Iano's backfill

MasterFormat 2004 Released

The Construction Specifications Institute (CSI) has released the final version of its updated MasterFormat system for organizing construction specifications. Dubbed MasterFormat 2004, this significant revision provides new divisions dedicated to disciplines previously under-represented, expands the numbering system to allow for greater depth of content, and also attempts to minimize disruption of the system's core architectural divisions.

The number of Divisions, the largest organizational groupings in the system, increases from 16 to 49. Major changes include:

• Division 02 Existing Conditions
• Divisions 20 - 29 Plumbing, HVAC, Electrical, Fire Suppression and other "Facilities Services"
• Divisions 20 - 39 Sitework, Transportation, Utilities, and other "Site and Infrastructure"
• Division 40 - 49 industrial "Process Equipment"

The numbering system itself has been expanded from five digits to six to create more space for individual Section numbers. For example, Clay Unit Masonry, previously Section 04210, is now Section 042100. Section numbers themselves are organized into two-digit groups, each group representing a finer level of subdivision. So in the previous example, '04' is referred to as the Division or "level one" designation, the middle '21’ is the level two designation, and the final '00' is level three. Level four designations can also be provided as two-digit suffixes. An example of how these level designations are used to subdivide specification content looks like this:

• Section 042000 Unit Masonry
• Section 042100 Clay Unit Masonry
• Section 042113 Brick Masonry
• Section 042113.13 Brick Veneer Masonry

Thankfully for architectural specifiers, Divisions 03 Concrete through 14 Conveying Equipment have undergone only modest updates, aside from the expanded numbering system itself.

More Information
_More information on the MasterFormat 2004 system is available on CSI's All About MasterFormat 2004 Edition page. A copy of the complete new system can also be downloaded from this page.
_The MasterFormat system and its role in the construction industry is discussed on pages 11 - 12 of the textbook. Section numbers relevant to specific content are also provided close to the end of each chapter.

Recent News In Structural Steel Design

Steel Connection Design
30 Good Rules for Connection Design, Modern Steel Construction, May 2004, discusses principles of economical steel connection design. Some examples:

• Limit the number of bolt diameters used (to reduce errors in fabrication or the field).
• Avoid different grade bolts with the same diameter.
• Avoid overhead welding.
• Limit maximum fillet weld size to 5/16-inch (the maximum size that can be completed in a single pass). Longer, smaller thickness welds are preferred over shorter, thicker welds.

For structural designers and others interested in gaining a better appreciation of steel connection design friendly to fabricators and erectors, this article is a good reference.

Architectural Exposed Structural Steel
Architecturally Exposed Structural Steel, Modern Steel Construction, May 2003, discusses guidelines for the design and specification of exposed steel structure. This lengthy article includes extensive sample specification language, commentary, color photographs, and detailed cost data. This article is recommended reading for architects and specifiers concerned with this type of construction.

The information contained in this article is also available on the American Institute of Steel Construction web site's AESS Guide Specification page. This information has also appeared as a continuing eductation series article in the 06.04 issue of Architecture Record magazine.

Propriety Steel Connection for Seismic Load Conditions
SOM receives patent for novel seismic structural joint, Building Design & Construction, describes a new structural steel joint system designed and patented by architecture/engineering firm Skidmore, Owings & Merrill. The "Pin-Fuse" joint is a hinged connection that remains rigid under moderate structural loads. However under extreme seismic load conditions, the joint may rotate while dissapating the dynamic energy of the seismic forces. According to the article, the Pin-Fuse joint can be used with either steel or concrete structural frames, and should allow reduced structural frame member sizes in comparison to alternative design strategies for such extreme loadings. (At the time of this writing, this article could be viewed online here.)

More Info
For more on the fundamentals of steel connection details, see pages 386 - 395 in the textbook.

