The houses on my 1990 housing estate where built using calcium silicate house bricks. These bricks did not have a frog and all sided of the brick were flat. Over the years all of the houses have suffered from some cracking of the mortar. Different surveyors called in have suggested a lack of ties, trees and bushes to close to houses and the wrong type of mortar mix. It is nothing too serious and a good eye is needed to spot the cracks.
I am now about to have an extension built and have managed to find some of these bricks but with frogs, as they are the only ones I could find that match. The instructions that came with the bricks state that the mortar mix should be either 1:1:6 or 1:2:9 for Cement : Lime : Sand. Do I need to insist that the builder adds lime as I have read the following post on another thread here about cement?
Re adding lime to cement mortars, this doesn't give any of the properties of a lime mortar. Also most lime/cement mixes are liable to fail prematurely, so adding a bit of lime to cement mortar or adding a bit of cement to lime mortar are both not recommended. There has been research done on this.