Just finished investigating a blocked drain. When I took off the manhole cover I saw that bits of the lining had broken and fallen into the drain - one large bit was partly blocking the outlet, hence the problem. Anyway, all removed and running freely. But the wall of the manhole is cracked and peeling. In some places the brickwork is visible so I'd like to chip off any loose bits and re-render. What is the best type of render for this kind of job? It's on my property so not the water company's responsibility.