Making Concrete Block at Nitterhouse Masonry
The process of making a concrete masonry unit (CMU) hasn’t changed much since its inception in the early 1900’s. Raw materials are mixed with water, formed into a mold and left to cure for a period of time. The basic process is simple, but with advancements in the industry over the years, CMU manufacturing has become a science of chemical engineering and architectural integrity.
From our beginnings in 1923 as Nitterhouse Concrete Products to the family of concrete and stone companies that is Nitterhouse today, we’ve created better systems for increased production, quality control, process monitoring and a vast array of architectural concrete products. Our CMU process uses the best of technology and equipment, managed and monitored by a dedicated team that takes pride in every block we produce.
We offer a wide selection of visual effects and produce certain designs that provide specific structural features for unique applications. You’ll find the aesthetically pleasing natural beauty of stone showing through in different ways depending on the type of block. Additionally, the recycled material in our Recycled CMU may be just what is needed for your next environmentally-focused build.
While you have plenty of choice in the look of architectural block, the basic process of making concrete block is the same. There will be variations in the type and amount of raw material as well as the curing time, and environment will be adjusted depending on the qualities needed for the finished product. We provide our CMU block process to help architects realize our production capabilities, to assist engineers in picking out block that is structurally stable for their design and to enable masonry contractors to know what can be produced quickly when needed.
There are generally just two types of materials needed to form concrete block: aggregates and cements. The aggregates such as sand and crushed stone form the main structure of the block. The cement acts as the binder that holds the aggregates together and solidifies the block when it’s mixed with water.
The sand, stone and cement are delivered to our plants in large-volume dump trucks from local quarries. The aggregates are stored in open air storage bins in our yard. Since the cement is sensitive to moisture, it is blown into our cement silos. We have various types and sizes of aggregates and cements to produce our diverse line of architectural concrete block.
Every concrete block unit will contain the following materials in different quantities and variations depending on which type of architectural block we’re running on the production line:
The Manufacturing Process
In comparison to concrete mixtures used for general construction purposes, a concrete block mixture will have a higher ratio of sand to gravel and water. This produces a dry, stiff mixture with high compressive strength that holds its shape when it is removed from the block mold.
The materials that are needed for the day are scooped up in the yard by a front-end loader and dumped to enclosed compartments connected to the production line. Our machine operator selects the amount of raw materials needed for the batch being produced on our computerized system, which precisely measures and releases the material to make the type of block we’re running.
Here’s how the process goes:
After the appropriate amount of materials are measured, they are dumped onto a conveyor belt. The conveyor moves the materials to our 1.75 cubic yard mixer where water is added as the aggregates and concrete are poured in. The water is also precisely controlled with our electronic measuring system to ensure the mixture is not too wet or too dry.
Any additional admixtures like water repellents or pigment are then added, and the batch is mixed for six to eight minutes.
When the mixture is adequately combined, the concrete is moved on to another conveyor belt to be taken to our block machine. One of our various molds will be set up for the specific type of CMU we’re producing with the batch. After the batch is poured into the molds, the block machine compacts the concrete mixture by vibration. We do this to give the concrete strength and consolidate the concrete into a block.
Molding the concrete is the most important step in making CMU. Proper compression is essential to a quality finished product. The materials are fed into the molds at a measured flow rate, and the vibration time and force is accurately controlled to result in the appropriate height and strength of the block.
When proper compression and consolidation are achieved, the block is pushed out of the mold onto a steel pallet so it can be transported to our kiln to be cured. At his stage, the cement is called “green block” before it has cured and hardened.
The pallets are then moved to carts which travel into our low-pressure steam kiln to be heated. Generally, the rack of concrete block is preset in the kiln at normal humidity and temperatures (70 to 100 degrees Fahrenheit) for up to three hours. Then the steam is gradually introduced to the kiln, and the temperature is slowly increased to the appropriate level.
When the top temperature is reached, the steam and heat are shut off, and the blocks cure for another 12 to 18 hours in the hot, moist air. Then the moist air is exhausted out of the kiln, and the temperature is raised to completely dry the block.
A block typically cures for 16-24 hours at high humidity and an average temperature of approximately 100 degrees Fahrenheit.
- Cubing and Storing
When curing is complete, the concrete masonry block is rolled out of the kiln. Each block is then unstacked and placed on our conveyor. They move on to our cubing system which stacks the blocks on a wood pallet. Each block is aligned and stacked to form a cube four blocks across by two blocks deep and six blocks high.
Our split-face blocks, for example, are molded with two blocks joined together. Once they are cured, the double blocks go through our splitter. The splitter strikes the joined blocks, causing them to fracture and create a rough textured look on one side of each piece. They are then cubed and stacked.
We wrap the cube in plastic for security and protection from the elements, and it is taken by forklift to be placed in the appropriate section of our yard for that specific type of block or for a specific order. From here, block trucks will come and load the product as needed.
Quality Assurance in Our CMU manufacturing
The various sections of our plant are monitored constantly to confirm we are producing block with specific features. Whether it be the strength, weather and chemical resistance or design specifications, we have electronic monitoring and machine operators constantly making certain the finished block will perform as required. We ensure:
- The aggregates and cement are electronically weighed to be sure proper portions of each material, which affects the look, feel and durability of the block, are correct.
