Retaining walls, Olney, MD
Retaining Wall Cleaning: Timber and Block
Timber walls and segmental block walls each need a different touch to come back to their original color without damaging the joints or the soil holding them up.
Chapter 01
Pressure treated pine walls that have gone black or green
A pressure treated pine retaining wall left alone for years does not just fade, it goes black and green with mold and algae working into the grain. One wall Kurt worked on had not been cleaned in over fifteen years, and it came back to its natural honey color once the growth was stripped off the surface. The wood underneath is usually fine. It is almost always a surface problem sitting on top of sound timber, not rot working through it.
Kurt sees this a lot on older properties around Olney and Bethesda, where a timber wall was built once and never touched again. If a wall on your property has gone dark and you are not sure whether it needs replacing or just cleaning, call 240-372-7267. In most cases it is the surface, not the structure, and a proper wash settles the question without guessing.
Timber retaining wall before and after cleaning, from black and green growth to its natural honey color
Segmental block walls and black mold
Segmental block walls hold onto mold differently than timber does. It settles into the texture of the block face and the mortar-free joints between courses, and it reads as a uniform dark stain across the whole wall rather than isolated streaks. One wall Kurt cleaned went, in his own words, "from BLACK mold infestation, to GOOD AS NEW," with the mold eliminated using earth friendly detergents rather than anything harsher.
The block itself is porous, so the cleaning has to actually lift what has worked into the surface rather than just rinse the top layer. Done right, the color comes back close to even across the whole wall instead of leaving patches where the mold was worst. It is the same earth friendly detergent approach used on decks and brick, just applied to a different surface.
Chapter 03
Washing without blasting the joints or the soil behind
A retaining wall is not just a decorative surface, it is holding soil back, so the wash has to respect that. Segmental block walls are usually dry-stacked, meaning the blocks are held in place by weight and interlock rather than mortar, and blasting straight into those joints at full pressure can work grit loose or push water where it should not go. The same care applies to timber walls: the goal is to lift what is growing on the surface, not drive water behind the wall and add pressure to ground that is already doing structural work.
That is why the pressure and the angle get adjusted wall to wall rather than run at one setting for every job. A wall in Silver Spring built from block gets treated differently than a timber wall in Gaithersburg, even though both come out the same way: clean, and still doing the job they were built for.
Kurt’s own words on one wall: "From BLACK mold infestation, to GOOD AS NEW." Mold eliminated with earth friendly detergents, the same way it comes off decks and brick.
Pressure treated pine, cleaned back to its natural color.
Segmental block, black mold lifted with earth friendly detergents.