I’m concerned that a vapor barrier would trap moisture underneath it. Would pouring a new slab over the existing one be something to consider? I am scheduled for concrete pouring already in the next 2 days but this situation concerns me. ASTM International gives specific guidelines in ASTM E1745-17 and ASTM E1643 for the use, installation, and inspection of vapor barriers used under concrete slabs. Do not add too much water, you do not want your mix too sloppy. Great questions. Digging the trench is the hardest part of this task. Thanks for the comment. Obviously, there could be other culprits, but these are the two that come to my head immediately. stream Thanks for the question. Should I be concerned about humidity build up between the vapour barrier and the concrete? (or possibly the contractor didn’t prep the floor properly or mix the thinset properly) so today i ripped up all the tile and halted the project until i can find answers…i really want to install tile again but my question is if I should use a painted sealer like redgard or something different to prevent moisture vapor to escape and ruin another attempt at tile! And is engineered hardwood any better? Sealer should be applied at least once a year. If you are going to do some type of finish, most would recommend a vapor retarder. After the concrete is poured and smoothed, the finishing crew uses a variety of tools to work … If the basement slab was poured directly on the ground, rather on a true vapor barrier, then the ground underneath the slab will always be ‘in play’, and the moisture in the ground below will always want to move upward to the slab’s surface. You need to make sure that there is no organic matter under where the driveway will be located, remove any sticks, roots, grass, or other plants that are there. Thanks for the comment. on Twitter Share "Do you need gravel under concrete driveway?" Homeowners take great … On the other hand, the sheet also helps to ensure there is a break between the blotter layer and the concrete to keep groundwater from entering the slab later in its life. The front and one side of the shed will not have walls. Thanks for the comment/question. Condensed water pools wherever the plastic touches the slab, but the concrete under the air pockets remains dry. Good luck! The concrete slab is then poured on top of it. I would probably want to verify if there is an intact vapor retarder, prior to planning. If no, then you need to utilize a mitigation product that will warrant up to 100% RH and will do so even if an intact retarder isn’t present. The only real way to know for sure is to have core samples taken of the slab by a geotechnical type of firm. It makes me wonder if that may potentially be a perfect environment for mold growth. Home » The Rapid RH® Concrete Moisture Test » Concrete Information & Knowledge Base » Subfloor Moisture » Concrete Vapor Barriers: Everything You Need to Know. Thanks for the question. They are a network of flooring inspectors. will it help? My dad and husband just poured two footings in our basement and forgot to put down the 6mil poly specified by the engineer before pouring the concrete. During custom home construction, often new homeowners ask why the builder places black plastic under the concrete slab for their home. I was really scared, I thought I was in a movie and dreaming too… I called the fire dept. If Pergo is the finished product, I would start by calling their technical hotline (after quantifying the moisture levels) and asking them for recommendations or guidance. You should be able to find some type of geotechnical service in your area that can perform a core sample test of the garage floor. was not leveled at all. <>/XObject<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 595.56 842.04] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> In the pieces of wood that have been removed, sometimes it appears that moisture was between the adhesive and the slab and in some cases it looks like the moisture was between the adhesive and the wood. You will need to do research though to make sure warranties for these types of products are applicable to basement settings where hydrostatic pressure may be at play. My fear would be more about the floor being ruined than mold. We left the boards out for over a week until the floor was dry. Help me!???? According to the Guide to Concrete Floor and Slab Construction published by the American Concrete Institute, a vapor retarder should not be less than 10 mils thick. I am guessing that you are trying to ensure there are no moisture related issues with the flooring you are going to install? Otherwise, what is under a slab depends on the ground you are pouring the slab on, some soils don't need anything, some need a lot of help. I have a 140 foot driveway and need to know if I can lay gravel over the grass. Call Total Concrete on 0800 859 5371 to get a quote, or use our online booking form. Given that the “interior” will be so open to the elements, is there any benefit to installing a vapor barrier under the concrete slab? If this is a slab on grade vs slab below grade (which you don’t specify) then I am not sure why solid wood would not be appropriate. Nick. Great information. I live in Florida on the west coast. Anyone that has had to face a moisture problem with a concrete slab understands the damage that excess moisture can cause. Could this be caused by moisture in the slab or no vapor barrier? Seven days is best for a driveway. Thanks for the comment. Based on these results, shop the product that handles your moisture testing results. We were looking at a lumber liquidator barrier with pre-applied adhesive and would possibly glue the boards in the area where the runs are greater than 27 feet… It sounds like you may have a traditional mortar bed installation here. on Facebook Post status "Do you need gravel under concrete driveway?" Guide to Concrete Floor and Slab Construction, http://www.elitebuilding.com/tile/ref/trowelsize.htm, https://www.tcnatile.com/faqs/71-thick-setthick-bed.html, https://www.concreteconstruction.net/how-to/new-slab-on-top-of-old_o, https://www.stegoindustries.com/stego-wrap-vapor-barriers?hsCtaTracking=d654940e-2168-473c-934d-ed294b689fe3%7C23dd2231-f515-494b-8e7f-b042972bd744, 3 Key Lessons about Moisture from an Old Concrete Floor. Based on your situation, it may be best to ensure you have proper ventilation and airflow in the air space. for this. Hi Jason, Don’t know which way to go! Under some building codes the lower strength mix requires the use of a vapour barrier where as the higher strength mix does not. These can be made in a variety of sizes, and of a variety of materials. Thanks for the question. During custom home construction, often new homeowners ask why the builder places black plastic under the concrete slab for their home. It will hold a little more water, but nothing thats major. It will have a laminate floor when done. I would always have to defer back to your local building code on this. I am looking to build a camp on a slab. They put down a plastic Barrier which I discovered the other day had a puncture. It will have a concrete slab, a sheet metal roof, and two concrete block walls. That being said, there are some coatings companies that use these devices in their installation documents. After moving in I discovered, on the stick built 4th exterior wall, a spot of mold on the interior drywall covering the stick built section. The same process was performed. The contractor says that we must have a cracked slab that’s letting in moisture and that his installation technique was fine. It seems to be more gravel and sand. Capillary breaks do a good job of stopping water in its liquid state from reaching a slab. I will assume cosmetic based on how you described it. (949) 325-2035. Just using concrete as the floor. Due to expenses of resident turnover, they decided to remove carpet/pad/tack and replace with sheet vinyl everywhere excluding Bedrooms, on the first floor for each of the properties. Keep the concrete damp for a week. One common building reinforcement material is rebar. Another possibility, or it could be some combination of both, you may be dealing with is some type of condensation issue, but I would think there would be signs on the rest of the floor if that were the case. There should be more than a 5 degree temperature variation between actual and calculated temperature to avoid condensation (sweating). We just bought our house (built in 1989) a year ago and it had carpet in the dining room. Hello, The boards were installed again. Thanks!. In cool and moderate conditions, cover it with plastic. As the soil settles or is carried away by other means a gap opens up between the soil and the bottom of the concrete slab resulting in a loss of support. Condensed water pools wherever the plastic touches the slab, but the concrete under the air pockets remains dry. Under hot conditions, above 80 degrees F, frequently water it down with a garden hose to keep it moist. 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