Anyone who has enjoyed maple syrup on pancakes can tell you tree sap is inherently sticky, but if you left your painted lawn chairs near the treeline or parked your car under a redwood tree during a windstorm, you already know that. It isn't just redwood and maple trees that exude sticky sap -- virtually all trees are capable of that -- and the sun can bake the sap into hard crystals that can be almost impossible to scrape off. In fact, the best approach isn't to try to scrape them, but to dissolve or lubricate the sap away, and a number of solvents and oils can do the job.
Dissolving Tree Sap Resins
Resins from the sap of pine and other trees have long served as wood finishes. For as long as people have used them, they've also used turpentine, which is distilled from oils from the same trees, to dissolve these resins. Mineral spirits is the modern version of turpentine, and it's a natural remedy for tree sap spots on glass. It's also an appropriate solvent for removing sap from painted wood, because it isn't strong enough to harm a cured paint finish.
Removing Tree Sap with Mineral Spirits
Moisten a rag with mineral spirits so that the rag feels wet to the touch without being dripping wet.
Use the rag to pinch the tree sap spots off of glass or painted wood. Avoid rubbing, which can spread a thin film of sap over a wider area.
Let the rag rest on larger sap deposits for a minute or two to give the solvent time to dissolve the resin, and then remove the resin with a pinching motion.
Scrape stubborn deposits with a plastic paint scraper after soaking them with mineral spirits. Once most of the resin is gone, use the solvent-soaked rag to wipe off residue.
Alternative Removal Methods
You may need a stronger solvent to remove some types of tree sap, but if you're removing sap from a painted surface, you you don't want to use a solvent that damages the paint. Nail polish remover that contains acetone is always safe to use on glass, and it's safe for most finishes, but you should test it first.
Similarly, isopropyl alcohol quickly removes sap from glass and is safe for oil finishes, but avoid using it to remove sap from a surface painted with latex paint, because it will affect the color of the paint.
Loosen the Sap With Oil
If you're squeamish about allowing any type of solvent to come in contact with a painted surface, you can use oil to loosen the grip of the sap to the surface to which it's adhering. Put a few drops of olive oil on the sap, or cover the sap with mayonnaise -- which contains olive oil -- or peanut butter, which contains peanut oil. Wash off the oil or condiment -- and the sap with it -- after a few hours. A similar strategy is to pour oil soap onto the sap deposit, wait 15 minutes, then scrub and rinse with water.