moisture content in pressure treated lumber

[jim gossage]

my front porch railing was recently rebuilt with pressure treated 2x4 and 2x2 southern yellow pine. moisture content is 19-32% in the wood. how low does the MC need to be before painting it? the southern pine website saws that MC should be no more than 19% for framing, but does not comment on painting. thanks

[Doug Mason]

When I rebuilt my fence, a quality paint store told me that, in general, new PS wood should be dried about 6 months before priming/painting.




my front porch railing was recently rebuilt with pressure treated 2x4 and 2x2 southern yellow pine. moisture content is 19-32% in the wood. how low does the MC need to be before painting it? the southern pine website saws that MC should be no more than 19% for framing, but does not comment on painting. thanks

[Cliff Rohrabacher]

Ya want it good and dry. Water in the wood will prevent paint from adhering. Some things like Catalyzing urethanes are actually assisted by some moisture content greater than what is good for paint.

Six months should be about right unless the environment where you are is very dry and warm. Then maybe sooner? Hard to say.

What I'd do is take a piece of the same material from the same lot and cut it to see if it's dry inside.
If you can't tell, put a chunk in a sealed mason jar and put that in an oven at about 250Deg F and see if it out-gases tons of moisture for a while. It's not accurate but it's a good way to see what's in the wood.

[John Callahan]

iirc Sherwin Williams recommends 15% MC or less. Check their website. One of their (or other brands) deck products might be a more suitable choice than paint. Waiting a period of time should lower the MC content enough for paint but I'd sand the surface before painting because of UV degradation to improve adheshion. Before coating I'd check for waterproofing- some PT treatments use paraffin as waterproofing which raises heck with paint/stain adhesion. A few drops of water sprinkled on the board will tell, water will bead up if has waterproofing and soak in if it does not. A bit after the fact but there is PT called KDAT (Kiln Dried After Treatment) that can be painted right away.