Cement used by stonemason to bed new sandstone???

[Lithgae]

I've just found out that the stone mason working on my house (Sandstone/Whinstone rubble wall) has been using cement to bed the new sandstone, then NHL lime mortar for pointing.

I'm not particularly comfortable with this, but I the argument he is making is that rain only penetrates maybe an inch or so into the stone and so can still escape through the lime pointing. This of course presumes that there is no need for movement of water vapour from the inside to outside, and it also puts to the side the other argument for lime mortar which is flexibility.

My gut tells me this is wrong, but I am trying to be rational. Does anyone think that what he is doing is ok?

 

[malcolm]

One of my sandstone window sills was re-bedded in cement. I wouldn't mind so much but the fall is in the wrong direction. I don't fancy the chances of sandstone vs cement so I've bought a new sill ready for the new window. Stone is heavy enough not to blow away - it can go on lime to give half a chance of whatever adjustment might be needed in the future.

If it's a whole wall trying to behave in a breathable fashion it ought to be bedded in lime. Water moves through the mortar much more than the stone.

 

[Lithgae]

This is my feeling too Malcolm. What's disturbing about it is that I would have had no idea if I hadn't noticed the bag of cement. I suppose he didn't state at any point that he wouldn't use cement, but I think there is an expectation that if you are dealing with a stone mason rather than a regular builder, that they would be working with lime.

I feel a bit frustrated that I have just spent a fortune getting all the cement render off, only to find that the entire structure might not be riddled with the stuff!!!

 

[Gareth Hughes]

There are, at least theoretically, issues about the compatibility of lime mortar with sandstone (as opposed to limestone, which is chemically the same as lime mortar). Not sure of the details but although less damaging than cement pointing, lime mortar is not a perfect companion for sandstone.

 

[Lithgae]

compatibility of lime mortar with sandstone

Never heard anyone say this before. Lime mortar has been used here with sandstone for hundreds of years. Did a quick search and found a paper talking about this, although it didn't seem to offer any alternatives, and seemed to accept that cement wasn't an alternative as it brought with it a host of other problems.

 

[Lime]

I've just found out that the stone mason working on my house (Sandstone/Whinstone rubble wall) has been using cement to bed the new sandstone, then NHL lime mortar for pointing.

I'm not particularly comfortable with this, but I the argument he is making is that rain only penetrates maybe an inch or so into the stone and so can still escape through the lime pointing. This of course presumes that there is no need for movement of water vapour from the inside to outside, and it also puts to the side the other argument for lime mortar which is flexibility.

My gut tells me this is wrong, but I am trying to be rational. Does anyone think that what he is doing is ok?

My gut feeling is the same as yours.

 

[TheForge]

There’s potential for damage to sandstone from calcium salts being washed out of lime rich stone or mortar, for example sandstone courses under limestone masonry will often experience accelerated decay in comparison.

As a result it’s normally advised to use a natural hydraulic mortar for sandstone, which cointains less ‘free lime’ than non hydraulic mortars. There may be occasions when, to reflect the condition of the masonry however, non hydraulic lime may be more appropriate.