What manufacturing standards apply to block?

ASTM C90 Standard Specification for Loadbearing Concrete Masonry Units outlines the material specifications for block. ASTM C140 Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units provides testing methods.

Are block all one weight?

No. Block are manufactured to meet ASTM C-90 which allows for three weight categories: Normal – 125 pcf or greater Medium – 105 to 125 pcf Light – 85-105 pcf

We are designing a two story office building, is Medium Weight my only block choice?

While typical, Medium Weight units are not the only choice for buildings. Fact is that block weight is very much dependent on your structural engineering needs, which will be impacted by building design and loading requirements.

My project specification is calling for Medium Weight block, but structural drawings call for Light Weight Block. Can I just use Medium Weight?

An RFI should be submitted to resolve the conflict between the architectural call out and the engineering call out.

Does Block Color impact test results?

Color oxides will not have an impact on test results.

Does Block Configuration impact test results?

Yes, configurations can have an impact on test results which is very much dependent on the test being performed. ASTM C-140 Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units provides methods to normalize these impacts. For instance, while many labs have equipment large enough to test 8x8x16 units they typically do not have the capacity to test 12x8x16 units. C-140 allows for representative coupons to be cut and tested instead.

Both Unit Strength and Prisms requirements are called for in my project. Do I need to satisfy both?

Engineers will call out the requirement necessary for each specific project. By Code, only one method is necessary for compliance. In these situations it is best to submit an RFI to clarify method.

Do block weight mix designs have an aesthetic impact on block with exposed aggregate finishes?

Yes. Each mix design is formulated to achieve a specific density range. In order to do so the mix of aggregates will vary weight to weight. These differences will have an impact, in all finishes and is highly noticeable on exposed aggregate finishes – Split Face, Shot Blast and Burnish. Please contact your local architectural representative to view samples.

Will the different weight categories impact precision color?

Light, medium, and normal weight units will differ in all finishes. In the Precision finish the difference is primarily due to cement content. Oxides used to color CMU bind to the cement. Since each mix design has a slightly different cement content, you will see variations in color between block densities.

Why do block vary slightly in color from block to block?

Block are manufactured using locally harvested aggregates (rock & sand) and other light weight aggregates. These aggregates are naturally occurring and will have slight variations which be noticeable in the finished block.

Do veneers have to be mechanically anchored or can they be installed with using just veneer bonding mortar?

CBC has specific language regarding CMU veneers. The base factor is weight, so all veneers that exceed 15lbs per square foot must be mechanically anchored. Veneers that fall under 15lbs per square foot can be adhered using bonding mortars as long as they meet dimensional restrictions. Projects subject to DSA oversight will have more stringent requirements. Please contact your local ORCO architectural rep for more info.

The CMU building I am designing needs an R-19 at the walls. Can I do that with CMU?

The R-19 requirements are typically for low mass walls. In a nutshell, low mass = greater R-value needs. Heavy Mass = lower R-value needs. CMU is considered a Heavy Mass Wall under CBC Title 24. In many cases 8” fully grouted block will meet basic prescriptive requirements. Your ORCO Architectural Representative can provide more information to assist you.

Are there ways to increase the R-value of block?

The use of pre-insulated masonry units can assist you in exceeding Title 24 requirements. At an R-14 Hi-R-H units far exceed the code requirements for heavy mass walls. This can get you well on your way to meeting a specific percentage above Title 24 requirements for CalGreen or for any green building rating system. In addition, standard CMU as part of a wall system can accomplish similar results. Your ORCO Architectural Rep can provide more information to assist you find a solution for your project.

Can I get a 4 hour fire rating from a CMU wall?

Per California Building Code Table 720.1 an 8” solid grouted CMU wall is rated at 4 hours.

The walls in the classroom I am designing need an STC Rating of 55. Will a CMU wall meet that requirement?

An 8” solid grouted medium weight CMU wall has a calculated STC Rating of 56. Using a denser block, a thicker block or adding furring strips and gypsum wallboard will increase that rating.

What is IWR and what does it do?

IWR (Integral Water Repellant) is an emulsion which is added to the cmu mix during production. This additive helps to reduce efflorescence and aids in resist moisture migration and wind driven rain. Please visit for more info.

What is Efflorescence?

It is a crystalline deposit that can form on the surface of masonry. Typically resulting from salts naturally found in aggregates or water. These salts can surface after a rain event or if the walls are subject to water exposure. Efflorescence can be cleaned using industry standard cleaning products. In many cases efflorescence will stop on its own after the first few rain cycles.

Are there added costs to building with 4” high masonry?

Yes. There will be increased material cost as you will need twice as many units to build the same area. Also, although the units are smaller and half the weight, the mason will have to touch twice as many units which reduces production time and increases labor costs.

What types of finishes are available for CMU?

CMU are manufactured in 4 typical finishes for standard CMU configurations: Precision, Split Face, Shot Blast and Burnish. We also offer Slump block which has an Adobe brick look.

Are veneers available in all finishes?

Veneers are available in a wide variety of finishes. Veneer size and configuration has an impact on availability. Contact your local Architectural rep for more info.

What is the weight per sq ft for veneers?

This can vary by veneer type and thickness. A standard medium weight 8x2x16 veneer is approximately 14 lbs per sq ft. Contact your local Architectural rep for more info.

How much does a standard block weigh?

Block weight will vary by size and configuration. A typical Medium Weight 8x8x16 weighs approximately 32 lbs per unit.

What is the best way to complete a corner using 12” wide units?

There are a few options to complete 12” corners. The National Concrete Masonry Association offers a TEK specifically on corner details TEK 05-09A – Corner Details