Painting Contractors: Ventilation is Good for You and Your Paint

When applying paints on interior surfaces it is important to consider the ventilation or airflow in and out of the room.

Solvent based paints can pose a safety and health hazard if there is little or no ventilation during the application. People with allergies can be subjected to health related responses ranging from mild asthma to severe headaches over a relatively short period. This can even come about when using paints containing the weaker hydrocarbon solvents like stoddard solvent and mineral spirits which are found in most interior alkyds. Low odor solvents like the paraffinic napthas can be particularly dangerous as they are difficult to smell even at relatively high concentrations.

Depending on the type of coating being applied, the solvent based materials can pose more significant fire dangers. Lacquers contain solvents that are capable of igniting at temperatures as low as -7° C if exposed to an open flame or spark in a concentration between the LEL (lower explosive limit) and UEL (upper explosive limit). Ventilation is a method of keeping the concentration below the LEL.

Latex paints are less dangerous but also should be well ventilated. The average latex paint can contain a concentration of 60 - 70 percent by volume of water. Now, let's assume that it will take five gallons of paint to coat the interior walls of a room once and that the latex paint used has a volume solids of 40 percent. When the painting is completed, there will be three gallons of water that has evaporated into the air. This is a significant rise in humidity in the air and can hinder the proper curing of the paint.

Most general purpose latex paints contain a co-solvent. This is a powerful, slow evaporating solvent like Butyl Carbitol (diethylene glycol monobutyl ether) that assists in fusing the emulsion particles together after most of the water has evaporated, to form a cohesive film.

Where the evaporation rate of water is affected by the humidity level (high humidity = slower evaporation rate), the co-solvents are less affected and tend to evaporate at a constant rate. So, in a high humidity situation, most of the co-solvent is leaving the film before the water. This can leave the paint film poorly fused (coalesced) and create problems such as poor adhesion, water resistance, low film integrity and gloss and color variations when the water has finally evaporated from the film.

To maximize safety and the film forming properties of a paint application on an interior surface, a moderate air flow can be the least expensive tool.