Monday, August 19, 2013

Oriented Strand Board (OSB)


    OSB is made of thin narrow strands of hardwoods and softwoods that are longer than they are wide. The strands are dried, screened, blended with adhesive and formed into a multilayered mat. In the surface layer, the long axes of the strands are oriented so that they are, in general, parallel with the long direction of the panel. The strands in the inner layers may not be oriented in any particular direction or may be generally oriented perpendicular to the long direction of the panel.


  1. APA Trademarked Plywood or Equivalent Agency Certified Plywood rated as suitable underlayment for resilient floor coverings such as tile or sheet vinyl. It should have an Exterior or Exposure 1 exposure durability classification and a fully sanded face. APA plywood underlayment grades recommended for areas to be covered with resilient non-textile flooring are A-C, B-C, C-C Plugged or C-C Plugged EXT when marked “sanded face.” Also, Marine EXT or sanded plywood grades (A-C, B-C, A-D or B-D) marked “Plugged Crossbands Under Face,” “Plugged Crossbands (or Core),” “Plugged Inner Plies” or “Meets Underlayment Requirements.”
  2. Poplar or Birch Plywood with a fully sanded face and exterior glue.
  3. Lauan Plywood, when used as an underlayment, should be Type 1 (Exterior). The best grade is BB and the next best is CC, while OVL (overlay grade) is the minimum acceptable face grade. There is a wide variety of quality and species classed as lauan. Some may present severe problems such as discoloration, indentation, loss of bond and delamination when used as an underlayment.
  4. Treated Plywood- Armstrong resilient flooring is not recommended directly over fire-retardant treated plywood or preservative treated plywood. The materials used to treat the plywood may cause problems with adhesive bonding. An additional layer of at least 1/4" thick underlayment should be installed for the construction to still meet the applicable building or fire codes.

b) Hardboard
    Untempered hardboard which meets requirements for wood underlayments is acceptable only for use under Armstrong resilient flooring products installed by the Residential Felt-Back perimeter bond method.

d) Particleboard
    Particleboard, often called “chipboard,” is comprised of small particles usually arranged in layers by size, but not oriented. Composite Panel Association- approved grades of particleboard underlayment are acceptable only for use under Armstrong resilient flooring installed by the Residential Felt-Back perimeter bond method.

e) Fiber Reinforced Gypsum Underlayment, Fiber Cement Board and Cementitious Backerboard
    These products must be designed specifically for vinyl floor coverings. Written installation instructions and a guarantee for the product’s use in conjunction with vinyl floor coverings should be furnished by the manufacturer.

f) Wood Subfloors with Concrete or Gypsum Toppings
    These subfloors consist of lightweight concrete or gypsum-based topping over plywood on wood joists or trusses. See Concrete

Note: Regardless of the type of underlayment used under Armstrong resilient flooring, the responsibility for warranties and/or performance guarantees for the underlayment rests solely with the underlayment manufacturer and/or supplier and not with Armstrong. The types of subfloors and underlayment panels described in this manual (F-5061) are intended only as a guide and should not be construed as an Armstrong warranty for these products. Armstrong cannot be responsible for:
  • joint or texture show-through
  • tunneling and ridging over underlayment joints
  • discoloration from stain sources in the panel, regardless of the type of underlayment panel used
    • underlayment panel problems caused by local climate conditions, basement wall and subfloor construction or improper installation

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