The following MFMA position statements were created to assist in the education of maple athletic flooring. They are created for those who do not have a detailed knowledge of the construction and/or post installation use and maintenance of athletic floors. Information contained herein is based on best industry practices and knowledge, however the MFMA, its members and employees, do not warrant the information contained herein as proper under all conditions. The MFMA reserves the right to revise these position statements as necessary. Questions concerning information contained in these position statements should be directed to Foster Specialty Floors. Please call Fosters at (888) 66-FLOOR or EMAIL us here.

ADA PRESS RELEASE

Proper installation of raised sport floors, especially in retrofit projects, can have implications for the sport floor contractor where vertical rises exceed ½" in public entrances. MFMA recommends in these instances the sport floor contractor confirms in writing with the architect, design professional or owner these areas meet Federal ADA, state and local access codes before installation begins.

It is the responsibility of the architect, design professional or owner to ensure the project meet Federal ADA, state and local access codes.

 
 

BLEACHER BLOCKING

MFMA refers all inquiries concerning subfloor bleacher blocking requirements to the individual flooring system manufacturer and the specified bleacher manufacturer. Variances in bleacher system design, loading, total weight, and operation make uniform specifications for subfloor blocking impossible.

CHATTER MARKS

Chatter marks, in a very moderate form, are fairly common in new maple installations where drum or riding sanders are used in the flooring surface sanding process.

 

MFMA has no written policy or specification regarding the appearance or frequency of chatter marks in our flooring installations. Generally speaking, minor chatter marks are apparent in scattered locations on most flooring installations. They are considered excessive if close-up inspection yields noticeable uneven or gouged areas of the flooring.

 

There can be a number of causes of chatter marks. The most common occurrence in the maple itself results from the use of drum or riding sanders on a surface with a degree of built-in "give." These are very different from chatter marks between layers of finish, which are typically seen when lighting is reduced and angled reflections are observed.

 

Between-coat buffing is desirable to ensure proper adhesion of successive coats of finish, and in fact is required under certain finish manufacturer warranties. Flooring appearance in these cases is akin to a fresh wax job on a black automobile -- when viewed at a specific angle under specific lighting conditions, marks are visible.

 

Chatter marks of this type are not damaging to the surface, nor will the marks impair the playability or performance of the system. Typically, the marks will soon begin to disappear as the oil-modified finish on the floor ambers with age.

 

The pace of ambering varies from product to product, but most color changes will take place between six months to fifteen months following the initial application. However, water-based finishes do not amber over time and if you think chatter marks are present, check the severity and contact your flooring installer.​

 
 
 
 

CONCRETE PADS UNDER FIXED BLEACHER SYSTEM

The placement of permanent concrete pads under large fixed bleacher banks has become more common in an effort to reduce installation costs in an area of a gymnasium floor that gets little use. The transition between such concrete pads and the adjacent wood floor often consists of a metal transition plate.

 

The use of concrete pads to support the bleachers in the closed position, and the installation of a transition plate to the wood floor system is, in many cases, an unworkable design for a motor-driven bleacher system — particularly a large bleacher system.

 

It is our opinion that the best solution to minimize potential difficulties that may occur with the combination of a resilient floor system and large bleacher banks is to install sufficient bleacher blocking under the location where the bleachers will rest in the closed position, and to extend the maple surface completely under the bleacher banks. The installation of solid wood blocking under the bleacher may be necessary to reduce or eliminate the deflection associated with heavy bleacher movement over a resilient wood flooring system. If cost is a concern, consider using a lower grade of flooring in the areas under the bleacher banks.

 

MFMA refers all inquiries concerning subfloor bleacher blocking requirements to the individual flooring system manufacturer and the specified bleacher manufacturer. Variances in bleacher system design, loading, total weight, and operation make uniform specifications for subfloor blocking impossible.

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CONCRETE SLAB CONFIGURATION

DEERFIELD, IL - Concrete slab configuration is very important in the success of a new maple floor installation. Placing a below-slab vapor barrier directly beneath the concrete slab is proper and typical. Placing any type of fill material between the below-slab vapor barrier and the concrete slab may cause moisture-related problems with the finished maple surface.

