PRECON Shotcrete Technical Bulletin

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PRECON SHOTCRETE TECHNICAL BULLETIN: PRE-APPLIED/UNDERSLAB WATERPROOFING SYSTEM

Shotcrete is utilized in lieu of conventional concrete in many instances to meet project demands. The PRECON waterproofing system from W. R. MEADOWS is uniquely designed to function and perform with cast-in-place and shotcrete applications. As with any application, care should be taken to maintain the waterproofing membranes/systems integrity throughout the construction process.

Establishing a stable and firm foundation is crucial to prevent any shifting or displacement of the PRECON system during the application of shotcrete. Prior to shotcrete construction commencing, it is advised preconstruction testing and mock-up of PRECON and shotcrete assembly be constructed for evaluation as per project specific requirements.

Prior to full-scale shotcrete placement, inspect all areas of installed PRECON system for damage and to ensure all PRECON system components have been installed per W. R. MEADOWS guidelines and specifications.

Shotcrete must be placed in accordance with ACI 506.2 “Specification for Shotcrete.” As stated in ACI 506R-16, “A successful project is dependent on not only an experienced nozzleman, but an experienced contractor and shotcrete crew.” Shotcrete construction and quality assurance/quality control are crucial elements for a successful shotcrete application over the PRECON system.

Due to its unique composition, shotcrete is susceptible to shrinkage cracks, with potential problems arising from suboptimal workmanship, including voids between overspray, excessive rebounding, formation of the shotcrete and the waterproofing membrane, or what is referred to as “shadow voids” behind steel reinforcement. Improperly mixed or porous shotcrete can also pose concerns.

SUCCESSFUL APPLICATIONS OF SHOTCRETE OVER PRECON INCLUDE BUT ARE NOT LIMITED TO THE FOLLOWING:

• Installation of shotcrete within 56 days (42 days in hot climates) ACI 506.2-95
• Protection of PRECON membrane from shotcrete overspray during application. This can be accomplished by lightly taping a piece of polyethylene plastic sheeting or similar temporary protective product.
• Confirming all shotcrete wall assembly components (forms, rebar, dowels, rods, etc.) are not interfering with the PRECON fabric to make full and continuous contact with shotcrete during installation.
• Avoid the use of sharp items for consolidating shotcrete.
• Maintaining the integrity of PRECON vertical seams (selvedge edge) during shotcrete This can be accomplished by applying a “straight pattern” of shotcrete in these locations, avoiding spraying directly into the “open” edge of the overlap in advance of “circular” patterns. Should the above means and methods be unable to be employed, the use of HYDRALASTIC_™ 836 membrane and DETAIL FABRIC from W. R. MEADOWS in these vertical seams (selvedge edge) locations may be required. Contact your local W. R. MEADOWS’ representative for further information.

PRECON waterproofing system will continue to perform and excel with the use of shotcrete applications.

2025-02