When refinishing wood, it is sometimes necessary to remove the existing finish. Although seemingly a straight-forward process, tightly-bonded finishes or lead-containing paint can cause complications.
Scraping, sanding, wet or dry sandblasting, power washing, and using electrically heated pads, hot air guns and blowtorches are all methods to remove wood finishes—but do you know when to use which technique? Following are a few pointers.
Scraping is effective to remove loosely bonded paint or paint that has already partially peeled from small areas of the structure. If possible, sand weathered surfaces and feather edges of the paint still bonded to the wood. Do not sand if the old paint contains lead.
If paint has partially debonded on large areas of a structure, contractors usually remove the finish by power washing. This method works well for paint that is loosely bonded. If paint is tightly bonded, removal can be difficult without damaging the wood. The pressure needed to debond tightly bound paint from wood can easily cause deep erosion of the wood.
If high pressure is necessary to remove paint, the paint probably does not need to be removed prior to refinishing.
If more aggressive mechanical methods are required, wet sandblasting can remove even tightly-bonded paint. Dry sandblasting is not suitable for removing paint from wood because it severely erodes wood along with the paint and it tends to glaze the surface. As with sanding, power washing and sandblasting are not suitable for paint containing lead.
Some power sanding devices are suitable for removing paint that contains lead; they have attachments for containing the dust. Equipment that has a series of blades similar to a power hand-planer is less likely to “gum up” with paint than equipment that merely sands the surface.
Remember, if the wood has fasteners, planers and sanders cannot be used unless the fasteners are countersunk.
Finally, paint can be softened using electrically heated pads, hot air guns, or blow torches, and then removed by scraping. This process is slow, but causes little damage to the wood. Blowtorches can be extremely hazardous, particularly if the painted wood is on a structure, as the flame can easily ignite flammable materials beneath the exterior surface.
Heated pads, hot air guns, and blowtorches are also not suitable for paint containing lead. Lead fumes are released as a lead-painted surface is heated past 700 degrees Fahrenheit.
For more information, refer to Chapter 16 of the Forest Product Laboratory’s (FPL) Wood Handbook.