Deciphering ASTM Standards for Structural Steel W-Shapes

[View within mini-mill melt shop where recycled steel is prepared for processing into new steel]

A recent article on this site, Structural Steel Materials Standards, described recommended ASTM standards for specifying various structural steel shapes and components. For those not regularly involved in the reading and writing of specifications, deciphering the meaning and significance of ASTM standards can be a challenge. As a way of introduction, the following provides some explanation regarding ASTM standards commonly applied to structural W-shapes.

Material Properties
One of the important functions of specifying steel standards is to define the material properties of the steel used on a project. The following table summarizes some commonly used designations for structural steel and several properties of the steel specified. As can be seen from the table, by specifying an ASTM designation (and in some cases also a Grade), minimum structural properties of the steel are established:

ASTM Designation	Minimum Yield Stress (ksi)	Minimum Tensile Stress (ksi)
A36	36	58-80
A572 Grade 50	50	65
A572 Grade 60	60	75
A572 Grade 65	65	80
A992	50-65	65

Other materials properties not shown in the above table may also influence the choice of steel type. For example, even though A992 steel and A572 Grade 50 steel appear comparable in the chart above, the relatively newer A992 designation is preferred for other aspects of its material definition.

Method of Manufacture and Cost
Differences in ASTM structural steel standards also reflect changes in steel manufacturing processes. For many decades, structural steel was manufactured mostly from raw materials and was formulated to meet the requirements of ASTM A36. Higher-strength steel was only specified where the need for its superior structural properties justified the significant additional cost associated with such material.

Today, most structural steel is manufactured in so-called mini-mills. By relying on scrap steel as the primary raw ingredient for manufacturing new steel, these newer mills are able to produce higher strength alloys such as ASTM A572 or A992 at lower cost than traditionally manufactured A36 steel. Consequently high-strength steel is now routinely specified for structural W-shapes.

How Are Standards Created and Enforced?
ASTM standards are developed through a consensus process involving industry stakeholders such as producers, consumers, users, government bodies, and researchers. ASTM itself is a not-for-profit organization. It has no enforcement mandate, and the standards it publishes are strictly voluntary.

ASTM standards may become defacto standards when they are adopted by the trade association that represents a particular industry. For example, in the case of the structural steel standards dicussed in this article, definitive recommendations for their use are found in the American Institute of Steel Construction's (AISC) LRFD Manual of Steel Construction (3rd Edition).

ASTM standards may change from voluntary to required when they are adopted by reference in building codes or other regulations. For example, the 2003 International Building Code makes AISC's design standards mandatory in paragraph 2205.1 General, which reads in part:

The design, fabrication and erection of structural steel for buildings and structures shall be in accordance with either the AISC-LRFD, AISC 335, or AISC-HSS...

In this way, ASTM standards that are part of the referenced AISC standards become mandated through the building code. (In other cases, the building code may directly reference ASTM standards themselves, rather than indirectly referencing them through other publications as in this example.)

Structural Steel Materials Standards

Are you Properly Specifying Materials?, Modern Steel Construction, January 2004, provides guidance on application of ASTM standards to specifying structural steel and related components. According to this article, preferred standards include:

Standard	Application
ASTM A992	Structural W-Shapes
ASTM A572, A913	Structural W-Shapes with higher yield and tensile strength than A 992
ASTM A588	W-Shapes of "weathering steel"
ASTM A36	Structural M-, S-, HP-Shapes, Channles, Angles, Plates, Bars, Threaded Rods
ASTM A53 Grade B	Steel Pipe
ASTM A500 Grade B	Round and Rectangular Tubes (Hollow Structural Sections)
ASTM A325, A490	High-Strength Bolts
ASTM A307	Common Bolts
ASTM A563	Nuts
ASTM A436	Washers
ASTM A1554	Anchor Rods

Information regarding steel grades and yield stresses is also provided.

For those who write or read structural steel specifications, this is a useful article. Companion articles in the same issue address availability of various shapes and grades, designing with high-strength grades, and related topics.