- The moisture content in the sand and gravel are measured with ultrasonic sensors so the exact amount of water can be added to the mixture for the precise water content needed for the batch.
- The size and density of each block is checked with laser beam sensors as each block exits the block machine.
- The curing environment is regulated electronically to control cycle times, temperature and pressure. All information is recorded for every batch.
- The finished blocks are tested for various qualities like sound transmission, water penetration, fire resistance, strength and shrinkage.
Concrete block is depended on to withstand severe weather, fire and other forms of serious damage. There is nothing better to build with than block when you want a building material that is durable, fire-retardant, insect-resistant and intrusion-proof. We make sure that integrity remains in every block that leaves our plant.
The Many Faces of Architectural Concrete Block
At Nitterhouse Masonry Products, we take pride in every single block, paver and stone we produce. We always make sure all of our products are manufactured to the highest standards and the best possible quality. Our line of architectural concrete block includes a variety of options with textured looks or smooth veneer finishes and various colors, shapes and sizes to provide design professionals with a wide range of options in concrete masonry construction.
Whether you need the basic concrete block for a rush job, have an architectural specialty to build or need a specific look for an elaborate office building, we can produce the block you need. Get familiar with each concrete block unit to know all that’s available for your next construction project:
- Ground Face Finish. Our Ground Face CMU is ground on at least one side, giving it a smooth, rich finish. With 20 standard colors, you’ll have plenty of options for combining colors, but we can also customize the pigment for your designing requirements.
- Split Face Finish. This textured block comes in the standard Split Face finish, Split Wide Profile and Split Fluted to satisfy a wide range of architectural looks. The depth and dimension of this design is a favorite for a variety of interior and exterior building projects and, like many of our CMU’s, can be used at or below grade.
- Antique Finish. Our Antique CMU is finished with a shot blast that beautifully exposes the stone beneath. We have several standard colors, and if they don’t suit your needs, we can customize the color just for your project. This block provides a fine, weathered look with a rustic texture that is used for both interior and exterior building.
- Monarch Traditional. You get the look of clay brick with the quality of a block in our Monarch Traditional line. These CMU’s are the length and depth of a regular block but the height of a standard brick. You can use this block at and below grade. We have designed them to meet ASTM-C90 standards for load-bearing concrete masonry.
- Elite CMU. No need to lay block and then face it with ceramic tile for interior applications. Our Elite CMU is an outstanding building material for both interior and exterior excellence. With color choices like salmon and gun metal, these filled and polished blocks are ideal for large commercial projects such as schools or municipal buildings needing that touch of color and style. Faces are ground and then filled with an acrylic resin filler. After polishing, they are sealed with our Volatile Organic Compounds (VOC) compliant sealer.
- Recycled CMU. Our “Eco-Smart” Recycled CMU is produced in our ground face and split face design. With a minimum of 30% recycled material, this is the popular choice for your environmentally-focused project. The recycled content will contribute LEED (Leadership in Energy and Environmental Design) points for your sustainable endeavor.
- Legacy Stone. Our Legacy Stone is an architectural veneer block that shows off the aggregate content of the block. It’s manufactured with a strength of 8500 psi and less than 5% absorption. We have four different finishes in our Legacy line which are often intermixed in a single project for visual appeal and structure:
- Linear Collection – two finishes on one block: ground face and shot blast. The width of each band is customizable to fit unique designs, and there are deep scored lines between the two different finishes.
- Textured – finished with a shot-blasted face, giving slight texture and dimension.
- Terrazzo – finished with a ground face, smooth and polished defines this concrete block unit. It’s often used for banding stripes.
- Chiseled Face – finished to resemble the look of cut limestone, these stones are often used for accent bands to break up large sections of one color and texture.
Select your desired block in a variety of specialized shapes for specific construction applications. We manufacture special forms of concrete block for construction of bond beams, control joints, radiused corners and many other architectural plans.
All Nitterhouse architectural CMU’s are sealed with a VOC-compliant, water-based acrylic resin sealer and should be coated with another sealing treatment when masonry work is complete. We also add a water repellent admixture to all our concrete block batches to reduce absorption and permeability. We provide this admixture to be added to the mortar when laying the masonry walls.
Masonry Block for Sound Building and Creative Design
Being in business for over 90 years, we’ve been expanding our product line and production capabilities as technology and best practices have changed. From the business ambition of mason William L. Nitterhouse making his own block in his garage to the fifth generation family line that handles our stone production today, we’ve made it our business to provide the best in quality, options and design.
In the future, the block manufacturing industry will continue to introduce new shapes, sizes and economic advantages to building construction. Energy efficiency and durable structures will continue to be at the forefront of new developments. Our designers have created superior products that have proven to be a harmonious blend of aesthetic appeal and structural dependability for any type of building.
Whether you have a community center to build or a high-rise to develop, you’ll find we can deliver just what you need to make your project exceptional. Check out our full line of Architectural Concrete Block and discover the diversity that will give you designing flexibility.