Blindside Waterproofing – Pre-Applied/Underslab Membrane – PRECON

Pre-Applied/Underslab Waterproofing Membrane

PRECON is a composite sheet membrane comprised of a non-woven fabric, elastomeric membrane, and W. R. MEADOWS’ exclusive, patented plasmatic core (U.S. Patent No. 7,179,761).   The plasmatic core is a seven-layer matrix designed for toughness and provides the lowest water vapor transmission (WVT) rating on the market.  Once concrete is poured against PRECON and the concrete cures, a mechanical bond forms that secures the concrete to the membrane.

PRECON is used as a blindside membrane in vertical applications where access to the positive side is limited.  The membrane can also be used for horizontal applications for underslab waterproofing and vaporproofing.


  • Provides a waterproof seal between the membrane and poured concrete wall.
  • Helps prevent moisture migration into the structure.
  • Acts as a barrier against termites.
  • Reduces methane and radon gas intrusion.

4′ (1.2 m) wide x 50′ (15.2 m) long rolls, one roll per carton.

Store membrane cartons on pallets and cover if left outside. Keep materials away from sparks and flames.

ASTM E 1993-98*
*Standard Specification for Bituminous Water Vapor Retarders used in Contact with Soil or Granular Fill under Concrete Slabs.

Surface Preparation … Inspect all surfaces for any conditions detrimental to the proper completion of the work. Surfaces should be structurally sound. Remove debris or any other foreign material that could damage the membrane.

PRECON can be used with a caisson wall shoring system without the use of a drainage board. W. R. MEADOWS recommends proper site drainage, but due to certain site conditions this sometimes cannot be done effectively. The decision to remove the drainage board should be at the discretion of the engineer. In situations where a drainage board is not applied, surface preparation is important. The substrate needs to be sound, solid, and smooth.  Any gaps or voids >1″ (25 mm) need to be grouted.

Application Method … PRECON may be applied at temperatures down to 40° F (5° C); however, in less than ideal environments or marginal conditions, consider the use of PRECON LOW TEMP below 60° F (16° C). PRECON LOW TEMP can be used in temperatures down to 25° F (-4° C).MEL-PRIME™ from W. R. MEADOWS should be used to enhance the bond at the selvedge edge when conditions warrant with both PRECON and PRECON LOW TEMP.

Prior to application of the blindside membrane, attach MEL-DRAIN™ rolled matrix drainage system from W. R. MEADOWS to lagging or soil retention system.



Property Test Method PRECON Results
Color Black
Thickness ASTM D 1000 73 mil (1.85 mm)
Low Temp Flexibility ASTM D 1970, 180° @ -25° F (-32° C) Pass
Resistance to Hydrostatic Head ASTM D 5385-93 230′ (70 m)
Elongation, Polymeric Membrane ASTM D 412-06 > 400%
Tensile Strength, Film ASTM D 882 9200 psi (63.4 MPa)
Crack Cycling ASTM C 836 @ -15° F (-26° C) Pass
Puncture Resistance ASTM E 154 > 210 lb. (> 934 N)
Peel Adhesion to Concrete ASTM D 903 10 lb./in (1754 N/m)
Moisture Vapor Transmission ASTM E 96B 0.0011 perms
(0.0004 grains/ft.2/hr)
(0.007 gram/m2/24 hr)
Resistance to Penetration
by Termites
Texas A&M Method
Percentage of Penetration
Resistance to Penetration
by Pesticides
ASTM F 2130
Percentage of Penetration
Resistance to Fungi in Soil GSA-PBS 07115 – 16 Weeks No Effect

In vertical applications of PRECON, mechanically attach with fasteners every 12″ (31 cm) across the top, within ½” (13 mm) of the top edge of the membrane.  Install the membrane with the fabric side facing toward the concrete pour.

Remove release paper on 6″ (152.4 mm) overlap.  Apply membrane and roll press into place with a tile type roller.

End Laps … Overlap membrane 6″ (152.4 mm).  Prior to overlap, apply BEMHYDRALASTIC 836 or *MEL-ROL® LIQUID MEMBRANE (two-component) from W. R. MEADOWS in area to be lapped.  Roll press membrane into BEM, HYDRALASTIC 836 or MEL-ROL LIQUID MEMBRANE.  At terminations of membrane, apply BEM, HYDRALASTIC 836 or MEL-ROL LIQUID MEMBRANE 12″ (31 cm) wide centered over the termination and while still wet, embed 12″ (31 cm) wide DETAIL FABRIC into the HYDRALASTIC 836 or MEL-ROL LIQUID MEMBRANE and roll press into place.  Ensure that DETAIL FABRIC is centered over the termination with 6″ (15.2 cm) on each side of lap edge.  Apply additional HYDRALASTIC 836 on all terminations of DETAIL FABRIC.

Penetrations and Protrusions … Detail around all horizontal and vertical penetrations using BEM or MEL-ROL LIQUID MEMBRANE (two-component) from W. R. MEADOWS.   Apply BEM or MEL-ROL LIQUID MEMBRANE by forming a fillet around the pipe or protrusion, overlapping the fabric side of PRECON and the protrusion a minimum of 2.5″ (64 mm).  If the gap between the protrusion and the membrane is greater than ½” (13 mm), apply PRECON FABRIC TAPE over uncured BEM or MEL-ROL LIQUID MEMBRANE.  All penetration and protrusion surfaces must be clean, rust-free, and sound prior to application of BEM or MEL-ROL LIQUID MEMBRANE.

*MEL-ROL LIQUID MEMBRANE is a two-component material, not to be confused with MEL-ROL LM.

Patching … Prior to pouring, inspect membrane for punctures or damage and repair as necessary with HYDRALASTIC 836  and/or DETAIL FABRIC. (BEM or MEL-ROL LIQUID MEMBRANE may be used in place of HYDRALASTIC 836.)  In addition, ensure the membrane is free of standing water and has been cleaned of any deleterious materials that will affect the bond of the concrete to the membrane.

Underslab Application … Refer to ACI 302.1R-04: Chapter 4 – Site Preparation and Placing Environment for sub-grade preparation prior to PRECON placement.

Concrete should be poured within 60 days of membrane installation. For installations below 40° F (4° C), contact W. R. MEADOWS technical services.  When using bar supports, use those with a flat bottom.

May help contribute to LEED credits:

  • EA Credit 1: Optimize Energy Performance
  • IEQ Credit 3.1: Construction Indoor Air Quality Management Plan: During Construction
  • IEQ Credit 7.1: Thermal Comfort – Design
  • MR Credit 2: Construction Waste Management
  • MR Credit 5: Regional Materials

Mel-Rol Precon Overlap IllustrationPrecon Blindside Waterproofing

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