More Information:
Followup article Deciphering ASTM Standards for Structural Steel W-Shapes will provide some basic guidance on making sense out of ASTM structural steel standards.
Steel alloys, shapes, and fasteners are discussed on pages 374 - 382 of the textbook.
ASTM Standards and their summary scopes can be viewed online at ASTM Standards Search.

More On Concrete Floor Flatness

SpecPress, the newsletter for subscribers to the ARCOM MasterSpec system, has more to say about the contradictions faced in the specification of flatness of concrete slabs as previously discussed on this site in articles Concrete Floor Flatness and Concrete Slab/Floor Covering Issues. In The Concrete Floor Tolerance/Floor Covering Conundrum (Volume 9, Issue No. 4, Fourth Quarter 2003), Bruce Suprenant identifies the following basic problems:

• Concrete placement in Division 3 relies on the F-number system to specify floor flatness. Finish floor coverings specified in Division 9 rely on the straightedge method. There is no direct correlation between the two methods.
• The criteria for measuring F-numbers specified in Division 3 do not satisfy the requirements for Division 9 finishes. For example, F-number measurements may not be taken across construction joints, they may not be taken within 2 feet of a slab penetration, and they must be taken within 72 hours of the initial slab pour. However, floor coverings typically are applied across construction joints, close to slab penetrations, and after the slab is fully cured.
• Different floor coverings applied to different sections of the same slab may require different slab finishes (such as hard trowel, broom, etc.), even though it is often not practical to specify different finishes across a single pour.

Suprenant recommends the following possible approaches to dealing with the contradictions:

The specifier can require an arbitrarily higher initial floor flatness hoping that the final, cured slab will meet minimum requirements. The difficulty with this approach is that there is no method to predict final flatness based on flatness measured within the intial 72-hour measurement window.

Additional reinforcing can be added to the slab in order to reduce curling that occurs during curing. Suprenant claims that with additional reinforcing, control joints are not effective, and thereby money can be saved by "not cutting and filling joints".

Assign responsibility to grind or patch the floor as required to the floor covering contractor(s). The advantage to this method is that responsibility for achieving the required floor flatness is put into the hands of the floor covering contractor whose product dictates the flatness requirement. Suprenant suggests specifying an allowance amount in the specification to be applied toward anticipated grinding and patching.

Preservative Treated Lumber II

Pressure-Treated Wood: The Next Generation, Fine Homebuilding January 2004, has more to say about the new wood preservatives coming to market and their higher corrosiveness as discussed here previously. In summary:

• It's the high concentration of copper in alkaline copper quat and copper azole that give these preservatives their potency, and that makes them as much as 5 times more corrosive than traditional CCA-treated lumber.
• FH recommends stainless steel hardware and fasteners wherever possible. Where hot dip galvanized material is used, a G-185 rated coating is recommended. G-185 hot dip galvanized steel has 1.85 ounces of zinc per square foot of metal, compared with 0.90 or 0.65 ounces per square foot for the more commonly available G-90 or G-65 coatings. Electrogalvanized fasteners, such as expansion bolts, should be rated Class 40 or higher (the electrogalvanizing Class scale ranges from a low value of 5 to high value of 110). Polymer coated screws may also acceptable. (Author's note: Simpson Strong-Tie recommends minimum Class 55 for electrogalvanized fasteners.)
• Avoid any contact between these treated lumber products and aluminum sheet metal or fasteners, as they will corrode quickly. Copper sheet metal is OK.
• Special care must be taken at locations such as mud sills, which must be preservative treated lumber, but are not normally associated with corrosion resistant fasteners. Nails at the bottom edge of the wall sheating that are driven into the mudsill, foundation anchor bolts and straps, and toenails fixing rim joists and floor joists to the mud sill are all possibly at risk of accelerated corrosion.
• Lumber is rated by end-use application. In order of increasing preservative concentration, categories are Decking, Above Ground, Ground Contact, and Permanent Wood Foundation.
• New borate based preservative forumulations, which do not rely on copper for their potency, are also coming to market. According to Fine Homebuilding, borates are not corrosive and have a low toxicity.

