We don’t recommend it for several reasons. First, any bare concrete block, Ocala block included, absorbs water from rain. This type of block is less absorbent than modern concrete block, but the process of chemical stripping or blasting away the multiple coats of paint that have accumulated over the years will deteriorate the surface of the block, making it more porous. 

    Block is definitely forgiving of a little moisture intrusion. It doesn’t rot and ordinarily any water that is absorbed evaporates away. But when you combine the roughened surface with the inevitable settlement cracks and eroded mortar of an older block home—plus take away the moisture retardant paint coating—the block can easily become saturated beyond the surface in a driving rain. 

   Small cracks that meander down a wall in stair-step pattern, like in the photo above, are not as innocent as they look. A crack only 1/32” wide (less than the thickness of a dime) and three feet long is equivalent to a one-and-a-quarter inch diameter hole drilled in wall for water intrusion. Paint easily spans and seals these hairline cracks.

    And stripping paint off a wall with inset grout joints is neither easy or cheap. If you do decide to try to reclaim the mid-century block surface, we recommend applying and maintaining a clear sealer recommended by your painting contractor to protect the surface against moisture intrusion when you’re done.

    Why was bare Ocala block not a problem when it was so popular with Florida architects in the mid-20th century? Homes weren’t air conditioned back then, with windows open for ventilation during the hot and humid months, so there wasn’t the temperature and humidity differential between outside and inside that induces moisture migration, and the surface had not yet been roughed up by years of weather eposure and settlement.

    Also see our blog posts What is "Ocala" block? and How can I tell when it's time to paint the house?

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To learn more about exterior walls and structures, see these other blog posts:

• What is the average lifespan of a house foundation?

• What causes vertical cracks in fiber cement siding planks?

• What causes raised white lines of residue on a block wall that are crusty and crumbling? 

• What is the difference between soil subsidence, heave, creep, and settlement? 

• How much ventilation is required for the under-floor crawl space of a home? 

• What causes stair-step cracks in a block or brick wall?

• What causes a horizontal crack in a block or brick wall? 

• How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

• What causes the surface of old bricks to erode away into sandy powder? 

• What are the pros and cons of concrete block versus wood frame construction?

• Should I buy a house with a crawl space? 

• Why is my stucco cracking?

• There's cracks running along the home's concrete tie beam. What's wrong? 

• What would cause long horizontal lines of brick mortar to fall out?

• How do I recognize serious structural problems in a house?

• What is engineered wood siding?

• Should I buy a house that has had foundation repair? 

• What is a "continuous load path”?

• Should I buy a house with asbestos siding?   

• How can I tell if cracks in the garage floor are a problem or not? 

• What do you look for when inspecting vinyl siding?

• Why is housewrap installed on exterior walls under the siding? 

• Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

• How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

• Should I buy a house with structural problems? 

• What are those powdery white areas on my brick walls?

• What causes cracks in the walls and floors of a house?

• How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

• What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck? 

• How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

        Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.