USG Fiberock Underlayment and Tile Backerboard - Manual (Page 5)

Preparation
Crawl-Space Requirements
Crawl-space requirements may
vary based on geographic location.
Consult local building codes for
more specific information regarding
vapor barriers and their uses.
Subfloor Requirements
The subfloor system should
be designed for a deflection
limit of L/360 for the span. The
subfloor should be APA Span-
Rated Plywood or OSB with
an Exposure 1 classification
or better with tongue and
groove or back-blocked at the
unsupported edges.
Resilient Flooring
Joist
Minimum
Spacing Subfloor
Thickness
16", 19.2" 23/32"
and 24" o.c.
Ceramic Tile
Joist
Minimum
Spacing Subfloor
Thickness
16" o.c. 19/32"
19.2" o.c. 23/32"
24" o.c. 23/32"
Wood Subfloor
sand uneven
joints
fill and
sand gaps
flush with or slightly
below surface
Clean subfloor and leave free
of dust, dirt and debris. Ensure
that subfloor is completely dry
(no more than 12% moisture
in subfloor prior to installation).
Verify that fasteners are flush
with, or slightly below, subfloor
surface.
Ensure that subfloor and
structure are within tolerances
specified by floor covering
manufacturer. Inspect subfloor
for even, flat surface before
installing underlayment.
Uneven end edge joints and
variations in subfloor panel
thickness may telegraph
through underlayment in vinyl
applications. Sand uneven
joints, if necessary.
Ensure that subfloor is
flat between framing elements.
If subfloor panels appear to
buckle, correct by adding
blocking or cleats under floor.
Fasten cleats to subfloor to
flatten panels. Repair voids, large
gaps and penetrations through
subfloor using a manufacturer-
approved floor leveler prior to
installing F
iberock
underlayment.
Over Existing Vinyl Floor
CAUTION: Do not install F
iberock
underlayment over heavily
cushioned, thick foam-backed
floor coverings.
– Ensure that existing floor is
level and meets appropriate
design requirements.
– Repair any missing or broken
vinyl tiles, curling seams,
severe gouges, or protrusions
by filling with floor leveler.
If floor will be finished with
ceramic tile, make sure that the
existing vinyl covering is fully
adhered and bonded to the floor.
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