VA. Tech Study on OSB and PLYWOOD Panels.
Va. Tech - Dr. J. Lofersky's Study on OSB and PLYWOOD FOR WOOD FLOORING PROFESSIONALS.
Years ago, a study was done on the nail withdraw strength of OSB and PLYWOOD using staples and cleats at Va.Tech by Dr. Joesph Loferski.
The results are still pertinent today and Dr. Loferski has periodically updated his research on OSB and PLYWOOD Panels.
Below is a copy of that study.
Years ago, a study was done on the nail withdraw strength of OSB and PLYWOOD using staples and cleats at Va.Tech by Dr. Joesph Loferski.
That is 28 plus years of research for the flooring industry as researchers and consultants for the wood flooring industry. A lifetime of service that cannot be matched in our wood flooring trade.
VIRGINIA TECH SUBFLOOR TEST REPORT
Included is the official summary, plus excerpts from significant charts, from the above research project officially entitled: “Performance of Wood Floor Systems Under Fluctuating Moisture Changes.
The project was conducted by the Department of Wood Science and Forest Products at Virginia Tech, and was commissioned by NOFMA, with the help of four co-sponsors to determine in part: The best fastening system for nail-down hardwood floors over commonly used subfloor materials under realistic construction-site and occupational weather/moisture conditions.
This statement captures the essence of the test report, and we commend the Virginia Tech team of Drs. Lang, McLain, and Loferski for their thorough two-year testing techniques.
They found that hoards make the best subfloors in terms of nail- holding ability, and the thicker panels, 5/8” (19/32”) and 3/4” (23/32”) plywood and 3/4” (23/32”) OSB, act comparably.
Other highlights of the report embody some surprising -- and not-so-surprising -- findings. -
Polyurethane finish on a wood floor tends to reduce the size and number of cracks. (This does not address ‘Panelizing” caused by the edge-gluing characteristics of some urethanes)
Manual nailing with machine driven cleats (as opposed to pneumatic stapling) is more consistently strong.
Pneumatic driven fasteners often leave damaged tongues with negligible holding power. -
When installed floors have been cycled through a low-to-high-to low Moisture Content, flooring tends to return to the original position with plywood subfloors.
After similar cycles flooring tends to remain out original position with OSB so more permanent gaps can be expected.
Staples have the highest holding power, but are inconsistent due to damaged tongues.
The statistics indicate the fastener holding strength between staples and nails through 2 or 3 moisture cycles narrows significantly and shows little difference. -
After 2 1/2 years of simulated moisture cycles 5/8’ (19/32’) and 3/4’ (23/32”) plywood and 3/4’ (23/32”) OSB subfloors were comparable in nail holding power. - Board subfloors had the highest nail holding power.
Chart for Mean Withdraw Strength (see above chart)
SUMMARY
Eight floor systems, constructed using seven subfloor materials, two fastener types, and two finishes, were subjected to an accelerated schedule of service environments.
Subfloor variables included diagonal southern pine boards, three thickness of plywood and three thicknesses of OSB.
One type of nail and one staple were used to fasten sections of each floor; a polyurethane and sander-sealant finish were used.
The environmental schedule was designed to simulate the expected conditions experienced by floors in the first two and one-half years of service.
The analyses of the results led to the following results and conclusions.
DIMENSIONAL CHANGES
The response of the floor system to cyclic moisture content changes was measured by the horizontal movement of 10 flooring strips located in different sections of the floors. Individual floor strips were measured for width and thickness changes.
The horizontal distance change results are inconclusive with respect to most study variables. It does appear, however, that the plywood subfloors allowed more lateral movement in the flooring than did the OSB subfloors,
This difference may be due to any difference in the moisture expansion coefficients of the composite products or to the differences in actual moisture content at equilibrium.
No significant effect of the study variables were observed on any changes in thickness and width of individual strips.
The principal factor influencing strip dimensions was the ring angle position of the strips.
FASTENER STRENGTH RETENTION
The fastener withdrawal strength of the subfloor-flooring connection was determined using the methods of ASTM D 1037-91.
The withdrawal strength from the subfloor was tested at various exposure stages on specimens taken from the test floors.
The principal findings regarding fastener strength retention in subfloors are:
a) The nail and staple connections to the SYP board subfloor, with high initial strength and minimum strength loss, outperformed the connections in all other subfloors.
b) Staple connection strength was, in general, slightly higher than nailed connection strength for the test fasteners
However, because of installation damage, staple connections are less reliable and consistent than nailed connections for flooring.
Pneumatic stapling resulted in damage to the tongue of flooring which resulted in negligible strength for some stapled connections.
c) Initial connection strength is greater for nails and staples in plywood as compared to OSB in comparable thicknesses. Thickness of OSB had less influence on initial withdrawal strength than did plywood thickness.
d) After two years of simulated service, the residual strength of fasteners in 19/32 inch and 23/32 inch plywood and 23/32 inch OSB were comparable.
FLOOR QUALITY
Floor quality was assessed at the different exposure stages by measuring gaps between strips, a floor surface profile, and visual evaluation of localized defects.
Gap ratio is defined as the area of measured gaps in square inches divided by the area of the floor section measured by square yards.
The following observations were made:
a) The type of finish on the floor had the greatest influence on floor quality, as measured by gap ration, compared to the other study variables of subfloor type/thickness and fastener type.
Polyurethane (PU) finish consistently slowed moisture migration through floors compared to the sander-sealant (SE) finish.
This resulted in steeper moisture gradients in flooring under PU finish than under the SE finish.
Because of the moisture retarding effect, gaps in PU finished flooring are less likely to form as a result of relatively short term changes in environmental conditions.
b) Based on a subjective assessment of the measured surface profiles of the study floors, after a drying cycle from 12% MC to 6% MC, there were fewer occurrences of cupping in individual strips under the polyurethane finish than under the sander- sealant finish.
However, there were less global deviations from a horizontal base line in groups of strips under the sander-sealant finish than under polyurethane finish.
c) With respect to the floor profiles measured at the final exposure stage, the performance of subfloor materials in decreasing order of floor quality were SYP, plywood, and 0SB.
d) The frequency of localized defects, such as edge crushing, is more a function of the anatomical characteristics of individual strips than of any of the study variables.
e) Protection of subfloor materials from weather, before installation of oak strip flooring, results in significantly greater floor quality than if protection is not afforded.
CONCLUSIONS AND OPINIONS
Based on observations of the eight study floor systems subjected to a simulated two-year exposure, in general, oak strip flooring on SYP board subfloors results in the highest standard of floor performance and the floors on 1/2 inch OSB results in the lowest performance.
It is our opinion, that good floor performance can be expected with 19/32 inch or thicker plywood or with 23/32 inch OSB subfloors
Mechanical nailing results in a more consistently strong connection than pneumatic gun stapling of floor strips. Finishes which are more effective at retarding moisture movement than the sander-sealant, can be expected to result in the best floor performance under changing MC conditions.
The lack of protection of subflooring from weathering, before the installation of oak flooring, significantly reduces floor quality. This research was initiated by NOFMA:
The Wood Flooring Manufacturers Association for the benefit of the flooring industry.
Below you will find a list of contributors.
NOTE: Check with the manufacturer of the flooring to be installed for their acceptance of OSB as a subfloor material.
CONTRIBUTORS TO THIS RESEARCH:
NOFMA: The Wood Flooring Manufacturers Association
Maple Flooring Manufacturers Association
National Wood Flooring Association 233 Old Meramec Stn Rd Manchester, MO 6
Powernail Company
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