The Importance of Understanding Moisture Content: Before You Paint Wood

Wood is a very absorbent material. New lumber, for example, can have a moisture content in the range from 12% to 25%. There are many factors that can contribute to this:

· The type of wood

· The climate where the wood is from

· The time of year

· And the time since the building was constructed

It’s very important to test the moisture content of wood before painting, especially new construction and wood siding. Even if wood feels dry to the touch it can still have a high moisture content. Using a hand-held moisture meter is easy and accurate. Try and get the prongs of the meter at least 3/16 of an inch into the wood. You are looking for a moisture content of less than 16%.

It’s obvious the exterior wood is exposed to environmental moisture like rain and dew. We need to monitor the weather when planning exterior painting. However, it is the moisture that penetrates the wood from the inside that can really destroy an exterior paint job. 

Homes that were built be the use of vapour barrier can often experience moisture problems on the warm side of the exterior walls. Frost can form on the inside of the wall cavity from the warm moist air inside the house. When this frost melts as the weather improves the resulting moisture can be absorbed by the wood and penetrate the siding. If your homes paint job doesn’t last more than a couple of years you may be experiencing this problem. The underlying problem must be repaired first before it makes any sense to paint.

Anytime you are painting interiors the same cautions will apply. Especially when a restoration has been completed after a flood or fire where there has been water damage. Sometimes when the contractor is under pressure to get the job finished to meet a dead-line they may not leave enough drying time before the drywall goes on. When you paint the drywall may feel or appear dry, but that moisture will eventually reach the surface and cause your paint to fail.

Again, your moisture meter will be useful in this situation. Ideally you would check the framing for moisture before the drywall is installed, however, if you can’t you should wait as long as possible and then test the drywall. 

Delivering a professional painting job is not just about skill with a brush, roller or sprayer. It’s also about understanding the finer details like understanding moisture.