More on the Chicago Split Faced Block problem.

This was an older (circa 1920s) apartment to condo conversion building. They had built it out in the rear, adding extra space. The original building was the typical 3 wythe brick with clay coping tiles, but some tiles were missing and the damaged tiles were not replaced, but merely covered with plastic roof cement (also called roof dope, because only roofers who are dopes use it). Common defect around here.

The split block was also covered with clat coping tiles, which is OK, but the condo board was concerned about water intrusion. They decided to cover the exterior split block with furring strips and vinyl siding. BUT…, they did not change out the coping tiles with wide ones, but only sealed the parapet top with… Wait for it! Ta Da! CAULK!!!

The proplen is not so much the exterior absorbing water, but water entering the wall from the top, through the parapet coping. I keep telling people this, but there are many “masonry sealing” companies and siding contractors who fast talk the owners into believing that the water is coming through the side of the walls, through minor mortar cracks.

First rule of masonry in Chicago: Never build a single wythe masonry wall!

You can’t cure stupid.

(Hat tip to John Olsen)

First time I have seen them put siding over that .
Did they have a moisture resistant barrier under it?

At least the porch looks good…5 bolt splices which are required but rare unless right near the lakefront.

  1. There were no porch pictures, so I don’t know what you are talking about.

  2. They put 1/2" foam board “insulation” underneath.

  3. The point is that very little water is absorbed through the block (horizontally) but enters the wall from the top because of lack of flashing.

Hope this helps;

I see the porch in the background unless that is the next property.
Think siding was a better option than sealant?
Minus the coping issue.

Acording to my research and experiments, 75 - 80% of the water entering the masonry of the wall comes from above. Sealing helps, but flashing gives more bang for the buck and stops more water entry. It’s a balancing act.

My uncle tried to buy a condo in Chicago a while back and the inspector said that very same thing, that water damage inside was coming from moisture penetrating the block.

If what you say is correct then in the future will check the top floor the closest.

Amazing how often when inspecting split block units I check under the spa tub and see no insulation to get a full interior view of the exterior wall covering.
Always those 2 inch ferring strips to hang the drywall on as well.

My main comment to clients is to make sure a study was done on the split block.
Unfortunatly despite all my concern they often proceed.

Not sure if this is yours but this is my standard statement .

[SPLIT BLOCK]](Split faced block )is a very porous material, so if not properly installed
and maintained, it tends to lead to costly repairs. The durability of split
faced block often causes the homeowner to over look the preventative
maintenance needed to help prevent the block from absorbing water
block is also important. Due to the permeability of the block and poor
water to exit from behind the block, damage to the interior can often

Like all exterior finishes, proper installation and maintenance are
needed. Split faced block is an attractive, long lasting finish that given
preventative maintenance and proper installation can last for many
years. I recommend that a proper water repellent is applied

You might want to proof read that again, Bob.

  1. The best solution is to not build a single wythe masonry wall, especially in Chicago.

  2. If it is already built, here are the necessary details:

  • Small exterior cracks should be sealed using Vulcum caulk.
  • Seal exterior with a polyurethane, “plugger” type paint applied according to the manufacturer’s specifications (flood coat).
  • Make sure that the parapet walls are properly flashed at the coping. Through wall flashing (IPCO) is stainless steel drip edges.
  • Make sure that all joist pockets are properly through-wall flashed with weep wicks.
  • The joists flashing should extend out from the block, again stainless steel drip edges are preferred.
  • Interior furring strips should not be in direct contact with the masonry. Never have wood in contact with masonry, HI # 101.
  • On the interior, insulation should be closed cell spray foam.
  • The underside of the roof decking plywood should be coated with open cell spray foam as a vapor barrier and as insulation.

Here’s my verbiage:

If the place looks OK (no water intrusion detected):

“While not properly installed or equipped with the properly installed and required joist pocket flashing, the split faced block is properly sealed and water intrusion was not present through the masonry at the time of the inspection. Recommend that the block be evaluated and, as needed, properly and professionally sealed, either with a penetrating sealer on a 5 year schedule or with elastomeric paint as a guard against water intrusion through the block. Recommend that the work be done by a licensed and insured masonry contractor with experience with split block maintenance and that a regular maintenance schedule be established.”

If not OK:

“Recommend that the exterior wall split faced CMU be sealed against water intrusion. The current best product for this is an elastomeric plugger type paint. Recommend that the repair and sealing work be done by a licensed and insured masonry contractor with specific experience dealing with split faced concrete block issues.”

Also make sure that the coping is properly flashed and that they did not take the roof membrane up-and-over the parapet wall. This makes the interior portion of the parapet wall “inside”, i.e., compromising the building envelope.

I have a guy who I have been working with who developed a breathable coping, as well as a breathable termination bar. But as you know, flat roof roofers around here never learned about counter flashing above the ternination bar.

And, if the roof is sloped (i.e., no parapet wall), there is usually no problem.

See this article for more information:

Hope this helps;

Looks great and will go through the comments in detail to cherry pick.
Bear in mind joist pockets and most of the structure is hidden from view during a typical split block building condo unit inspection.

The detail here is better than my typical unit inspection comments would require but fantastic information none the less.

Does the Plugger type paint you recommend during your full building review contain a silicon base at all?
You mention poltyurethane however as far as I know that does not have penetrating properties.

Normally I recommend a urethane based caulk at pipe penetration points as it has a better stick(adhesion) property to masonry than silicone.

Hope this helps;