FREQUENTLY ASKED QUESTIONS
Is there a recommended viewing distance for acceptance of concrete masonry units (CMUs)?
Yes. ASTM C90 specifies a viewing distance of not less than 20-ft. However, this viewing distance is often misused. The most common ways that the ASTM C90 viewing distance has been misused are:
Viewing the completed wall assembly and not only the CMUs
Viewing CMUs at less than 20-ft
Viewing CMUs under direct lighting, and not diffused lighting. According to ASTM C90, the CMUs are viewed specifically for non-permitted chips, cracks, and other imperfections.
ASTM C90 Section 7.2 states; “Where units are to be used in exposed wall construction, the face or faces that are to be exposed shall not show chips or cracks, not otherwise permitted in 7.1.2 and 7.1.3, or other imperfections when viewed from a distance of not less than 20-ft under diffused lighting.”
NCMA FAQ 11-14 includes the following commentary:
Section 7.2 Commentary Discussions
ASTM C90 is a manufacturing standard – addressing the minimum requirements for block. It does not cover design, application, workmanship, etc. – each of which is necessary for the successful application of a C90-compliant concrete masonry unit. It is often interpreted that the 20-foot criterion above applies to the units that are installed. While this requirement could be applied as such, its true intent is for assessing units prior to their installation – again, because this is a product standard. When applying these limits to units that have already been installed, one should note that units may become damaged between the time they were delivered and the time they were installed. This should be taken into consideration. One reason that these requirements are applied to a finished assembly is because there are not standardized means of assessing workmanship or appearance of completed masonry assemblies.
Is there a recommended viewing distance for acceptance of concrete masonry units (CMUs)?
Yes. ASTM C90 specifies a viewing distance of not less than 20-ft. However, this viewing distance is often misused. The most common ways that the ASTM C90 viewing distance has been misused are:
Viewing the completed wall assembly and not only the CMUs
Viewing CMUs at less than 20-ft
Viewing CMUs under direct lighting, and not diffused lighting. According to ASTM C90, the CMUs are viewed specifically for non-permitted chips, cracks, and other imperfections.
ASTM C90 Section 7.2 states; “Where units are to be used in exposed wall construction, the face or faces that are to be exposed shall not show chips or cracks, not otherwise permitted in 7.1.2 and 7.1.3, or other imperfections when viewed from a distance of not less than 20-ft under diffused lighting.”
NCMA FAQ 11-14 includes the following commentary:
Section 7.2 Commentary Discussions
ASTM C90 is a manufacturing standard – addressing the minimum requirements for block. It does not cover design, application, workmanship, etc. – each of which is necessary for the successful application of a C90-compliant concrete masonry unit. It is often interpreted that the 20-foot criterion above applies to the units that are installed. While this requirement could be applied as such, its true intent is for assessing units prior to their installation – again, because this is a product standard. When applying these limits to units that have already been installed, one should note that units may become damaged between the time they were delivered and the time they were installed. This should be taken into consideration. One reason that these requirements are applied to a finished assembly is because there are not standardized means of assessing workmanship or appearance of completed masonry assemblies.
Is there a recommended viewing distance for acceptance of concrete masonry units (CMUs)?
Yes. ASTM C90 specifies a viewing distance of not less than 20-ft. However, this viewing distance is often misused. The most common ways that the ASTM C90 viewing distance has been misused are:
Viewing the completed wall assembly and not only the CMUs
Viewing CMUs at less than 20-ft
Viewing CMUs under direct lighting, and not diffused lighting. According to ASTM C90, the CMUs are viewed specifically for non-permitted chips, cracks, and other imperfections.
ASTM C90 Section 7.2 states; “Where units are to be used in exposed wall construction, the face or faces that are to be exposed shall not show chips or cracks, not otherwise permitted in 7.1.2 and 7.1.3, or other imperfections when viewed from a distance of not less than 20-ft under diffused lighting.”
NCMA FAQ 11-14 includes the following commentary:
Section 7.2 Commentary Discussions
ASTM C90 is a manufacturing standard – addressing the minimum requirements for block. It does not cover design, application, workmanship, etc. – each of which is necessary for the successful application of a C90-compliant concrete masonry unit. It is often interpreted that the 20-foot criterion above applies to the units that are installed. While this requirement could be applied as such, its true intent is for assessing units prior to their installation – again, because this is a product standard. When applying these limits to units that have already been installed, one should note that units may become damaged between the time they were delivered and the time they were installed. This should be taken into consideration. One reason that these requirements are applied to a finished assembly is because there are not standardized means of assessing workmanship or appearance of completed masonry assemblies.