The interior of my stone basement foundation wall has been mortared it is starting to sand off. What is the best way to seal it off so I can paint it again? The home was built in the 20's and has no water problems.
If the mortar is crumbling and flaking, it MUST be removed. It is a tedious job, bit to assure a good solid surface, you have to remove all loose mortar, key it, and point all the joints. Let it cure a few weeks, be absolutely it is dried, then go for the finish. If you don't get to a solid base, you will be wasting your time and paint. Remember, the right way is the only way.