Designing with Metals: Dissimilar Metals and The Galvanic Series

The galvanic series is a list of metals arranged in order of their relative electrical potential. A simple version of the galvanic series is shown in Figure 16.55, page 604 of the textbook. When two metals are in contact in the presence of moisture, their locations within the series indicate the risk of corrosion due to the flow of electric current between them. The closer the two metals on the list, the less the difference in electrical potential, and the less the risk of corrosion. The further apart the two materials on the list, the greater the risk of corrosion. The following are some guidelines for working with dissimilar metals and interpreting the galvanic series.

Avoid contact between metals far apart on the galvanic series.
Virtually every student of building technology is taught this most basic fact about the galvanic series. However, when presented in its usual list form, the galvanic series provides only minimal guidance on judging the relative differences between metals and evaluating their potential incompatibility. A more complete picture of the compatibility of metals can be constructed when numeric values for the metals' electrical potential are attached to the list as well.

This chart lists common architectural metals along with their ranges of relative electrical potential. As with the galvanic series, metals are arranged in order of increasing potential, but in this case, the relative differences between various metal types are more readily apparent.

For example, in the chart above consider the aluminum bronze alloy group and the next metals listed directly above and below. We can see that between the aluminum bronze alloys and the brass alloys directly below (naval, red, and yellow brasses), the relative difference between these metals is small. On the other hand, the difference between aluminum bronzes and mild steel, cast iron, and wrought iron directly above is many times greater. In fact, one must read down the list nine or more metals below aluminum bronze before the electrical potential difference is comparable to moving up only to the first metals above.

With quantified potential differences between metals, the galvanic series can also be used to estimate the compatibility of different metals under varying environmental conditions using the following rules of thumb:

• In coastal, very high humidity, or other harsh environments, galvanic metal pairs should be limited to those with a potential difference no greater than 0.15 volts.
• In moderate environments, metal pairs should have a potential difference no greater than 0.25 volts.
• In environments with controlled humidity and temperature, potential differences as great as 0.50 volts may be acceptable.

For example, consider again the aluminum bronze alloy group. In a harsh environment, the designer may opt to limit metals to be used in contact with this alloy group to other bronze alloys, brasses of various types, copper, tin, and 400 series stainless steel. On the other hand, in a controlled environment, aluminum bronze might safely be combined with any other metal listed on the chart, with the exception of zinc and galvanized steel.

Based on these rules of thumb, metals listed in the chart have been color-coded into groups that fall within potential difference ranges of roughly 0.20 volts. Metals within each of these groups may be considered least corrosion prone when used together in normal architectural conditions.

Avoid smaller anodes in contact with larger cathodes.
On the chart above, the more negative end of the potential scale is noted as anodic or active, and the more positive end of the scale as cathodic or passive. When different metals react galvanically, an exchange of electrons takes place between the two metals, with electrons flowing from the metal with greater negative potential (the anode) to the metal with lesser negative potential (the cathode). For example, if aluminum bronze and a 300 series stainless steel are used together, the aluminum bronze has a greater negative potential and will act as the anode, donating electrons to the less negative stainless steel, the cathode. On the other hand, if aluminum bronze is used with mild steel, mild steel has a greater negative potential and will act as the anode, donating electrons to the aluminum bronze, which in this case acts as the cathode. (A note on terminology: Literature on galvanic reactions often refers to cathodic metals as noble. These two terms are synonymous.)

