Hello, I have a porch with mortar over brick walls. The mortar began cracking and moisture got behind it causing it to get soft in some areas and it is now falling off. Behind it is sand but the outter part is hard. Can I just get rid of the loose parts that are easy to remove and repair those areas with new mortar. What kind should I use - is Type N ok? How do I apply it and make it stick to the wall? What consistency should it be? Thanks for any help.