I need a coating/paint suitable for external masonry that is capable of withstanding extreme heat and will protect the render from cracking. Is there anything you can suggest? The render is already cracked so if there is anything that will avoid the area needing to be re-rendered, that would be a bonus.
We're able to offer a waterproofing, flexible and crack bridging product in way of Rust-Oleum Mathys Murfill Waterproofing Coating. This can be applied to old, sound paintwork following thorough brushing down. If the surface is bare or the paint surface is chalking, you wuold need to first prime the surafce with Mathys Pegafix. Any cracks larger than 0.5mm would need filling with Rust-Oleum Mathys Elastofill. The system will not necessarily prevent further cracks in the substrate but the flexibility in the coating will prevent cracks from showing.