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�'. <br /> �y Mr. Charles Thompson <br /> Project BL-04-05907 <br /> � October 27,2004 <br /> Page 8 <br /> a <br /> � <br /> i C.S.d. Seepage Control. If basements or below-grade parking are built, as a precaution against <br /> � basement seepage, we recommend the walls be adequately dampproofed and installing a perimeter <br /> � foundation drain system. The drain tile system should include a perforated pipe with an invert within 2 <br /> inches of bottom-of-footing elevation. Collected seepage should be routed to a sump and then drained by <br /> � a pump or gravity to a storm sewer or low area on the site. <br /> � <br /> C.6. Floor <br /> � <br /> � C.6.a. Subgrade. After the building pad preparation has been completed,we anticipate the floor <br /> ■ subgrade will be sandy alluvial soils or engineered fill. These soils should be directly suitable for floor <br /> slab support. Backfill in footing and mechanical trenches should be compacted to a minimum of 95 <br /> a percent of its standard Proctor maximum dry density within 3 percentage points of its optimum moisture <br /> � content. <br /> � C.6.b. Vapor Barrier. Excess transmission of water vapor could cause floor dampness, certain types of <br /> � floor bonding agents to separate, or mold to form under floor coverings. We recommend placing a vapor <br /> retarder or barrier below the floor if coverings or coatings less permeable than concrete will be used,or if <br /> � moisture is a concern. <br /> � <br /> Current industry recommendations are to place the vapor retarder or barrier directly below the concrete. <br /> � It is then desirable to take precautions against shrinkage and curling of the floor slab. Industry practice . <br /> , has been to allow burying the vapor retarder or barrier below a layer of sand to reduce curling and <br /> shrinkage of the concrete,but this practice often traps water between the slabs and the vapor retarder or <br /> � barrier, causing problems after a period of months. In any case,we recommend consulting with floor <br /> � covering manufacturers regarding the appropriate type,use and installation of a vapor retarder or barrier <br /> to preserve warranty assurances. <br /> � . <br /> � To reduce shrinkage and curling processes associated with placing concrete directly on the vapor retarder <br /> � or barrier, we recommend: <br /> � • Using the largest possible maximum aggregate size and/or coarse aggregate. <br /> ■ • Using the lowest practical slump. <br /> • Using the lowest necessary cement content to reduce top-to-bottom moisture differentials. <br /> � • Carefully curing the concrete. <br />� , � Optimizing the spacing of control joints. <br /> • Cutting control joints as soon as practical. <br /> � <br /> , <br />