 

MFMA requires the general contractor to provide a concrete slab troweled smooth and flat to a tolerance of 1/8” in a 10’ radius, subject to the approval of the FSF wood flooring contractor. By placing sand between the vapor barrier and the slab, a flatter concrete slab with less initial curling can be produced. However, this new configuration allows the sand to possibly act like a sponge -- trapping moisture within the sand layer during the concrete pour. Over time, trapped moisture can migrate up through the concrete slab and cause moisture-related difficulties with subfloor components and the finished wood flooring surface.

 

The only MFMA recognized method for reading concrete moisture levels within a slab is by testing its relative humidity. Please refer to the instructions of the manufacturer’s relative humidity test kit for complete details on how to administer the test correctly. MFMA recommends the relative humidity level for a concrete slab for anon-glue-down maple floor system be 85% or lower and for glue down systems the concrete slab relative humidity level should be 75% or lower before installation. For concrete relative humidity conditions above MFMA's recommendation consult your FSF Sport Floor Contractor.

CONCRETE SLAB FITNESS

MFMA requires the general contractor to provide a concrete slab troweled smooth and flat to a tolerance of 1/8" in a 10' radius, subject to the approval of the FSF wood flooring contractor.

 

Labor and materials necessary to put the concrete slab in acceptable condition, (high areas ground down and low areas filled with appropriate leveling compounds) are the responsibility of the general contractor or concrete subcontractor.

 

No pea gravel, river gravel or slag aggregate can be allowed in a gymnasium concrete slab. The concrete strength range at the time of wood flooring installation should be between 3,000 P.S.I. and 3,500 P.S.I.

FSF recommends the following procedures to be used by the general contractor or concrete subcontractor to provide the appropriate slab flatness requirement:

 

  • Plot a 5' grid on the slab surface.

 

  • Using a 10' straight edge, move it perpendicular to the plotted grid in both directions to identify all areas requiring correction. (Note: The use of a transit or laser alone does not include measurements between the grid points.)

 

  • All high spots should be ground level. Fill low areas with appropriate leveling compound. The fill must not become brittle, crack or lose bonding to the concrete slab. Fill must not be affected by loads applied to resilient pads if present. In anchored system applications, the fill must provide the required P.S.I. strength and allow anchoring without breaking or spawling when pins are installed. This is the responsibility of the general contractor or concrete subcontractor.

CONCRETE SLAB MOISTURE CONTENT

Installation of an MFMA flooring system shall not commence until the subfloor is determined to be "dry" by industry standard testing procedures. MFMA does not recommend testing for concrete moisture content within 60 days of pour. The required vapor barrier or under-slab membrane will likely increase slab drying times. Some factors affecting the concrete slab ‘s drying time include:

 

  • Slab thickness

  • Surface applied treatments

  • Type of construction

  • Concrete formulation

  • Location of the building

  • Climatic conditions

  • Power troweling

 

When conducting slab moisture testing, follow the manufacturer’s recommendation on the number of tests that should be performed - regardless of the age of the slab, document all tests. If the test(s) indicate a wet slab, delay installations of the maple system until specified conditions are met.

 

It is the general contractors’ responsibility to provide a dry concrete slab within MFMA standards for moisture content and flatness. The flooring contractor shall verify slab conditions prior to the commencement of any maple flooring system installation to ensure compliance with flooring manufacturer specifications.

 

The only MFMA recognized method for reading concrete moisture levels within a slab is by testing its relative humidity. Please refer to the instructions of the manufacturer’s relative humidity test kit for complete details on how to administer the test correctly. MFMA recommends the relative humidity level for a concrete slab for anon-glue-down maple floor system be 85% or lower and for glue down systems the concrete slab relative humidity level should be 75% or lower before installation. For concrete relative humidity conditions above MFMA’s recommendation consult your FSF Sport Floor Contractor.

 

Concrete Relative Humidity Test

  • Relative Humidity Test (In-Situ Probe Test)Use a prepackaged relative humidity testing kit (must be compliant with the most recent ASTM F2170) and follow the manufacturer's instructions. This test method involves measuring relative humidity levels inside of the concrete slab.

 

Pre-Tests

The following can be administered as pre-tests for testing the moisture content of a concrete slab but should not be used to confirm a concrete slab has dried to acceptable levels:

  • Polyethylene Film TestTape a 2' x 2' square of 6 mil clear polyethylene film flat to the slab, sealing all edges with moisture resistant tape. Suspend a 250-375 watt heat lamp 2' above the plastic film. After 24 hours, check the film - if no condensation or "clouding" develops on the underside of the polyethylene, the test area shall be considered dry enough to test the concrete slab’s relative humidity.

