Paint Problems - Chalking

Chalking is a loose, white powdery pigment residue on the surface of a coating accompanied by a loss of sheen and color. This can be expected to occur over time and is a normal way for paint film to wear. In some cases, this is a self-cleaning feature designed into the coating. However, excessive film erosion can result from heavy chalking and result in the need for a premature repaint.

So now you know what chalking is...you may be asking "what causes chalking?"

According to the Master Painter's Institute (MPI), the main causes include:

1. Paint spread too thin, or thinned too much
2. Low quality or highly pigmented paint
3. Indoor paint used on an exterior substrate.

How do you fix this problem? Well, the first step is to remove as much of the residue as possible with a careful power washing. Check for remaining chalk by running your hand over the surface after it dries. If chalk is still present, apply a quality oil-based or acrylic latex primer. Repaint the surface with a high quality exterior paint. If little or no chalk remains and the old paint is sound, then priming may not be necessary.

For a technical evaluation of chalking, reference ASTM Method D659.