I have a quantity of old sandstone, in which I will be building a low- ish garden wall. The stone came originally from a mediaeval church window, but has since been cut down to blocks that one or two chaps can lift.
For longevity, should I be considering using lime mortar in this construction, rather than using hard cement around soft sandstone?
I've also got nice old weathered faces, and harsh machine-cut faces to some of these blocks. Any ideas on a quick-ish method to soften the machine-cut faces?
Around here in North Norfolk, the very soft yellow-brown sandstone is a common building material. It's also common to see walls suffering serious sandstone decay - with a skeleton of cement pointing still hanging in mid-air around it. So yes, at least for the pointing, lime mortar would seem to be wise. I'd also think about blocking the uptake of ground water with a course of slate. However your sandstone may have completely different characteristics.
Initial thoughts: Lucky old you! (No stone in this neck of the woods so garden terracing has been put off and off...)
Then, there's sandstone and sandstone. Do you know what sort it is or where it came from (geologically). It must be fairly tough if it has lasted from mediaeval (nice to see the proper spelling) times, though shame the church had to go.
You might try a drop of acid on a piece of the stone and see if it fizzes. This would indicate a limy matrix is holding it together, and you might be able to 'weather' it with a mild acid spray to loosen some of the grains and then pressure wash them out (mind if it *is* very soft like the acidy stuff we do get round here, the pressure washer will drill right through it if you are not careful.). I'd go for the lime mortar if I was you: it lasted many hundreds of years in the church after all.
Mind you, if these blocks are two man jobbies and your wall is low, and your stone has nice flat faces, does it need mortar at all, other than as TNP hints, to soften the stress of any subsidence? You could leave gaps for plants, and/or drainage too.
That's the prime reason such walls are better built & pointed with lime. However lime is very slow setting, so you cant build far without waiting and waiting. Common solution is to add a tiny bit of cement,
5% at most, to help it go off enough to build further. There are better pozzolans to use though, cement isn't a good one.
I don't know the exact source; however, the church will have been in or around York. It was demolished in the 19th century and the window re-erected as a folly in a garden. It subsequently fell down and had to be removed.
Interesting ideas. I was going to have a go with the pressure washer and see if it made any impression. The stone really is quite soft.
Well, some are two-chap and others are one-chap. Not huge. The wall will abut a pavement along which children walk to school, so I wouldn't want anything falling off it!
I don't know the exact source; however, the church will have been in or around York. It was demolished in the 19th century and the window re-erected as a folly in a garden. It subsequently fell down and had to be removed.
Interesting ideas. I was going to have a go with the pressure washer and see if it made any impression. The stone really is quite soft.
Well, some are two-chap and others are one-chap. Not huge. The wall will abut a pavement along which children walk to school, so I wouldn't want anything falling off it!
Thanks Richard
Interesting that you say the stone is soft, as traditionally the 'York'stones would be expected to be fairly hard as cemented with silica, but it could vary from quarry to quarry, eg:
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