Should you put plastic under concrete slab?

You should NOT place a vapor barrier BEHIND the backer board. Where, pray tell, would any such collected vapor/water go? Answer:There's nowhere proper for such moisture to egress. The current best practice is to place waterproofing OVER the backetboard and just UNDER the tile.

To use this method, ASTM D 4263, “Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method,” a plastic sheet is tightly taped to the concrete. After 72 hours, a humidity reading is taken under the plastic with a dew point hygrometer.

Once the subfloor of proper thickness is properly installed then you can apply cement board directly to the subfloor material. ALL CEMENT BOARDS MUST be installed in a fresh bed of thinset. ... If you want the cement board under the shower tray then do so - doesn't matter.

If the slab is too thin, it may break under load and fail before its time. If the slab is too thick, it costs more than it should. Slab thickness is a major factor in the cost of a concrete floor, so there's often pressure, which can become intense, to make the slab as thin as possible.

Water Cure Concrete made with Portland cement will harden even if it is completely under water.

In fact, one technique for curing a concrete slab is to build a soil dam around the perimeter of the slab, flood the slab with water and keep the slab covered with water for a week..

Yes, you may pour a concrete pad overlay over an existing slab. You need to consider the added height and weight of the overlay on the existing structure. Overlays may include polymers, portland cement concrete, or epoxies. You should improve the drainage of the slab by having a good slope on the overlay.

According to principal investigator Dr John Orr, introducing synthetics like plastic into concrete generally weakens the material, as plastic doesn't bond to the cement mix like sand does.

With dry concrete and the right subfloors and vapor retarders, solid hardwood floors can be installed on slabs that are either on-grade (at ground level) or above-grade (above ground level). ... Wood floors should not be subjected to very wet conditions.

Most exterior slabs do not need a vapor barrier. ... In general, place the concrete slab directly on top of the vapor barrier, with the subbase below. ... The vapor barrier can be placed under the subbase, if the building is closed in when the dry subbase material is placed.More items...

Indoor Concrete Bag Storage Ideally, you should store the bags in a dry and enclosed structure to protect them from rain and moisture. When storing stacked concrete bags for the long term, one idea is to put the smaller bags into an oversized plastic bag and tightly seal it.

Remember that even several inches of concrete cannot stop radon. Some builders believe that the plastic vapor barrier under the slab will stop radon. Although it is a part of the "radon resistant" construction, it merely reduces the flow of soil gas.

No problem plastering straight over cables but if you think you might ever want to pull them out put some plastic capping over them first.

A: It's perfectly acceptable to put tile directly on concrete — with a couple of caveats. First, it is important to determine if there is moisture coming up from the slab. You can test for moisture by taping all four sides of 18-by-18-inch polyurethane plastic on the slab.

During the initial building of a home that has a concrete slab foundation and basement level, any plumbing that runs under the home must be put in before the concrete is poured, since the plumbing runs in the dirt, not within the actual concrete.

You don't need any cement board under the tub. It is far more important to have a sturdy layer of ply under the tub.

Plastic Sheeting Can Permanently Discolor Concrete. Adverse weather conditions such as rain, snow, or freezing temperatures often make it necessary to protect concrete by covering it. ... That's what makes curing concrete with plastic so effective: the plastic keeps the concrete damp.

No plastic sheeting goes behind the cement board. A liquid waterproofing membrane, such as RedGard or Hydro Ban, is applied to the cement board and allowed to cure. Then, tile is installed over the membrane.

Weakened water lines. Since water lines are laid down under the concrete slab, there can be minor damage such as small nicks when the concrete is poured. Although these occurrences may not cause immediate leaks, they can weaken the pipes and grow into a leak-causing crack later.

edit - To put footings under the slab, you can cut holes wherever needed, excavate for footings (Sonotubes or concrete piers or similar) and then patch the concrete slab.

A 50mm thick layer of proprietary floor slab insulation is usually enough to reach and maintain the target U value but this should be checked with an architect first. Insulation sheets should be laid tightly together with the joints staggered to avoid movement.

You don't need any cement board under the tub. It is far more important to have a sturdy layer of ply under the tub.

Embed the cement board in latex-modified thin-set mortar The main reason for using thin-set between the cement board and the subfloor isn't as much for bonding as it is for even, void-free cement board support throughout the floor. ... Then spread thinset mortar with the flat side of a 1/4-in.

Applying a bead of polystyrene-compatible caulk or mastic to the top of the insulation board minimizes water infiltration behind it. For under-slab applications, the rigid foam insulation typically should be installed over a gravel base, with a poly vapor diffusion retarder between the gravel and insulation.

Use wire mesh for driveways that are 4 to 5 inches thick, and rebar for those that are 5 inches or more. Place rebar in a grid pattern with a spacing between bars of approximately 12 inches. In either case, blocks should be used under the reinforcement to keep centered within the concrete.

1.It avoids the possibility of active aggressive agents from soil water being attached to the concrete slab. 2.It prevents the loss of water from cement paste which affects the strength of concrete slab.

Yes, that's true if you use crappy concrete with too much water in it. The easy answer is don't use crappy concrete. ... Here's an idea—get rid of the sand and put the concrete right on the plastic sheet so that the bottom of the concrete mix does not dry out.

