The Brew Cabin

As everyone says Tony - an extremely good site!
A couple of minor questions if I may. I'm laying a fairly large (75sq m) patio of Indian sandstone on a concrete base with an average 40mm mortar mix at 6:1. In my first few stones, not knowing any better, I used the 5 spot method, although they were very large blobs which mostly merged together when tamped down. Having read you site however, I'm now on the full mortar bed but those early stones (only about 6) plus one or two of the larger later stones (1.2m x 0.56m) have a hollow sound when you tap them.

I found your archive post which describes the problem and my question is simple. Would you recommend taking these up and relaying or would you leave well alone until something goes wrong? They appear very firmly fixed at present and the large ones are a devil to do!

Second question on the learning curve: I used my 6:1 mortar also for pointing on those early stones but then found your recommended mix of 4:1. Again, am I likely to have problems with a 6:1 mortar in due course, or is it just a case of wrong, but not that wrong?

I think I'd leave the spot-bedded flags for now, Peter. It may well be, as you say, that the mortar dabs merged to some extent, and are supporting the flags adequately (for foot traffic). Lifting and relaying may not achieve anything other than getting rid of the hollow echo.

The pointing is slightly more problematic, because the difference in strength between the 6:1 and the 4:1 may make itself apparent as a colour difference. Strength-wise, I wouldn't worry because mortar-bedded flag paving relies on the bedding for its competence, and the jointing is primarily a matter of "filling a gap", unlike other paving types, such as cubes or cobbles, where a large part of the pavement's structural integrity results from the jointing strength.

So, unless there's a glaringly obvious colour diff between the two mixes, leave it alone. Any minor shade diff will disappear as the mortar weathers, and, looking out of my window, now really isn't the time of year to be doing more pointing than is absolutely necessary!

I have a sneaking suspicion that the above is what you were hoping to hear! :)

Thanks for the very prompt and comprehensive reply Tony - and yes, it was the right answer in both cases! The pointing mortar colour is a little different but as you say, it will weather.

I will continue with renewed confidence - though I am amazed how long it all takes as a result of which I am indeed doing laying and pointing in these dismal days.

Sorry - a couple of more questions Tony:

I was cutting an awkward shaped stone today and the last cut (it is always the last cut) resulted in a hairline fracture down about one third of the stone length and visible on both sides (with close scrutiny). The stone seemed otherwise sound so I laid it anyway. Do you think that the stone will eventually crack - possibly as a a result of water ingress and subsequent freezing - and therefore is it best to replace it sooner rather than later?

Second question: in cutting a large curved edge to a patio, is it better to lay the stones and cut 'in situ' or dry lay first and cut individually before bedding?

Thanks once again!

If a hairline fracture is showing on both upper and lower faces, it can only be a matter of time before it breaks completely. Once the frost gets into it - blam! If you can get a replacement flag, you might as well get it changed asap.

When it comes to cutting a large radius curve at a free edge, I'd much rather lay all the flags and then cut in-situ. If you do a dry lay, mark and then cut before final bedding, you can guarantee the abstrads won't align that way again and you end up with a dog-legged curve!

Great - thanks again Tony!