  • Calcium Chloride TestUse a prepackaged calcium chloride test (widely available) and follow the manufacturer's instructions. The Calcium Chloride Test measures the quantity of moisture passing through a concrete floor. This measurement is stated as pounds of moisture over a 1,000 sq. ft. area during a 24-hour period. An acceptable level is 4.5 lbs. or less.

  • Electronic Concrete Moisture MetersDue to the different types of electronic concrete moisture meters on the market, MFMA recommends following the manufacturer’s instructions for proper on-site testing procedures.

CUPPING AND CROWNING

Cupping and crowning are two unfortunate results of excessive moisture in maple flooring.

 

All moisture content increases cause wood products to expand. Due to the cellular structure of flat-sawn maple flooring, expansion takes place primarily across the width of each strip. When flooring strips in a maple system take on enough moisture to expand and eliminate all available horizontal expansion space, individual boards will expand upward at the edges causing the surface condition commonly known as cupping. Cupping is caused by a moisture imbalance through the thickness of the maple — moisture contents in each strip of flooring are higher at the bottom than on the surface.

 

If cupping is severe enough, a condition known as "compression set" can occur. Compression set is caused by severe expansion pressure from excessive moisture causing individual boards to crush each other. Individual cells on the edges of each maple strip are permanently deformed or crushed, leaving excessive cracks and ragged edges when the material returns to its normal moisture content.

 

Crowning is the opposite of cupping. The center of each flooring strip is higher than its edges. Moisture imbalance is sometimes the cause of crowning if excessive moisture is introduced on the top of the floor due to roof leaks, spills or improper maintenance procedures. However, crowning is more commonly caused by sanding a cupped floor before the moisture content in the maple returns to a uniform and normal condition top to bottom.

 

Sanding while the flooring is still cupped will result in the loss of flooring material on the edges of each board. Once all excess moisture works its way out of the flooring materials, the maple will return to a flat condition - except where the original edges of the strips were sanded off, leaving voids at the edges of each flooring row.

 

Some slight cupping and/or crowning may occur naturally and is acceptable. The "bark" side of a maple log will shrink/swell more than the center of a maple log, and this minor expansion/contraction variation is more noticeable in areas of the country that experience significant seasonal moisture content changes and on floors containing wider face-width maple strips.

 

MFMA recommends maintaining indoor temperatures between 55 and 75 degrees and indoor relative humidities between 35 percent and 50 percent year round. If the flooring materials are properly acclimated, a 15 percent fluctuation in indoor relative humidity will not adversely affect the maple. Excessive shrinkage and/or expansion may occur with indoor relative humidity variations in excess of 15 percent.

DEAD SPOTS

Cupping and crowning are two unfortunate results of excessive moisture in maple flooring.

 

All moisture content increases cause wood products to expand. Due to the cellular structure of flat-sawn maple flooring, expansion takes place primarily across the width of each strip. When flooring strips in a maple system take on enough moisture to expand and eliminate all available horizontal expansion space, individual boards will expand upward at the edges causing the surface condition commonly known as cupping. Cupping is caused by a moisture imbalance through the thickness of the maple — moisture contents in each strip of flooring are higher at the bottom than on the surface.

 

If cupping is severe enough, a condition known as "compression set" can occur. Compression set is caused by severe expansion pressure from excessive moisture causing individual boards to crush each other. Individual cells on the edges of each maple strip are permanently deformed or crushed, leaving excessive cracks and ragged edges when the material returns to its normal moisture content.

 

Crowning is the opposite of cupping. The center of each flooring strip is higher than its edges. Moisture imbalance is sometimes the cause of crowning if excessive moisture is introduced on the top of the floor due to roof leaks, spills or improper maintenance procedures. However, crowning is more commonly caused by sanding a cupped floor before the moisture content in the maple returns to a uniform and normal condition top to bottom.

 

Sanding while the flooring is still cupped will result in the loss of flooring material on the edges of each board. Once all excess moisture works its way out of the flooring materials, the maple will return to a flat condition - except where the original edges of the strips were sanded off, leaving voids at the edges of each flooring row.

