In article ,
ct writes:


I am trying to work out how to make up a Bath stone mortar mix to
build an extension. Various places sell ready mixed bags, but at
20-30GBP / 20kg bag that works out very expensive. Does anyone know
how I could mix my own? I am guessing that it is a mix of Bath stone
dust, some local-to-Bath sand, and white cement, but any suggestions
of particular combinations to try would be gratefully received!

You should only need it for the visible surface, not for the bulk
of the mortar (although you haven't said what you're doing with it).


I'm building an extension. I was going to build the inner leaf of the
cavity with standard blocks and mortar, and then the outer leaf with
reconstructed stone blocks and Bath-stone mix. Do you mean that I
should build the external walls with normal cement as well,

I don't know what's recommended for such stonework

and then just point the gaps afterwards with the Bath stone mortar?

That's a possibility.

Obviously this adds labour costs (or time overhead if you're
doing it yourself), and you need to contrast this with the
savings on mortar. If the sones are large, then they won't
use as much mortar as, say, bricks would.

How much gap would I leave for pointing if I did that?

About the same as the width of the mortar.

Another technique which is used is to blow brick dust of
the right colour (maybe mixed with cement, not sure) onto
the wet pointing. I guess this might not last so well.
I saw a brickie doing something like this when moving a
boiler flue. He drilled the new hole and saved some of
the brick dust. The old hole was filled with a dollop of
mortar and smoothed off. He then blew the saved brick
dust onto it, and finally recut what would have been the
mortar pointing through it. I can't see where this was
done now -- it's completely invisible on the wall.

--
Andrew Gabriel