To a chemist, the anode’s release of electrons is termed oxidation. In laymen’s terms this is known as corrosion. In other words, with any galvanic pair of metals, the anode corrodes as the galvanic reaction takes place. Controlling the rate of corrosion of the anodic metal is an important consideration in working with galvanic metal pairs. After consideration of the electrical potential difference between the two metals, the next most important factor governing the rate of corrosion of the anode is the relative surface area of the anode in comparision to the cathode. The smaller the surface area of the anode in relation to the cathode, the more concentrated the flow of electrons, and the faster the rate of corrosion. The larger the anode's surface area in relation the cathode, the more spread out the flow of electrons, and the less the corrosion. This principal, called the area ratio, often has important architectural implications.

For example, consider a sheet metal copper roof fastened with Type 304 stainless steel screws. The potential difference between the two metals is in the range 0.2 to 0.3 volts, so some corrosion effects may be expected under exterior conditions. In this galvanic pair, copper has a higher negative potential and will act as the anode and stainless steel will act as the cathode. However, since the surface area of the anode (the copper roof metal) is large in comparison to the surface area of the cathode (the stainless steel fasteners ), the corrosive effect on the copper is distributed over a relatively large area and greatly mitigated. In this case little if any long-term negative effect is anticipated. In fact, in practice, stainless steel screws are an accepted method of attachment for copper roofing.

As a counter example, consider a stainless steel sheet metal roof fastened with copper nails. In this case, the surface area of the anode (the copper fasteners) is very small in relation to the surface area of the cathode (the stainless steel roof metal), the flow of electrons from the anodes is highly concentrated, and rapid corrosion of the fasteners is expected.

In fact, the rate of corrosion of the anode in a galvanic metal pair is directly related to the numeric area ratio of the two metals. That is, if the surface area ratio of cathode to anode is doubled, the rate of corrosion of the anode is also doubled. Likewise, if the area ratio is halved, the rate of corrosion of the anode is halved.

Avoid Fasteners Acting as Anodes
The previous examples illustrate an important guideline, that fasteners should generally be selected to avoid taking on the role of anode in a galvanic reaction. Due to their normally small surface area in relation to the materials being fastened, such fasteners will be at risk of rapid corrosion. Thus when fastener and base metal differ, the fastener metal should be selected to be cathodic in relation to the base metal. When two dissimilar metals are joined with a third fastener, the fastener should be cathodic in relation to at least one of the other metals, so that it does not take on the role of anode in a galvanic reaction between the three.

There are many finer points regarding the selection of metal fasteners in relation to metals being joined, the building environment, and the particular application. This topic will be addressed more fully in a later article in this Designing with Metals series.

Avoid Rainwater Runoff From Cathode To Anode
Consider a sheet metal copper roof with a galvanized steel gutter. Rainwater flowing over the roof metal will pick up copper in solution and carry this dissolved metal into the gutter. When the dissolved copper and galvanized steel come into contact, these metals will react as a galvanic pair. Since the galvanized steel is anodic to copper, the gutter will be corroded. Alternatively, consider a galvanized steel roof and a copper gutter. In this case, dissolved zinc (from the galvanized coating on the steel) is carried into the copper gutter, where the zinc will act as the anode in the galvanic pair. In this case the copper gutter acts as the cathode and is not threatened with corrosion.

As a general rule with metal roof and wall systems, care should be taken that rainwater does not flow from metal surfaces that are relatively cathodic to others that are relatively anodic.

Treat Plated Metals According To Their Plating
When using galvanic series charts with plated metals, read from the position of the plating, not the base metal. For example, a cadmium plated mild steel fastener reacts according to the electrical potential of cadmium, not mild steel. Galvanized steel (a zinc metal coating on steel) reacts according to the electrical potential of zinc. Lead coated copper sheet will react according to the electrical potential of lead, not copper. Etc.

