We have a vintage earthenware bathtub which has chipped and spalled as a result of a long-neglected dripping faucet as well as hard use. We have tried to use the kind of porcelain patching products available in little jars from the hardware store. The eroded area is too large for these products to be effective. We have considered using swimming pool patching cement or trying to have a waterproof liner custom-made. We would like to know if anyone has tried these methods and found them effective. I am sure there are hundreds of similar tubs in the prewar apartment buildings of New York and many people would be very happy to have a lasting solution to this problem, since it is a real nightmare to get a huge old built-in tub out of a small apartment.