If you want a cheaper solution, you can diy with Penten. Firstly, clean the slab throughly with water and let it dry. Then use a roller brush to apply Penten with few layers and let if dry completely between each layer. The leak should stop. I diy for my car porch. It will last few years.

Otherwise, you engage an Indon guy. It will cost about RM500 inclusive of fixing back plaster ceiling.

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