How to protect stone masonry wall from weather
I visited my local paint shop and got a handful of paint cards to match against the current paint. I selected the paint and had it mixed up to good quality. It is a dark grey which is common in my area. I brushed off any loose sand from the stone before painting. Areas that were falling off in lumps I put PVA glue mixed with a small amount of water on it. 

You can then paint over that area if need to. I will have to keep on top of painting the lower part of the wall. It will protect against rain and wind. 

The problem was the stone was going soft and flaking off. I wanted to know how to protect the stone from the weather. This seems to work. It is worth paying for the paint because it is very expensive to have to outer wall rebuilt. The wall was down the side of the house with a walkway so you do not see it. It was the bottom that got the worst of it.