02-27-2002 Council Agenda - Laserfiche WebLink

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Mr. Sam Roberto Project BBXX- 01 -119A May 24, 2001 Page 9 D.4.b. Moisture Vapor Protection Excess transmission of water vapor could cause floor dampness, certain types of floor bonding agents to separate, or floor coverings to mildew. If floor coverings or coatings less permeable than concrete will be used, or if moisture is a concern, we recommend placing a vapor retarder or barrier below the slabs, Industry standards generally recommend burying the vapor retarder or barrier below a layer of sand to reduce curling and shrinkage of the concrete, but this practice risks trapping water between the slabs and the vapor retarder or barrier. In any case, we recommend consulting with floor covering manufacturers regarding the appropriate type, use and installation of a vapor retarder or barrier to preserve warranty assurances. If the vapor retarder or barrier is buried below a layer of sand, consideration should be given to: • Eliminating moisture- trapping slip sheets, where possible, from below the slabs. • Installing roof drains prior to retarder /barrier installation to reduce wetting of the sand cushion. • Directing the concrete subcontractor to keep excess process water away from the sand cushion. • Sealing control joints to discourage water from penetrating the slabs after construction. To reduce shrinkage and curling processes associated with placing concrete directly on the vapor retarder or barrier, we recommend: • Using the largest maximum aggregate size and /or coarse aggregate as possible. • Using the lowest practical slump and limiting the use of retempering water. • Using the lowest necessary cement content to reduce top -to- bottom moisture differentials. • Carefully curing the concrete. • Optimizing the spacing of control joints. • Cutting control joints as soon as practical.