Subfloor Preparation
and Moisture Mitigation
“an ounce of prevention is worth a
pound of cure”
Benjamin Franklin
Outline

Concrete Slab Basics
 Moisture Sources and Testing Methodologies
 Repairing Defects in Concrete Surfaces
 Crack Repair Treatments
 Treatments for Moisture Vapor Emission
Concrete Basics

Cement
 Supplementary
Materials
 Aggregates
 Water
Moisture Sources

Water of Hydration

Water required to complete chemical reaction
• Typically considered ~25% of cement by weight

Water of Convenience

Water used for ease of workability and placement
• Usually another 25% to 40% of cement by weight

Moisture Vapor Transmission (MVT)

Water of convenience evaporating
• 4” slab poured at .50 W/C evaporates >½ gallon per sq ft.

Water coming up through the concrete from under slab
Water in the Slab

Free water


This water is found within
the capillaries of the slab
and will begin to evaporate
if given the correct
conditions.
Bound water

This is the water that is
permanently bound as an
integral part of the concrete
slab.
Concrete Curing/Drying

All concrete requires
time to “dry”.

4” concrete slab with a
0.5 w/c ratio over an
impermeable moisture
barrier will take
approximately 92 days
to get to a suitable
level for wood floor
installation
Reference: “Are your slabs dry enough for floor coverings?”
By Bruce Suprenant and Ward R. Malisch, Copyright 1998
Drying of Concrete

Thickness of concrete
slab also impacts
drying time
Open or Closed System

Open system: Slab in contact with earth



Greater opportunity for introduction of water post construction.
It is prudent to consider any slab of age to be an open system.
(compromised closed system design)
Closed System: Slab separated with a vapor “barrier”


Recommended within ASTM F710
Greater protection from introduction of water post construction,
but not bullet proof and often times not constructed according to
ASTM F710.
Basic Concrete Slab Construction

Site evaluation




Moisture barrier
specifications


Compressed soil
Large aggregate (capillary
break)
Smaller aggregate
0.010” thick reinforced film
Exterior Drainage and
Landscaping concerns
Closed System

A vapor barrier’s purpose from a
construction point of view differs
from the floor covering industry’s
and building occupier’s
perspective. Vapor barriers at the
time of slab pour are intended to
trap the necessary water required
for proper curing. Not an
adequate barrier for long term
protection from moisture
migration.
How Moisture Moves Through a
Slab

On grade concrete


Capillary & MVT
Below grade concrete

Capillary, MVT &
Hydrostatic Pressure
Moisture Testing per ASTM
Ravages of Moisture
7 Days of Extracted Moisture
20lb MVER
Amount of Moisture Extracted
MVE of 20 lbs./1,000 sq. ft. (9,07 kg per 92,9 m)/ 24 hours
Roughly 16 gallons of water over a 7 day
period over an area approximately 31’x31’
Flooring Moisture Issues
Solutions for Moisture Control

Silicate Penetrating Sealers
 Topical Sealers
 Epoxy Coatings
 Cementitious Overlay
 Single system approach (adhesive acts as
bonding agent and moisture control solution)
Penetrating Sealers





Penetrating type reactive sealers are liquid applied treatments that
chemically react with the concrete reducing the MVER.
There are also products that are incorporated into the product at the
time of pour. (mixed in the truck)
These may be silicate in nature (sodium, lithium, or potassium)
Some concrete mixtures will affect the efficacy of these types of
sealants in relation to moisture/ph suppression and bonding
compatibility with flooring adhesives.
Silicate type treatments are considered by some with much less
confidence than other topically applied products
Top Coat Sealers





Typically used for lower MVER/PH
conditions (approx. 8 lbs)
May not require slab surface
preparation depending upon
surface condition of the slab
Not typically recommended for
open slab systems.
May not be recommended for
below grade slabs.
Creates “non-porous” substrate
Epoxy Coatings






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There are single and multiple coat
systems available.
Designed for very high moisture/ph
conditions
Designed to reduce MVER to a
tolerable level at the bond line.
Isolates PH from flooring system.
Typical that slab must be abraded
through grinding or shot blasting.
Typical that a cementitious over lay is
required due to type of adhesive used
for the floor covering and/or repair
trenching caused by concrete surface
preparation.
May include a sand broadcast
Concrete Profiles for Epoxy
Membranes
Dual Function Adhesive Systems

New adhesive products designed
to seal the slab and act as a
bonding agent in one step.



Water based acrylic adhesive
Moisture cure urethane adhesive
Typically designed for a maximum
of 15lbs MVER and 90% RH
 May not be designed for certain
types of floor covering
 May or may not be recommended
for open slab systems or slabs
with hydrostatic pressure.
Dense Cementitious Overlay





Usually requires preparation of the slab’s surface
Primer is applied prior to top coat
Highly densified cementitious layer is poured (may be
self-leveling)
Floor patching as needed to bring to floor coverings
required levelness benchmark.
Isolates slab from floor covering system.
Slip Sheet Membranes





“Free floats” accommodating
minor cracks and joints.
Shot blasting or grinding is not
required.
Not necessarily compatible
with all flooring systems.
Effectively isolates floor
covering away from the slab
alleviating build up of vapor
pressure. (vapor moves
laterally)
PH resistant
Decisions Drivers and Pitfalls for
Moisture Solution Selection







Amount of remediation required (MVER and RH Levels)
Available funds (Moisture Issues not typically expected)
Incorrect system chosen for existing conditions / Lack of investigation.
Incomplete system that does not include accommodations for cracks or
joints.
System requires “certification” prior to purchase and application / Warranties
Liability/Support if failure occurs
Incorrect application or slab preparation
REPAIRING DEFECTS IN
CONCRETE SURFACES
Minor Defect Repairs





Cement Based with Liquid
Polymer Additives
Dry Polymer Modified Cement
based
Dry Polymer Modified Gypsum
based (residential and light
commercial use)
High hydrating, polymer and
fiber reinforced cement based
underlayments (skim coats)
Typical Usages: From Feather
egde to 1-1.5” Thickness in
single application
Use “exterior rated” patching
compounds on slabs with moisture
issues.
Large Area Repairs

Self Leveling
Underlayments




Prep
• Make sure the substrate has
the proper CSP or profile to
receive the leveler
Prime
• Select the right primer for the
substrate
Pour
• Follow all instructions on the
package
Wait 3 days for floor covering
installation
Deep Fill Repairs

Screeds


Typical fills up to 4”
thick
Cure time relatively
quick but reset the
clock in terms of
flooring acceptance as
much as 30 days
Concrete Profiles for Self Leveling
Underlayments
Crack Repair



Mechanically prepare control and
construction/expansion joints with a
diamond crack-chasing/concretecutting blade.
Overcut the joint width to obtain a
sound, clean edge.
Clean cracks or joints with oil free
compressed air and/or vacuum with a
dustless collection system to
completely remove contaminants
An Engineer or Consultant determines if
a crack is ‘dormant’ or ‘active’ and
which product to use
He who lives upon hope, dies fasting.
Benjamin Franklin