CAN’T RECOAT

Q. I am a manufacturing engineer at our plant. We make parts for small household appliances and, as you know, their appearance is very important. No matter how carefully we handle our painted parts there is always some damage due to rough handling.

As you know, stripping and recoating is very costly in terms of time and labor. We are now applying a new baking enamel coating that is very durable. We tried touch-up and recoating by spot repair and total recoating with a durable air-dry paint, but we can’t get the touch-up paint to adhere to the damaged parts. I’ve never seen anything like it.
Is recoating products a common problem? What can we do about it? R. B.

 

A. To answer your first question, recoatability is not a common problem. Although rare, I have seen this problem with highly mar-resistant finishes of the type you are applying. This is the case when a slip agent is formulated into the paint to increase its abrasion and mar resistance. These slip agents are waxes, polymers or other incompatible substances that come to the surface as the part is coated. Painting over these surfaces is almost like painting over mold release; the second coat of paint will not adhere. They act as an interference coating.

Your second question is not as easy to answer. In some cases, the slip agent on the surface can be removed by sanding. In others the slip agent can be removed by solvent wiping. If these attempts fail, ask your paint supplier to reformulate your baking enamel using less slip agent or a different one. There are classes of slip agents that are recoatable.