@zoothorn, yes lime is best fir old stone buildings but as this is such a small area, in a porch and not covering the stone just go with 4:1 and a little plasticiser if you have any, it’s such a small area it’s not going to cause global warming/fall down. It sounds like your old barn was lime, it takes much longer to go off which is why you brushed it the next day. Using 4:1 sand cement will go off much faster so you need to brush it off after 1 or 2 hours with a fairly soft brush, it will still be wet enough to not be dusty but solid enough to not fall out/leave large marks. Crack on mate ?