 

Some slight cupping and/or crowning may occur naturally and is acceptable. The "bark" side of a maple log will shrink/swell more than the center of a maple log, and this minor expansion/contraction variation is more noticeable in areas of the country that experience significant seasonal moisture content changes and on floors containing wider face-width maple strips.

 

MFMA recommends maintaining indoor temperatures between 55 and 75 degrees and indoor relative humidities between 35 percent and 50 percent year round. If the flooring materials are properly acclimated, a 15 percent fluctuation in indoor relative humidity will not adversely affect the maple. Excessive shrinkage and/or expansion may occur with indoor relative humidity variations in excess of 15 percent.

END JOINT SPACING IN RANDOM LENGTH STRIP AND FINGER JOINED STRIP FLOORS

End joints are the locations on a random length or finger-jointed strip wood floor where two pieces of flooring are joined together end to end by a single tongue and groove. Segment joints are the locations on a finger-jointed wood strip floor where two pieces of flooring are joined together end to end by a finger-joint. End joint spacing serves a very important structural function in athletic flooring systems that have non-continuous subfloor designs. Examples of such designs are "Sleeper" and "Fixed Sleeper" flooring systems without continuous subfloors. When end joints are installed closely together in adjoining rows, such concentrations of end joints can create weak spots in the system construction. MFMA recommends maintaining a minimum of 4 inches between end joints in adjoining rows when non-continuous subfloor designs are specified for athletic flooring installations.

 

End joint spacing does not serve a significant structural function in athletic flooring systems with continuous subfloor designs. However, proper spacing of end joints in adjoining rows of a maple athletic flooring system is important in order to maintain consistent performance characteristics across the playing surface. For this reason, MFMA also recommends maintaining the traditional minimum of 4 inches between end joints in adjoining rows when continuous subfloor designs are specified for athletic flooring installations.

 

Given the above recommendations, MFMA acknowledges that even the most conscientious installer may occasionally install flooring strips with end joints spaced less than 4 inches in adjoining rows on a typical flooring installation. Such occasional installation is by itself not a valid reason for rejection of an athletic flooring surface.

 
 
 
 
 
 
 
 
 

EXPANSION SPACING ("WASHER ROWS")

Wood is a hygroscopic material. When exposed to varying temperature and humidities, it will release or absorb moisture until it is at equilibrium with the surrounding atmosphere.

 

Maple floors in the United States experience moderate seasonal moisture content swings as a result of normal climate changes during the year. For example, in an average year, maple flooring in lower Michigan experiences a 3 percent to 4 percent variation in moisture content, depending on location. A 4 percent swing can translate just less than 1/32" of expansion/contraction for each 2 1/4" face-width board in a maple flooring system.

 

To ensure successful placement and performance, many contractors install intermediate expansion spaces at regular intervals across the surface to allow maple expansion as normal seasonal changes dictate. Intermediate expansion spacing (or "washer rows") is installed at the discretion of the flooring contractor based on flooring moisture contents at the time of installation and/or normal anticipated changes in moisture contents throughout the year. Although either 1/16" or 1/8" washers are commonly used, the 1/16" spacers require less movement of the flooring strips during expansion, and are less visually objectionable.

 

Please note that spacing and frequency of intermediate expansion spacing is directly related to the time of year that the flooring is installed, as well as the amount of acclimation time provided in the construction schedule. Until you have a firm construction timetable from the General Contractor, it is difficult to calculate the precise amount of expansion/contraction spacing that will need to be provided.

EXPANSION VOIDS

Expansion voids are areas in a maple sports flooring system where no flooring or subflooring components are installed, specifically to provide space for system movement. Expansion voids are usually found at the perimeter of a floor and at all vertical obstructions (bleacher anchors, volleyball inserts, floor electrical outlets and audio box hookups, etc.) within the borders of the floor.

 

Fosters' sports flooring systems are generally designed in either "fixed" or "floating" configurations. "Fixed" flooring systems are typically specified in locations where system movement is not anticipated or desired, and "floating" floor systems are typically specified in installations where system movement is anticipated.

 

All MFMA manufacturers have detailed specifications which call for installation of expansion voids at the perimeter and at all vertical obstructions on certain of their flooring systems. The installation of expansion voids at the system perimeter and at all vertical obstructions is required in most "floating" floor system specifications.

