Sticky sap situation
I recently built picnic tables out of rough-sawn pine that had been air-dried outside for about 8 years. But sap constantly bleeds out around the knots, making it impossible to sit in certain spots.
Do you have any suggestions?
—Darrell Verheyen, Ashwaubenon, Wis.
Unfortunately, Darrell, pitch bleeding often occurs in pine that has been air-dried—even years after cutting. The process of "setting the pitch" in sap-soaked wood relies on heat rather than time. Heat the wood enough, and the pitch will "volatilize," either evaporating or crystallizing. That's why kiln operators often heat pine to around 160° F.
In your situation, given time and enough seasonal temperature highs, the pitch bleeding will eventually run its course. In the meantime, remove the sap with a scraper and sand away any hard residue. Then, apply a coat of a de-waxed shellac sealer, such as Zinsser SealCoat Sanding Sealer (zinsser.com, 732-469-8100), trapping the sap under the surface. If some pitch still bleeds through, remove the sap again, and apply another coat of sealer to the trouble spot.