First of all, is this product any good?
http://www.wickes.co.uk/patch-repair-and-pointing-mortar/invt/222709/
And secondly would adding a little PVA to the mix be beneficial, to help the mortar bond?
http://www.wickes.co.uk/patch-repair-and-pointing-mortar/invt/222709/
And secondly would adding a little PVA to the mix be beneficial, to help the mortar bond?