Sap is a tree's lifeblood; it carries the required nutrition from the roots out to the far ends of the branches and leaves. When wood is cut from the tree, the sap no longer runs as it did in the living wood. Lumber that has been kiln dried has had the sap heated to crystallization. From time to time, changes in humidity or temperature may cause cut boards to ooze sap. There are several ways to remove the sap.
Removing Fresh Sap
Fresh, oozing sap is a very sticky substance that can be difficult to remove. Use a thin metal scraper to remove as much of the sap as possible from the surface. Use oil soap to remove the sap residue. Apply the oil soap with a soft brush, undiluted, and scrub the surface well. Rinse the area with warm water to complete the removal process. Use acetone to remove any remaining residue from the wood.
Removing Hardened Sap
Allow the sap to set until it hardens completely so that the surface is dry and hard, without tackiness. Position a very sharp wood chisel with the bevel edge facing up, and the flat side of the blade against the face of the wood. Press the edge of the chisel under one edge of the sap until it pops loose from the stair surface. Use acetone to remove any residue from the surface.
Kilns crystallize sap in the wood by heating it up over 140 degrees Fahrenheit. You can use this same effect to your advantage with a handheld heat gun. Plug in a heat gun and set it on the highest setting. Aim the gun at the oozing area. Keep the gun moving to prevent scorching. Keep the gun focused on the area for at least five minutes, moving it slowly, allowing the wood to heat thoroughly. This may cause the sap to ooze initially, then harden. Remove any sap from the surface using a chisel and remove the residue with acetone. The interior sap will crystallize and harden into a rocklike deposit. Unless temperatures reach over 140 degrees Fahrenheit, you should not see oozing from this spot again.
Sand the wood surface with fine 220-grit sandpaper to smooth the grain and remove any crystallized sap. Sanding blocks help smooth large, flat areas. Use a Handheld oscillating, fitted with 240-grit sand paper, for edging and corners. Wipe the dust from the surface with a tack cloth. Apply a coat of stain and clear finish all-in-one or a coat of matching semigloss latex paint. Use a paintbrush to apply the matching finish smoothly. Allow the first coat of finish to dry completely. Apply a second coat, and a third coat if needed to match the original finish.
- Gardening Know How; How to Remove Tree Sap; Nikki Phipps
- "Mrs Fixit: Easy Home Repair"; Terry McGraw; 2001
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