Hi, I need to repair some render at the bottom of my garage wall, it's not a lot so I just bought three 10kg buckets of sand and cement mortar mix, the kind you just add water to.As the reason I am doing it is that I am having problems with water ingress someone told me to get some sika sbr.My question is when using this as a bonding agent do I need to make up a slurry with cement or can I just paint it onto the wall then add some to the mortar mix and apply, thanks.