Understand Your Project Particulars
In practice, there are additional considerations that can influence the severity of the galvanic reaction between metals. For example, coastal environments tend to produce salt-laden precipitation that can significantly accelerate the reaction between galvanic metal pairs in comparison to non-coastal areas. Urban and industrial environments, with their relatively high concentrations of air pollutants, produce precipitation that is more acidic and conducive to corrosion than precipitation further from such areas. Perhaps less obvious is the potential for accelerated corrosion in some agricultural environments, where certain fertilizers are a known source of corrosive air pollutants.

The electrical potential of metals may vary depending on the medium in which the galvanic reaction takes place. In fact, most galvanic series, including the chart in this article, are based on the electrical potential of metals when immersed in flowing sea water. The designer should keep in mind that metals buried in soil, exposed to highly corrosive industrial solutions, or otherwise exposed to atypical environments may react quite differently from what is predicted by the standard galvanic series.

As one example, consider a 300 series stainless steel angle buried in mud. Due to a lack of free oxygen in such a soil condition, the stainless steel may not be able to maintain the passive layer that normally protects the underlying metal from corrosion. In this condition, the stainless steel surface can become more electrochemically active and assume a location in the galvanic series close to mild steel, a change in its electrical potential of approximately -0.5 volts. (For a discussion of stainless steel alloys and its active and passive conditions, see the related article Stainless Steel and Corrosion Resistance.) As another example, curiously, zinc may become cathodic to iron when immersed in hot tap water.

The particulars of a metal detail or assembly can also influence the rate of corrosion. For example, low-slope metal roofs, in which standing water can accumulate, may exhibit higher rates of corrosion in comparison to steeper roofs that shed water more rapidly and therefore remain dryer. Details that capture and trap water can also lead to accelerated corrosion in localized areas.

Approach Insulating Strategies Cautiously
One strategy for mitigating corrosion between metals is to insulate the metals from each other so that the electrochemical reaction can not take place. While this strategy is theoretically sound, in practice it must be approached with caution.

For example, consider a copper roof fastened with galvanized steel anchor clips. This is not a recommended assembly since the galvanized steel is anodic to the copper. Given the relatively small surface area of anchor clips in relation to roof metal, the anchor clips are expected to corrode rapidly. One way to attempt to overcome this problem might be to apply a non-conductive coating, such as asphalt mastic, to the anchor clips, thereby preventing electrical contact between the two metals. However, in practice, it must be assumed that some gaps will appear in the coating, either due to imperfect application or due to wear and tear over time as the metals expand and contract. In either case, where gaps occur, the galvanic reaction will proceed. Furthermore, given the even smaller area ratio between just these exposed areas on the anodes and the larger area of cathodic roof metal, the reaction will proceed in these areas at an even more accelerated rate than it would have otherwise.

In other words, applying insulating coatings to only the anode in a galvanic pair is strongly discouraged, as it may actually increase the risk of corrosion. When insulating coatings are used to prevent electrical conduction between galvanic pairs, the cathode should always be coated, whether the anode is coated or not.

As another example, consider a black rubber washer between a fastener and roof of different metals. If the washer contains a high percentage of carbon black (used to color the washer), it may be sufficiently electrically conductive to allow the galvanic reaction to proceed between the two metals. Furthermore, even with an insulating washer, the two metals remain in contact where the fastener penetrates the roof sheet, and the galvanic reaction can still proceed through this juncture.

Conclusion
The galvanic series is a powerful tool for evaluating the potential risk of corrosion between metals. However, to be used effectively, it must be applied knowledgeably and with consideration of factors that may influence the risk of corrosion between dissimilar metals. Wherever possible, past experience and local knowledge should be included in these considerations.

This is the second article in an occasional series on architectural metals.
Stainless Steel and Corrosion Resistance
Dissimilar Metals And The Galvanic Series (this article)
Next: Selecting Metallic Fasteners

For more information:
ASTM International's ASTM G 82 Standard Guide for Development and Use of a Galvanic Series for Predicting Galvanic Corrosion Performance includes the galvanic series, guidelines for its interpretation, and information on the deriviation of electrical potential values.
Corrosion Doctors and CorrosionSource.com web sites provide extensive information on many aspects of the corrosion of metals. See for example The Galvanic Series, Introduction To Design and Corrosion, Prevention of Galvanic Corrosion By Design, and Galvanic Compatibility
Department of Defense, Military Specification Finishes for Ground Based Electronic Equipment, MIL-F-14072D(ER) provides some useful guidelines and technical details for working with the galvanic series.