 

As a general rule, FSF recommends that no fixtures, equipment or bleachers be anchored through "floating" maple sports flooring systems into the concrete subfloor without first cutting surface maple and wood subfloor components away from lag bases and permanent in-floor fixtures to provide proper space for normal system movement.

 

"Fixed" systems such as the generic Nail-in-Channel and Channel and Clip floors are designed to hold the flooring tightly in place, restraining the system from movement. Installation of expansion voids at the perimeter and at vertical obstructions is not usually required with these system configurations.

Consistent effort must be given to keep all expansion voids clean and free of debris. Regular attention to perimeter voids and floor insert locations will ensure flooring system movement as the system was designed. Buckling, warping and rolling of flooring components can occur when expansion voids are clogged with debris — impeding the system from free movement it was designed to accommodate.

MFMA and all of its member manufacturers have published specifications that prescribe optimum temperature and humidity ranges to ensure satisfactory performance and reduce the likelihood that any bind-up of components will ever occur on a maple floor installed with proper provision for system movement.

 

FSF recommends maintaining indoor temperatures between 55 and 75 degrees and indoor relative humidities between 35 percent and 50 percent year round. If the flooring materials are properly acclimated, a 15 percent fluctuation in indoor relative humidity will not adversely affect the maple. Excessive shrinkage and/or expansion may occur with indoor relative humidity variations in excess of 15 percent, and variations of this magnitude may create difficulties with vertical obstructions in some "floating" flooring systems.

 
 

Ff/Fl NUMBERS AND CONCRETE SLAB FLATNESS

The American Concrete Institute has adopted F-Numbers as its standard for the specification and measurement of concrete slab flatness and levelness.

 

Ff, or "flatness F-Number," defines the maximum floor curvature allowed over 24" (600 mm) computed on the basis of successive 12" (300 mm) elevation differentials. Fl, or "levelness F-Number," defines the relative conformity of the floor surface to a horizontal plane as measured over a 10' (3.03m) distance. The higher the F-Numbers, the more level or flat the slab.

 

MFMA does not acknowledge the use of F-Numbers to measure levelness/flatness tolerances in gymnasium slab applications. If an F-Number is specified for flatness, it must be at least the equivalent of MFMA's standard 1/8" in 10' radius tolerance, and the following conditions must be adhered to in order to meet MFMA's standard slab specification:
 

  • The F-Number measurement must be taken two (2) weeks prior to the maple floor installation.

  • The measurement process must include all construction joints over the entire concrete slab.

  • The FSF flooring installer must be present during the entire measurement process.

 

If the above conditions are not met during all Ff/Fl Number measurements, MFMA does not recommend the acceptance of any Ff/Fl test. MFMA's standard 1/8" in 10' radius flatness specification should be enforced.

 
 

FINISH AMBERING

Urethane oil finishes (the type most commonly specified for maple basketball, multipurpose and stage floors) as a group have a tendency to amber over time. The timing and degree of the ambering vary by product, but typically the greatest color change in the finish takes place between the sixth month and the end of the first full year of service.

 

In a repair situation, replacement boards will appear generally lighter in color than surrounding existing boards due to the ambering affect of the existing oil finish. The degree of variance is a function of the age and number of coats of finish on the original flooring. Color variations in the finish should be expected on a repaired floor immediately after repairs are completed. Most repair areas begin to blend in with surrounding flooring after several months and over time become imperceptible to the untrained eye.  As a rule MFMA does not recommend tinting a repaired area to match existing floor coloring, and does not recommend staining maple flooring under any circumstances.

FINISH PEELING/CHIPPING

Finish peeling and/or chipping, in a very moderate form, occasionally occurs in new maple installations that experience large swings in humidity levels. This condition most often develops over painted areas of the maple surface.

 

MFMA has no written policy or specification regarding the appearance or frequency of finish peeling and/or chipping in MFMA flooring installations. Finish peeling and/or chipping can be a result of expansion/contraction of the flooring system due to seasonal moisture level changes, which causes fractures in the finish in painted areas as maple flooring adjusts to drier indoor conditions during the heating season.

 

The "elastic" properties of many surface finishes are commonly restricted by application over less "elastic" game line paints. During the first heating season, a new maple floor will typically contract more than in subsequent years under the same environmental conditions. USDA performance data confirms this physical characteristic with all hardwood species.

Assuming drier than average conditions exist in a facility during the first heating season, above-average shrinkage may result in some pai