Concrete Block Repair
(Split-Face Block)

Chicago-area condominiums and other buildings made of concrete blocks frequently have issues that require block repair.

These concrete repairs can include the following:

  • Block replacement
  • Tuckpointing
  • Sealant application

“Concrete” Blocks Are Not All Alike

Discover the difference between CMUs, split blocks, cinderblocks, and Renaissance® Masonry Units.


Concrete masonry units (CMUs) are formed from a limestone and clay mix (called Portland cement) along with sand and stone. Although they are stronger than cement and come in various colors, they most often are gray, like cement sidewalks.

Additionally, CMUs can come in many sizes. They’re typically larger than traditional clay bricks. The face dimensions are usually 8” x 16”. Plus, they come in thicknesses of 4”, 6”, 8”, 10”, 12”, 14”, and 16”.

Besides different colors and sizes, CMUs come in many shapes and face treatments. Some even have the outward appearance of limestone or clay bricks.

Noteworthy, CMUs are more porous than bricks. Unfortunately, this means that once water enters a CMU, it can’t easily evaporate.

If CMUs are made with enough cement and the masonry units are appropriately waterproofed, they can withstand the Chicago weather. But many Chicago-Area CMUs and split blocks were never waterproofed correctly.

Split Block
(aka Split-Face Block or Rock-Faced Block)

Split blocks are also concrete masonry units. They have an aesthetically pleasing textured or chiseled front. Additionally, they tend to be less expensive than CMUs or clay bricks. As a result, Chicago builders used these blocks extensively from the mid-1990s to the mid-2000s.

However, their bumpy surface makes them more porous and absorbent than the smooth-faced CMUs. Therefore, they require proper flashing, drainage planes, and proper seal coating.

Cinder Blocks

Cinderblocks are made with a combination of concrete and coal cinders. They may be hollow or solid. Without the stone or sand of CMU blocks, they are lighter than concrete blocks.

As a result, they aren’t a strong building material; they are very porous and tend to crumble easily.

Renaissance® Masonry Units

Renaissance® Masonry Units (RMUs) are not concrete blocks at all. Instead, they are made of calcium silicate masonry units (CSMUs). Therefore, they have a high density and low absorption rate. These features help them withstand severe Chicago weather.

Unlike porous concrete-based products, these CSMUs, as a rule, should not be sealed or waterproofed.

However, they will become saturated if groundwater, moist topsoil, or melting snow or ice remain in contact with Renaissance® masonry units. Extensive moisture will cause stains and efflorescence (white powder formation). Furthermore, de-icing salts can cause spalling (chipping and splintering).

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Why Water Intrudes

A building’s water barriers can fail for many reasons. However, in our experience, the most frequent cause is construction that uses concrete blocks.

From the mid-1990s through the construction boom of the early to mid-2000s, Chicago builders favored concrete masonry units (CMUs) and concrete split blocks. (See ’Concrete’ Blocks Are Not All Alike.)

These CMUs and split blocks were less expensive. Plus, they shortened the time to build condominiums, homes, or other buildings.

However, concrete blocks are more porous than other masonry materials, such as clay bricks, limestone, granite, stone, or poured concrete. But if they contain adequate cement and are properly waterproofed, concrete blocks can withstand Chicago’s weather extremes.

Unfortunately, many of these turn-of-the-21st-century concrete buildings were not waterproofed correctly.

Watch for These Signs of Water Intrusion

If you own a condo or other building made from concrete blocks, watch for the following signs of water intrusion:

  • Water stains
  • Seepage
  • Puddles
  • Leaking
  • Dripping
  • Bubbling paint on ceilings and walls
  • Warping and buckling of hardwood floors
  • Dark mold
  • Musty odors
  • White powder formation (efflorescence) on exterior walls

When water seeps inside a building, it will run along a smooth surface that acts as a conduit. Some of the first areas impacted are where joists and beams enter the supporting exterior walls.

Therefore, common locations for these water problems might include:

  • Baseboards
  • Wooden window boards
  • Electrical sockets and junction boxes
  • Wall and ceiling corners
  • Inside closets, laundry rooms, and basements

Water can also enter cracks, structural defects, or improperly designed or installed joints.

