Most species of wood can ooze sap or pitch for years after being cut, but wood from conifers such as white, ponderosa and southern pine is particularly prone to this sap-bleeding problem. Sap oozes mainly from knots in the wood. If you have a particularly “sappy” board as a stairstep, the sticky stuff can cover much of the board’s surface.
Cause of Problem
Cut lumber can have pockets of sap collected from an old injury to the tree. Sap also collects around knots. The knottier the wood, the greater the likelihood of bleeding sap. When weather warms, the heat of the sun draws the sap to the surface of the wood. This process will continue until all the sap has been bled out, which can take years or even decades. Drying lumber in a kiln to reduce warping or pressure-treating wood to make it rot-resistant cannot cure sap pockets.
What to Do
Hotter, drier weather will cause sap to bleed out more quickly, especially if your steps are exposed to the direct sun. You can treat lumber that has light to moderate sap bleeding problems. But if the problem is severe, your best course is to replace the bleeding steps with new stair wood. Choose fine-grained, knot-free deck lumber for the new stairsteps.
To treat bleeding sap, begin by thoroughly wetting the affected area with turpentine. If you can’t obtain turpentine, use mineral spirits sold as paint thinner. Scrub it into the sap with a coarse plastic scrubber to soften the sap. Scrape away the softened sap. Use a hair dryer or hot-air paint-stripping gun to heat the sappy area and draw more sap to the surface. Repeat the turpentine wetting and sap scraping. Sand the area smooth and spot-apply a good commercial exterior water sealer to sappy areas. You may have to repeat the treatment process next year if more sap oozes. Eventually, you will exhaust the sap from the board.
If your steps are inside the house and you plan on painting them, treat oozing knots with turpentine, heat and scraping, the same as for outdoor steps. After treating and sanding, seal the knots with two coats of white-pigmented shellac and coat the entire surface with a universal primer or sealer. After it dries, apply your finish paint.