Pressure washing costs in Knoxville

Old North Knoxville's design guidelines put it in four words: never waterblast masonry surfaces. The guidelines, adopted by the city in 2003, explain why. Blasting with any material, water included, strips the hard outer layer that brick gets in the kiln and stone gets from weathering. That leaves the wall open to the freeze-thaw cycles the guidelines call so prevalent in Knoxville's climate. A thorough soak from a water blaster can also wash out so much mortar that the whole feature needs repointing.

For a grimy brick wall, the guidelines suggest something much gentler. Use a soft bristle brush with gentle soap and water, and rinse at no more pressure than an ordinary faucet. Try any method on a test patch of at least two square feet, then let it weather before you judge it.

The Fourth and Gill guidelines add a reason to clean less often. They say to clean masonry only to stop deterioration or to remove paint or heavy soiling from pollution, because cleaning can put needless moisture and chemicals into the building. They also ask owners to leave patinas alone.

Old wood siding gets the same answer when it's time to strip paint. Water blasting, sandblasting and propane or butane torches are all out, because they can damage historic wood. Old North Knoxville's guidelines point to hand scraping or hand sanding instead, and only down to the next sound layer of paint.