I had a 2 storey extension built on my house 22 years ago. It was built with 215 mm thermalite blocks rendered externally to finish. The render was sealed with a proprietary product and then coated with masonry paint. It was repainted seven years after. Over the years the old paint has been blistering and peeling off, leaving a poor sandy and friable surface. As a scaffold will be needed it is critical that the repairs are done correctly. I tried to repair it by grinding it back and filing with a render of cement, building sand, plastering sand but it will not adhere. Can you advise me please?
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