SpecTech January 2014
Guidelines for Successful Tilt-Up Utilizing a Casting Bed or Stack Cast Panels MORE AND MORE TILT-UP PROJECTS ARE UTILIZING SEPARATE OR TEMPORARY CASTING SLABS (WASTE SLABS) OR STACK PANELS. THESE SLABS ALLOW GREATER FLEXIBILITY IN PANEL DESIGN AND LAYOUT. SPECIAL ATTENTION NEEDS TO BE TAKEN WITH THIS TYPE OF CASTING SURFACE TO ASSURE A CLEAN, SUCCESSFUL TILT. KEY PARAMETERS: 1. Mix Design - Avoid pozzolans (flyash, slag) to allow a tight finish and maximum strength gain. Casting beds with straight Portland cement create a better reaction with the bondbreaker which results in less bondbreaker required to achieve “hold-out.” 2. Minimum Thickness - Larger panels will require a greater mass (thickness) to counteract a potential suction. A reinforced, casting bed with a minimum 3.5”-4.0” thickness will provide enough mass to allow hard trowelling a dense, less porous surface. Proper sub grade preparation is also critical to maintain uniform slab thickness (i.e. truck ruts). 3. Surface Finish - Since some of these casting beds are temporary, and not finished or cured to the same degree as the interior floor slab, extra time and attention needs to be spent creating a tight, dense, hard trowelled surface. 4. Proper Curing - Must be cured immediately (not next day) and with the same quality cure as the main floor slab. Maintaining the moisture in the slab and using the moisture to keep the bondbreaker on the top of the slab is critical. 5. Bondbreaker - Suggest doubling bondbreaker application as a precaution when using temporary casting slabs and stack cast panels.
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