MasterFormat and Using This Site

This site is organized primarily according to the Chapter organization of the textbook. For site visitors wishing to locate content according to the CSI MasterFormat system, the following should be helpful:

MasterFormat 2004 Division	Textbook Chapters
Division 3--Concrete	Chapter 13: Concrete Construction Chapter 14: Sitecast Concrete Framing Systems Chapter 15: Precast Concrete Framing Systems Chapter 20: Cladding with Masonry and Concrete
Division 4--Masonry	Chapter 8: Brick Masonry Chapter 9: Stone and Concrete Masonry Chapter 10: Masonry Loadbearing Wall Construction Chapter 20: Cladding with Masonry and Concrete
Division 5--Metals	Chapter 11: Steel Frame Construction Chapter 12: Light Gauge Steel Frame Construction
Division 6--Wood, Plastics, and Composites	Chapter 3: Wood Chapter 4: Heavy Timber Frame Construction Chapter 5: Wood Light Frame Construction Chapter 6: Exterior Finishes for Wood Light Frame Construction (Siding, Trim, Exterior Construction) Chapter 7: Interior Finishes for Wood Light Frame Construction (Millwork and Finish Carpentry)
Division 7--Thermal and Moisture Protection	Chapter 2: Foundations (Waterproofing and Drainage, Basement Insulation) Chapter 6: Exterior Finishes for Wood Light Frame Construction (Roofing) Chapter 7: Interior Finishes for Wood Light Frame Construction (Thermal Insulation and Vapor Retarder) Chapter 16: Roofing Chapter 19: Designing Cladding Systems Chapter 21: Cladding with Metal and Glass
Division 8--Openings	Chapter 6: Exterior Finishes for Wood Light Frame Construction (Windows and Doors) Chapter 17: Glass and Glazing Chapter 18: Windows and Doors Chapter 19: Designing Cladding Systems Chapter 21: Cladding with Metal and Glass
Division 9--Finishes	Chapter 1: Making Buildings (Choosing Building Systems: Building Codes) Chapter 6: Exterior Finishes for Wood Light Frame Construction (Paints and Coatings, Exterior Painting) Chapter 7: Interior Finishes for Wood Light Frame Construction (Wall and Ceiling Finish, Flooring and Ceramic Tile Work) Chapter 22: Selecting Interior Finishes Chapter 23: Interior Walls and Partitions Chapter 24: Finish Ceilings and Floors
Facility Services Subgroup, Divisions 21 -- 28 (mechanical and electrical systems)	These systems are covered incidentally in: Chapter 7: Interior Finishes for Wood Light Frame Construction (Roughing in of Mechanical and Electrical Systems) Chapter 22: Selecting Interior Finishes (Installation of Mechanical and Electrical Services)
Division 31--Earthwork	Chapter 2: Foundations

Concrete Floor Flatness

Traditionally, requirements for concrete slab flatness were expressed as the maximum allowable gap under a 10-foot straightedge. For example, variation in an architectural concrete slab might be limited to 1/8 inch in 10 feet. Slabs to receive resilient flooring materials might be limited to 3/16 inch in 10 feet, and utilitarian slabs might be limited to 1/4 inch in 10 feet. While this standard may still be used on small projects, flatness requirements for most concrete slab work today are specified using the newer ASTM E1155 Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers.

ASTM E115, commonly called the F-number system, uses more precisely defined methods to establish requirements for both "flatness" and "levelness" of concrete floors. Flatness refers to the slabs waviness. Levelness refers to the slabs deviation from horizontality.