Dobies/Chairs: Small concrete blocks or plastic chairs are placed between the base & the wire mesh to hold the wire mesh in the center of the slab. Both come in an assortment of sizes and ensure the wire mesh remains in the center of the slab.

six (6) inchesIt is essential that you keep your concrete slab at no more than six (6) inches of thickness. Also, it would be best to work the numbers out if you wish to work with any lesser as you can only put in one slab.

You should not pour concrete over the grass directly. For your concrete to harden flat and smooth, it is best to clear all vegetation and pour the concrete on top of smooth and debris-free soil. Leaving grass under your concrete slab can cause some unnecessary issues for you in the future.

Water Cure Concrete made with Portland cement will harden even if it is completely under water. In fact, one technique for curing a concrete slab is to build a soil dam around the perimeter of the slab, flood the slab with water and keep the slab covered with water for a week.

Do I need a DPM under laminate flooring? Simply put yes. In order to prevent damp rising through the concrete floor and causing issues, a DPM should be used under all final floor types including wood flooring, laminate, vinyl and floor tiles.

The main purpose of under-floor waterproofing membrane is to prevent rising damp from entering concrete or other floor surfaces. In addition it prevents contamination of concrete during the pouring process.

InstructionsDig Under the Concrete. Dig out the soil, gravel, or other material from under the concrete, using a shovel and a pickax. ... Strike the Concrete. Lightly sprinkle the concrete with water to minimize dust. ... Pry Off Stubborn Pieces. ... Move the Concrete Chunks With a Hand Truck.Feb 19, 2020

edit - To put footings under the slab, you can cut holes wherever needed, excavate for footings (Sonotubes or concrete piers or similar) and then patch the concrete slab.

Another method to prevent discoloration is to place dry straw directly onto the concrete, then put the plastic on top of it. Wet the concrete, then place the plastic sheeting over it. ... Once a day, remove the plastic sheet and wet the concrete, then replace the cover. Do this for a week for the best results.

If you drive over a concrete slab that's got soft ground under it, the concrete wants to bend and stretch. ... If the concrete does develop a hairline crack, the crack should not open with the steel in place. Compacting the soil under the slab before the pour also prevents tension cracking.

Unfortunately, if you have clay-heavy soil, then you may run into difficulty when pouring a slab. The clay can compress under the weight of the concrete, causing the slab to shift or sink over time. ... With proper preparation, however, it's possible to pour a slab on clay soil without encountering these problems.

Place the bag in an airtight tub or buy premix concrete in a bucket. If you need to store a bag of premix concrete, you should put it in an airtight plastic container. Even if the bag is not open, the relatively porous material of the bag can let in air and moisture, allowing the mix to age.

The application of vapor barrier in exterior concrete is unnecessary due to the fact that water penetration does not matter. Any slab on grade that is enclosed and on the interior of a building should have a vapor barrier installed prior to pouring concrete, especially if flooring will be applied.

In California they place sand between slabs and plastic vapor barriers—in Florida they don't. Almost everywhere (except “California”) that slabs are placed on the ground—a plastic sheet—a vapor barrier—is located directly under the concrete slab and on top of the ground (Photograph 1).

InstructionsCover the concrete slab with 4 mil plastic sheeting if you're working near windows.Dig under the concrete if you're able to do so.Start to break the concrete, starting six inches from the edge and working your way in. ... Pry with a long bar or wrecking bar as you go. ... Cut any mesh wire with bolt cutters.More items...•Oct 14, 2019

Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting.

Gravel is especially important in clay soil because it doesn't drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains..

If rain is in the forecast, you should postpone a large concrete pour until conditions improve. Even if rain isn't predicted, you should always be prepared to cover the concrete with a tarp or plastic sheeting just in case. Make sure to seal the edges so rainwater can't seep underneath.

Creating an insulation layer and a vapor barrier between the concrete slab and the ground beneath it is the best practice in insulating basement floors. The insulation barrier will help keep warm air in, and the vapor barrier will keep unwanted moisture out.

Wire mesh makes concrete more durable and increases its strength. The area in which the concrete will be laid down should be covered in mesh before pouring commences.

Even expansion joints in your concrete driveway should be caulked. They can be the biggest culprit of water under your slabs. Notice how the caulking is slightly lower than the concrete slab around it. This protects the caulk from wear and tear of people walking and driving over it.

Plastic Sheeting Can Permanently Discolor Concrete.

Adverse weather conditions such as rain, snow, or freezing temperatures often make it necessary to protect concrete by covering it.

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If the concrete is completely covered with plastic, no outside moisture can penetrate to contact the slab..

Covering the curing concrete with plastic keeps it cleaner, but there is a more important purpose behind this practice. ... To prevent cracks, plastic is placed over the curing concrete to trap the water inside and regulate its temperature, ensuring gradual curing.

The sand layer cannot dry downwards by vapor diffusion because of the plastic sheet—it is a vapor barrier after all. In fact that's why we have it under the slab. We want a vapor barrier under the slab. ** We want to prevent water vapor from coming up from the ground into the concrete slab.

4 inchesWe generally try to maintain a minimum thickness of any slab at 4 inches, if the patio will have heavy features added on it, you may want to thicken it to 6 or even 8 inches, at least under the area where the feature will be added..