Why has the painted surface become mottled?

The mottled appearance does not indicate a problem. It can usually be seen after the second coat on a new wooden surface and is due to the wood having absorbed the paint unevenly. If the mottled appearance occurs after the final coat, it may be because the underlying paint layers have not dried or cured enough. It can also be due to the color being unevenly applied. The easiest way to fix mottled surfaces is to let the paint dry and then apply a new coat of paint. Some mottling will disappear on its own over time. Adding 1 percent desiccant to the paint reduces the risk of mottling.