While the F-number system is more precise and more consistent in its results, it is also less intuitive. For example, requirements for a concrete slab to receive resilient flooring might be expressed as follows (higher number indicate closer tolerances, that is, a flatter, more level floor):

Flatness: Specified Overall Value (SOV): 35; Minimum Local Value (MLV): 24
Levelness: SOV:  35, MLV: 24

The specified overall value (SOV) is a value representing the floors overall flatness or levelness. The minimum local value (MLV) reflects deviations in flatness or levelness within any limited area. Though there is no direct correlation between straightedge measurements and F-number system values, the MLV for flatness is the closest measure comparable to the traditional straightedge measurement. According to ACI 117, F-number flatness (Ff) values correlate approximately as follows to the traditional straightedge measures:

Ff12:	1/2 inch in 10 feet
Ff20:	5/16 inch in 10 feet
Ff25:	1/4 inch in 10 feet
Ff32:	3/16 inch in 10 feet
Ff50:	1/8 in 10 feet

However, the above comparisons should be approached with caution. According to ACI, slabs specified with the traditional straightedge method generally do not meet the specified requirements. Therefore applying, for example, an F-number flatness of 50 where previously 1/8 in 10 feet was required may result in an unrealistically strict requirement.

From the perspective of an architect/specifier, working with the F-number system presents a number of issues:

• For most of us, F-numbers are more difficult to interpret than the traditional straightedge standard.
• F-number results, while more accurate, are more difficult to obtain. Testing a slab according to the F-number system requires specialized equipment and trained operators.
• According to ASTM E1155, F-numbers are measured within 72 hours of concrete placement. Therefore, they do not necessarily represent the final condition of the slab after more complete curing.

As one example of how these issues can affect a project, the American Society of Concrete Contractors, ASCC Position Statement #6, makes the point that F-number requirements established in the concrete sections of the project specification do not ensure that such slabs will necessarily meet the requirements of floor finish materials specified in other sections and installed later in the construction phase. This is true because floor finish manufacturers do not publish flatness requirements using the F-number system, and as noted earlier, F-numbers are measured early in the concrete curing process and do not necessarily reflect the final state of the slab after more complete curing.

In short, proceed with caution when attempting to set establish appropriate tolerances for concrete slab construction.

Further Reading:
Concrete Slab/Floor Covering Issues, on this site, discusses an inter-industry report on concrete floor issues, including flatness requirements.
The textbook discusses concrete slab construction beginning on page 505. Slab flatness is discussed on page 508.
The American Concrete Institute publishes technical papers on the use of the F-number system.
ASTM E1155 can be purchased from ASTM International.
At the time of this writing, The Face Companies - The 40 Most Asked Questions about F-Numbers is a good FAQ on the F-number system.

Concrete Slab/Floor Covering Issues

Summary Report On The Inter-Industry Working Group On Concrete Floor Issues (PDF) summarizes the content of a meeting of representatives from the construction industry, flooring manufacturers, specification bodies, and technical societies, convened to address problems frequently encountered in the application of various finish floor covering materials over concrete slabs on grade. Identified issues include:

Delays while waiting for concrete surfaces to dry or reach an acceptable pH level

Substrate cracks reflecting through many "bonded" floor coverings

Floor flatness variations that affect floor covering installation

Moisture-related floor covering failures, after installation, such as blistering, debonding, adhesive oozing, and microbial growth

This author does not recommend this document for the casual reader. However for professionals struggling with the issue of such floor covering failures, this represents an excellent summary of the state of what is known about these problems. For the student of construction, this document might also serve as a good example of how even seemingly simple applications--such as vinyl flooring adhered to a concrete slab on grade for example--can at times present a myriad of potential pitfalls.

More information:
Concrete Floor Flatness, on this site, discusses standard methods for setting the flatness of concrete slabs.