FAQ: Concrete Masonry Units

A concrete block’s “Configuration” refers to the block’s shape. A standard configuration is easy to identify: A rectangular block with two closed cells (holes) and a center dividing wall between the cells. Other configurations vary in terms of open or closed cells, number of cells, and cell sizes. 

ORCO’s Resources page includes documentation for CMU Configurations organized by block height.  

Concrete block cells matter for several reasons: hollow cells make concrete block easier to transport and lay than solid block. Additionally, the size and placement of cells is important to know for aligning block when building walls, and projects using rebar for reinforcement will need to know where and how large a concrete block’s cells are. 

A concrete block’s cell size will vary depending on several factors:  

First, the block’s cell size depends on the finish used. Smooth finishes such as Precision and Burnish tend to have larger cells than textured finishes such as Split Face and Shot Blast.  

Second, the cell size is also dependent on configuration. Open-end units, for example, are shaped differently within the cell area than a standard block. 

Check the configuration documents found on our Resources page for quick measurement references for all block configurations. 

Two primary factors affect the weight of our concrete blocks: the mix design (also known as the “block weight”) and the configuration (i.e. the “shape” of the block). 

ORCO produces blocks in three mix designs: in order from heaviest to lightest, they are Normal Weight, Medium Weight, and Light Weight. In general, lighter block comes at additional cost. 

Configurations such as open-ended units affect the weight of the block due to having less material than a standard concrete block. 

Your quantity of concrete block per pallet containing your order will vary depending on the configuration and block height. 

Various configurations may stack differently on a pallet than others, resulting in slight variation on the number of blocks per pallet.  

In general, the shorter the block height, the more blocks can be added to a single pallet. 

Refer to the table below for a general guide demonstrating these differences for several configurations. Be sure to refer to ORCO’s concrete block price list for specific counts of all configurations and block heights, available from your ORCO sales representative.

• All weights are approximations based on ORCO Riverside production, and are subject to variation. 
• Wet block takes on considerable weight, and moisture retention can affect actual weight. 
• All weights listed are estimated, to be used as a guideline only. 

Disclaimer: ORCO BLOCK & HARDSCAPE RESERVES THE RIGHT TO ASSUME NO RESPONSIBILITIES ON EITHER THE BLOCK WEIGHT OR PALLET WEIGHT, NOR DOES ORCO BLOCK & HARDSCAPE ASSUME ANY RESPONSIBILITY FOR TRUCK LOAD WEIGHTS. IN CRITICAL SITUATIONS, ALL LOAD WEIGHTS SHOULD BE RECHECKED BY THE TRUCKING COMPANY OR PURCHASING COMPANY. ORCO BLOCK & HARDSCAPE ASSUMES NO RESPONSIBILITY REGARDING OVERLOADED VEHICLES.

The number of CMU needed per square foot of wall depends on two factors: the height and length of the block, and the square footage of the wall project. 

As a general guideline, for 8’’ inch high units, divide the square footage of your project by .0889 and round up. For 4” inch high units, instead divide the wall area by 0.444 and round up.  

Many online resources exist to apply these calculations for your convenience. No matter what resource you use to estimate your total block needs, you may want to consider adding 5-10% additional total unit quantity as a precaution. Having some additional units above the exact estimate can cover units lost due to breakage, units used for cuts, and potential layout adjustments during a project. 

We do not offer a specific 12” pilaster cap. For 16” unit, we recommend using our 19x4x19’’ Bevel Cap to complement our block the best.  

Yes – please click this link to view our CMU Product Data Sheet, or visit our Resources page. 

ORCO sells only to licensed contractors and retailers. If you are a homeowner, we’re happy to help you find the best local ORCO dealer in your area – simply fill out our Dealer Request Contact Form, and we’ll respond promptly with recommended local retail locations to supply your project. 

For professionals, please complete our Sales Contact Form with as many project details as possible, and our sales team will follow up promptly to support your order. 

Use either (a) testing per ASTM E119 or (b) calculation per ACI/TMS 216.1. Ratings depend on equivalent thickness, aggregate type (lightweight vs. normal weight), grouting). Standard 6–12-inch CMU assemblies commonly achieve 2–4 hr.

Detail the wall as a rainscreen where possible, specify integral water repellent (IWR) in units and mortar, include flashing/weep paths, and select a compatible sealer after construction cleaning. For existing efflorescence: dry brush and rinse first; escalate with manufacturer-recommended cleaners only if needed. 

Mass helps. STC for CMU walls is determined per TMS 0302 methods; values increase with thickness, density, grouting, and finishes (e.g., plaster/gypsum). For façades, consider OITC in addition to STC. Use TEK tables during DD and verify in specs. 

Yes—CMU is a mass wall. You can comply prescriptively (R-/U-tables for mass walls) or via U-factor/trade-off/modeling paths. TEK 06-02C lists R/U values for single-wythe, and TEK 06-16A provides heat-capacity (thermal mass) data; energy codes allow lower added insulation for mass walls versus framed walls.

Empirical rule of thumb from NCMA TEK 10-2: maximum spacing is the lesser of 25 ft or 1.5 × wall height, with joints at changes in height/thickness, re-entrant corners, and near large openings. Engineered alternatives (TEK 10-3) allow spacing to vary when sufficient horizontal reinforcement is provided.