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Fwd: Re: Location of Vapor Barrier Below Concrete Slab on Grade[Subject Prev][Subject Next][Thread Prev][Thread Next]
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- Subject: Fwd: Re: Location of Vapor Barrier Below Concrete Slab on Grade
- From: rlewis(--nospam--at)techteam.org (Richard Lewis)
- Date: 30 Jul 1997 14:23:41 GMT
We typically see 2" sand over membrane over 2" sand in many soils reports. As I understand it, the 2" sand below the membrane serves as a capillary break with the membrane serving as imprevious moisture barrier. The sand below the membrane also helps to prevent punctures due to small rocks, etc. in the soil, especially if a layer of gravel is required below the sand (membrane over sand over gravel). The sand on top of the membrane serves to prevent punctures in the membrane from people walking on it and the wire chairs/adobe concrete blocks used to support the slab reinforcing. I have been told that sand helps with the slab curing and reducing curling since air can get in to the underside of the slab at the edges. But, you have to be carefull when placing the concrete on top so as not to get sand pockets in the slab. I would think the differential shrinkage across the slab is going to best be controlled by closely spaced control joints, which probably need to be cut in the slab as soon as you can walk on it (less than 24 hours after pouring). The mix design (low slump, low water/cement ratio) will obviously effect the shrinkage, and therefore cracking and permeability of the slab to moisture. My understanding is that you want to provide a capillary break under the slab to prevent moisture from moving upward, but this does not necessarily mean that it has to be a membrane. Since the floor manufacturer/installer will not warrent the work, it seems to me that you are stuck putting a membrane, especially since if you do not place the membrane and the floor covering buckles, then everyone is going to blame it on the lack of the membrane. By placing the sand over the membrane, I don't think you will have to be as concerned about the concrete mix design for the reasons that you listed (low slump, low water/cement ratio, etc.) since this will serve as an additonal capillary break. Question, If the flooring is so moisture sensitive, won't the installer also be sealing the concrete surface before installing the floor as added protection. Michael Cochran Brian L. Cochran Associates Los Angeles, CA -------------------------------- In a message dated 97-02-18 17:13:52 EST, you write: << Subj: Location of Vapor Barrier Below Concrete Slab on Grade Date: 97-02-18 17:13:52 EST From: Mcsherrygp(--nospam--at)aol.com Reply-to: seaoc(--nospam--at)seaoc.org To: seaoc(--nospam--at)seaoc.org Can anyone provide comments on the specific advantages/disadvantages of placing a slab on grade vapor barrier directly underneath the concrete slab or below a 3" sand cushion? We are designing a slab on grade system for a office/warehouse facility for which the Geotechnical report does not require the installation of a vapor barrier. However, the flooring system the tenant requires will only install/warranty their product if a vapor barrier is provided. The vapor barrier system they would like to use ("Premoulded Membrane Vapor Seal" from W.R. Meadows or "Moistop" from Fortifiber) recommends placing the vapor barrier directly below the concrete slab while specifying a concrete mix with as low a water-cement ratio as practical, low slump, and wet curing to reduce differential shrinkage and slab edge curling. ACI and PCA recommend a 3" sand cushion to reduce differential shrinkage and curling regardless of the type of vapor barrier used. Please respond ASAP. Thank you. John Carroll, Structural Engineer The McSherry Group, Inc. email: mcsherrygp(--nospam--at)aol.com >> --- Internet Message Header Follows --- Received: from server1.seaoc.org (bqe.com [188.8.131.52]) by host1.texramp.net (8.8.5/8.8.5) with SMTP id XAA02416 for <rlewis(--nospam--at)techteam.org>; Tue, 18 Feb 1997 23:28:17 -0600 (CST) Received: from emout05.mx.aol.com by server1.seaoc.org (NTList 3.02.10) id la004041; Tue, 18 Feb 1997 21:28:06 -0800 Received: (from root@localhost) by emout05.mail.aol.com (8.7.6/8.7.3/AOL-2.0.0) id AAA12460 for seaoc(--nospam--at)seaoc.org; Wed, 19 Feb 1997 00:25:30 -0500 (EST) Date: Wed, 19 Feb 1997 00:25:30 -0500 (EST) From: BCASE1356(--nospam--at)aol.com Message-ID: <970219002530_1147619548(--nospam--at)emout05.mail.aol.com> To: seaoc(--nospam--at)seaoc.org Subject: Re: Location of Vapor Barrier Below Concrete Slab on Grade Reply-To: seaoc(--nospam--at)seaoc.org Error-To: seaoc-ad(--nospam--at)seaoc.org X-Loop: seaoc(--nospam--at)seaoc.org X-Info: [SEAOC] Owner: seaoc-ad(--nospam--at)seaoc.org X-POP3-Rcpt: seaoc-ad(--nospam--at)seaoc.org X-Sender: seaoc-ad(--nospam--at)seaoc.org Precedence: list X-ListMember: rlewis(--nospam--at)techteam.org [seaoc(--nospam--at)seaoc.org] __________________________________________________ Richard Lewis, P.E. Missionary TECH Team rlewis(--nospam--at)techteam.org The service mission like-minded Christian organizations may turn to for technical assistance and know-how.
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