Porous materials, such as wood and plaster, take well to paint because their porous nature helps grab the paint and help it stick. But tiles have several factors working against them when it comes to painting.
Tiles used for interior applications, such as showers and bathtubs, are usually denser than other tiles. It is best to avoid painting areas that are frequently exposed to water altogether because over time the exposure to water can cause the paint to peel.
Also, the type of tile that you’re likely to want to paint are often subjected to a great deal of everyday abuse. For instance, foot traffic, soap scum build-up, or grease build-up.
Does this mean tile can’t be painted? No. But how long the newly decorated design will last would be questionable and the fact is that the painted tile will never look as good as replacement tile. The most vibrant and durable tile colours and designs are those that are incorporated during the firing process.