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  • gravel under concrete slab is it absolutely required

    gravel under concrete slab is it absolutely required

    May 01, 2017 It depends what you need gravel can provide a capillary break preventing water from wicking upwards, can facilitate drainage, and can facilitate gas movement like radon. So in some cases, these are not always important factors. According to BSI-003 Concrete Floor Problems, Joseph Lstiburek, May 26, 2008

  • Crushed Stone Under Concrete Why Its Needed

    Crushed Stone Under Concrete Why Its Needed

    Concrete is porous, and will therefore absorb water after a heavy rain. This water can pool underneath your slab unless some form of drainage is provided. Should this happen, your slab can actually erode a bit over time. Adding crushed stone under concrete is an excellent way to allow water to drain, because it can flow through the spaces between rocks, thereby preventing it from standing underneath the surface. It also provides a barrier between the soil and the slab

  • 3 Reasons Why Its Important To Use Crushed Stone Under

    3 Reasons Why Its Important To Use Crushed Stone Under

    Apr 28, 2014 Adding crushed stone under your concrete slab will provide a level surface for your foundation. Simply pouring concrete onto the ground will expose it to elemental erosion that will cause cracking and sinking. Similarly, if there are roots or plants under your slab,

  • How much gravel is needed for a concrete slab

    How much gravel is needed for a concrete slab

    Mar 26, 2020 What type of gravel goes under concrete Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.

  • Gravel under Concrete Slab Pilots of America

    Gravel under Concrete Slab Pilots of America

    Jun 28, 2016 I was told the gravel is for sub-level drainage.....wet concrete in the winter freezes then cracks. We also put plastic down as an extra barrier then the wire. Oh, the steel or wire used is what gives the concrete tensile strength....not so much extra thickness. CheckoutmySix, Jun 23, 2016

  • why sand under concrete Fine Homebuilding

    why sand under concrete Fine Homebuilding

    Aug 19, 2004 Im preparing to pour a finish concrete foor, slab on grade. The structural plans call for 4 compacted gravel base, insul-tarp vapor barrier, 2 of sand and 4 of concrete. What purpose other than a base for the concrete does the sand serve Why use it when yopu have thick insul-tarp

  • Subgrades and Subbases for Slabs Concrete Construction

    Subgrades and Subbases for Slabs Concrete Construction

    Nov 22, 2017 Almost 20 years ago, Concrete Construction investigated the effect of using a layer of loose uncompacted sand directly beneath a concrete slab and concluded that this practice contributed to more later-age cracks and poorer joint performance. Here are the reasons not to use a sand layer Difficult to maintain a flat, level sand surface during concrete placement Difficult to ...

  • Does Anybody Use Sand as a Base Before They Pour

    Does Anybody Use Sand as a Base Before They Pour

    One reason it is used as a backfill or sub-grade material. As with all material, it has to be placed correctly and compacted properly. Sand needs to remain damp as well as other material before placement of the concrete. If you want to build a road, use gravel, but this does not mean you will not have issues.

  • