Concrete blocks (CMUs) only need to be filled if they serve a load-bearing purpose, require steel reinforcement for lateral strength (like wind or seismic resistance), or are used in retaining walls. Unfilled blocks can support typical non-load-bearing walls and offer better thermal insulation.
Seven common mistakes when installing retaining wall blocks include poor base preparation, inadequate drainage, not using proper backfill, failing to compact soil, improper alignment of blocks, ignoring wall height limits, and neglecting to use geogrid reinforcement when needed.
The 90-minute rule for concrete is an industry-standard guideline stating that ready-mixed concrete should be completely discharged from the mixing truck within 90 minutes after water and cement first combine.
Fill the cores with mortar, making sure that the bolts extend a few inches above the top of the wall. Use QUIKRETE® Masonry Coating to waterproof both above and below the grade line.
Should concrete blocks be filled in every project: Not always. You should fill blocks when you need more strength, like in tall walls, basement walls, or walls that hold up heavy things (load-bearing walls). But for short walls inside your home that don't hold weight, you can leave them hollow and save money.
Coca-Cola does three main things to concrete: it slows down the curing process (acts as a retarder), etches the surface to expose decorative aggregate, and removes tough stains. This happens because of the soda's high sugar content and phosphoric acid.
Water is the most common enemy of concrete surfaces. When water penetrates the surface of concrete, it can cause it to crack and weaken. This is especially true in colder climates where water can freeze and expand, creating even more damage.
Neither mortar type is universally "better"; their suitability depends entirely on the application. Type S is superior for strength, underground use, and load-bearing applications, while Type N is better for general use above-ground, offering easier workability and flexibility.
Coverage - Each 80 lb (36.2 kg) bag of QUIKRETE Core-Fill Grout – Coarse will fill the cores of approximately 3 standard 8 in x 8 in x 16 in (200 mm x 200 mm x 405 mm) blocks.
A 2-inch concrete pour takes 24 to 48 hours for foot traffic, 7 days for light vehicle traffic, and 28 days to achieve its full design strength. Although thin, concrete relies on chemical hydration to gain strength, meaning the curing timeline is identical to thicker slabs.
A standard 20x20 concrete slab costs between $2,400 and $4,800 fully installed (about $6 to $12 per square foot). For reinforced, thicker, or decorative slabs (like stamped concrete or those needing extensive site prep), the cost can range from $5,000 to $11,000+.
If it rains 12 hours after your pour, your concrete is almost certainly safe. By this point, the concrete has largely hardened, and rain will generally not impact its structural integrity or wash away the surface. In fact, the added moisture can even act as a free "wet cure".
Yes, you should fill hollow retaining wall blocks. Filling the block cavities and the space behind them with 1/2-inch to 3/4-inch crushed, angular gravel significantly increases the wall's weight, knits the blocks together, and ensures proper drainage to prevent water pressure from pushing the wall over.
Yes, you should fill hollow retaining wall blocks with gravel. This process is known as core filling.
Retaining walls usually fail because of poor or improper drainage, leading to a dangerous buildup of trapped water pressure. When water pools behind a wall, it adds heavy hydrostatic pressure that the structure isn't designed to hold. Other major culprits include underestimating soil weight, poor installation practices, and misjudged load calculations.
If the conditions are right, concrete building blocks have a lifespan of 100 years or more. This makes them a very durable building material. Indeed, concrete created during the Roman Empire can still be found today, which demonstrates how long-lasting it can be.
Mixing concrete yourself can be the cheaper choice for small projects. For larger jobs like driveways, slabs, or patios, delivery often wins. Hand-mixing takes much longer, and mistakes in mixing water or cement can weaken the final product. One cubic yard of concrete requires about 45 bags of 80-pound Quikrete.
For masonry cores over 4 inches wide, QUIKRETE Core Fill Grout – Coarse should be poured around the rebar; for masonry cores under 4 inches wide, QUIKRETE Core Fill Grout-Fine should be used.
The terms “masonry block” and “concrete block” are often used interchangeably, and for good reason. Both refer to the same fundamental building product – the CMU.
Dirty or Messy Surfaces
If the surface is dirty, mortar won't stick well. Dust, grease, or dirt can weaken the bond. Clean the surface fully before adding mortar. Cleaning also makes the surface rougher, which helps it stick better.
Type S masonry mortars are used for building structural masonry walls above or below grade. Limitations: Masonry mortars must be blended with a specified amount of properly graded sand meeting ASTM C 144. For stucco applications use sand graded to comply with C 897.
Dish soap is full of unknowns—fragrances, dyes, surfactants—not designed for cement chemistry. These can interfere with other admixtures, delay setting times, or even cause efflorescence and discoloration.
Because vinegar is mildly acidic (acetic acid), it reacts with the alkaline components in concrete. It can safely clean dirt or lift light stains when heavily diluted and quickly rinsed, but applying it at full strength or letting it sit will damage, etch, or degrade the concrete surface over time.
No Space for Storage or Utility Lines. Another significant downside to owning a home on a concrete slab is that you'll be missing out on the functional space that a full basement (and even a crawl space) can provide.