 40mm full mortar bed at a 1:6 mix. Mortar is 1:4 with plain building sand. I didn't use any expansion joints (which may have been a mistake.)

I have some pictures which show both cracks and overall patio shape - but if you want to see them, can you tell me which e-mail address to send them to?

Many thanks.

Peter

Pointing nearly always cracks, I'm afraid. I still think it's one of the best options for jointing flags, but the minor cracking is a problem that's plagued us since we switched to cement-based mortars 80-odd years ago.

However, it's really not a big problem. The cracking can result from any of a number of reasons - there can be bed movement, as you suggest, but there is also thermal expansion/contraction of the stone and the mortar itself to consider, as well as natural shrinkage of a cement-based mortar. You could lie awake at night worrying about all the possible causes of mortar cracking, but, when you get up in the morning, the cracks are still there, yet the pavement hasn't actually fallen apart!

I really wouldn't worry about them, Peter. If they open slightly, you can fill any gap with dry jointing sand, and if, after a couple of years or more, any relatively wide cracks appear (let's say wider than 3-5mm) then a section of pointing can be cut out and re-done, but for now, and with the pavement being so young, I really wouldn't lose any sleep whatsover over a few cracks.

I'd like to see the photies, though - not that I'm worried about the cracks; I just love looking at photies of paving that folk have done for themselves! :)

info AT pavingexpert DOT com