How Gralak Masonry Fixes Concrete Block Problems

Replacing Concrete Blocks

If concrete blocks or split blocks are chipping or splintering (spalling), we’ll cut out and replace the damaged block with a new matching concrete block.


Like all masonry units, the mortar between concrete blocks may require tuckpointing. In addition, the mortar we use for concrete blocks contains added water sealant.

Learn more about tuckpointing.

Sealing Concrete Blocks

One of the most important repairs for concrete blocks is a sealant. Gralak Masonry specializes in the applications of siloxane waterproofing agents. This sealing agent infiltrates deep into concrete blocks and bonds chemically. In this way, it provides a superior barrier against rain, minimizing water exposure.

Split block masonry walls must be sealed
every 5 to 7 years.

Our Recommended Water Repellent

We prefer MasterProtect® (made by BASF) water repellent. MasterProtect  is a patented, high-performance, water-based repellent specifically formulated to protect the most challenging CMUs (Concrete Masonry Units). We prefer MasterProtect  because it:

  • Offers the highest degree of water repellency for concrete blocks.
  • Inhibits moisture intrusion.
  • Repels wind-driven rains.
  • Maintains the blocks’ outward texture.
  • Appears colorless.
  • Penetrates deeply into the block.
  • Resists mildew and fungus.
  • Safeguards blocks from freeze-thaw cycles.
  • Resists UV deterioration.
  • Shields concrete buildings from acid rains and waterborne chemicals.
  • Offers a low volatile organic compound (VOC), so it’s more breathable and environmentally friendly.

We apply the sealant according to the manufacturer’s recommendations and the block’s surface either using a:

  • Low-pressure electrical pump sprayer
  • Brush and roller

Seal Coating Application Conditions

  • Temperatures between 45 to 90 degrees Fahrenheit
  • 85% humidity maximum

Download MasterProtect Specifications (PDF) – MasterProtect  H 185, MasterProtect H 177.

“The greenest and the safest water repellent on the market.”

Chicago Building Code

The Chicago Building Code Chapter 13-120 -150. Exterior wall materials reads:

“Exterior walls constructed of concrete masonry units shall have flashing, weep holes, sealants, and caulking, which prevent the accumulation of water within the wall assembly and provide a means for draining water that enters the assembly to the exterior so as to prevent moisture from passing beyond the exterior wall cladding or veneer and entering the interior of the exterior wall.”

Cinder Block Repair

In addition to CMU and split block repairs, we offer block replacement, tuckpointing, and seal coating for cinder block structures.

Block Replacement

We will replace crumbling or damaged cinder blocks.


As with all masonry units, we can tuckpoint cinder block.

Seal Coating

We can also apply seal coating to cinder blocks. For this purpose, we use siloxane waterproofing agents. This seal coating penetrates deep into the cinder block and bonds chemically to provide a superior barrier against the elements and minimizes the block’s exposure to water damage.

Did You Know

Hairline cracks are often worse than large cracks. This is because the tiny cracks will draw water into the concrete split face block and trap it. Conversely, larger openings allow moisture to evaporate at the surface.


MasterProtect will not inhibit water penetration through unstable or cracked surfaces or surfaces with defective flashing, caulking, or structural waterproofing. Gralak Masonry Contractors use reasonable preventive considerations for the windows and iron or wooden decks around the buildings and for the neighbors’ adjacent buildings to complete the sealing process satisfactorily and successfully.

Moisture is the most common cause of premature (before five years) MasterProtect failure on masonry walls. Failure is generally due to elevated moisture levels that soften the exterior coatings.

Skillful Tuckpointing and Other Masonry Services

We’ll postpone a job if the wall temperature dips below 40 degrees or above 95 degrees Fahrenheit. At these temperatures, mortar won’t be at the proper consistency.

At optimal temperatures, we will only keep mortar for two hours; this ensures your mortar remains pliable.


The city of Chicago building code requires a permit to ensure the project meets minimum standards. These standards are intended to protect the integrity of the buildings.

Chicago’s Easy Permit Process Program is streamlined for small, simple home and building improvement projects.

Depending on your project and location, many different types of permits may be required. We often pull the permits. However, some municipalities require that the property owner obtain the permit.

If scaffolding is necessary and the Chicago Department of Transportation has approved the work, an Easy Permit can be obtained the same day.

We stand behind the quality of our craft. To that end, we offer the Gralak Guarantee.