Following are some guidelines when using a moisture meter.
Decay and insects
Untreated wood that contains a moisture content of 20% to 60% is subject to attack by decay fungi. It’s not a matter of if it will decay but when it will decay. That’s why it’s so important that a finish on green wood be able to breathe in order to allow the internal moisture to escape from the wood rather than be trapped inside.
Non-breathable or vapor barrier finishes like oil-based alkyds state on their instructions: "Do not apply when moisture content of the wood is greater than 18%." When these types of finishes cover the surface of logs that contain a lot of moisture, the inside of the logs will begin to rot away and/or the finish will begin to peel off due to water vapor pressure.
Insects, too, prefer moist wood. Both carpenter ants and anobiid powderpost beetles typically infest wood members with moisture contents in excess of 30%.
Sealing or finishing logs
As we state in our literature, Perma-Chink products can be used on fairly green logs. But that does not mean that they can be applied when the surface of the wood is saturated with water. Even though the interior of the logs may contain 40% or more moisture content, the surface must be dry enough so that the sealant or finish adheres to the wood.
We would like to see the surface moisture content be 20% or less before applying any of our sealants or finishes. If the surface moisture content is too high, there is a chance that product adhesion will be compromised. This is also true after a home has been washed.
So how long do you have to wait for the wood to become dry enough to stain? It’s not so much a matter of time as it is surface moisture content. The objective is to allow enough time for the surface moisture to evaporate to a level of 20% or less. A moisture meter takes the guesswork out of the equation.
Moisture meters used to be high dollar items, but over the past few years they have dropped significantly in price. A quick search on eBay and Amazon.com produced a number of pin-type digital moisture meters for less than $25.00 plus shipping. For that price, a moisture meter is an excellent investment for both homeowners and professional applicators.