Cleanfax, April 2019

Technical Tips Floor covering coating Adhesive Vapor retarder Subbase capillary break Subgrade soil Foundation and soil Usually I start literally from the ground up The term soil can be defi ned many ways A geologist defi nes soil as an altered rock A soil engineer will say its the material that supports or loads a structure at its base Others might defi ne it as a combination of boulders gravel sand silt clay and organic matter Soil provides support for the structure shapes and forms the fi nal grade and in some instances provides disposal for household sewage According to the PCA Soil Primer a booklet published by the Portland Cement Association The moisture or water content of a soil is normally a percentage of the oven dry weight of the soil as tested by ASM D2216 or AASHTO T265 Soil moisture is of three different types Gravitational water capillary water and hygroscopic water Soil type size compaction moisture content chemistry drainage or even testing can play a role as one of the culprits in fl oor failure For instance if a soil is not compacted well or varies in soil chemistries throughout the site concrete fl oor fl atness FF or fl oor levelness FL will be affected causing undulations which can affect some or all of the components of the entire fl oor system Soil and transmission of moisture in soil can seriously affect concrete and fl ooring by eliminating or degenerating the vapor retarder and using a vapor retarder with a lower permanence rate According to Howard M Kanare in the book Concrete Floors and Moisture Vapor retarders must have a permanence rating less than 03 perms according to ASTM E1745 There is no standard specifi cation for vapor barrier compared to vapor retarder However ACI 3021R states True vapor barriers and products have a permanence water vapor transmission rating of 000 perms when tested in accordance with ASTM E96 It is generally accepted in the construction industry that a material having a permanence rating less than 001 perms is considered a vapor barrier In our investigations relating to concrete slab on ground grade even if a vapor retarder is present it sometimes doesnt meet the criteria of what is stated previously in the ASTM E1745 regarding vapor retarders In many instances mil thickness is mistaken for permanence I also have been on investigations in which if a vapor retarder is used with no barrier because of expense it sometimes does not conform to the adaptation of installation requirements made to ACI 3021R Image 2 is a fl ow chart adapted from ACI 3021R 04 in Concrete Floors and Moisture The chart description says It permits omitting vapor retarder for fl oors without fl oor coverings where humidity will not be controlled such as unconditioned warehouse space However it further states that adaptive reuse and installation of fl ooring in such spaces often leads to fl ooring problems due to subslab moisture Therefore vapor retarders should be considered for use under all fl oor slabs I have seen many fl oor failures in which the assumption was a vapor retarder was directly underneath the slab only to face thousands of dollars in fl oor failure expenses because one was nonexistent degenerated improperly specifi ed only located in a portion of the retrofi tted warehouse or specifi ed to go under the dry granular material Surprisingly some specifi ers continue to support the use of vapor retarders under the dry granular fi ll instead of directly under the slab This was changed in ACI 3021R in 2004 after the concrete industry recognized that if the vapor retarder is placed under this dry granular fi ll but gets wet in construction it can unintentionally provide a moisture reservoir through a bathtub affect Now lets examine the other components of the system that can be affected by vapor transmission from the soil or emission from the concrete slab Concrete fl oor slab Recently a fl ooring contractor called with a fl oor emergency 26 CLEANFAX APR 2019 Primer Floor slab Blinding course Filter fabric Leveling compound Image 1 Schematic representation of the components in a slab on ground fl oor system Image courtesy of Portland Cement Association and National Ready Mix Concrete Association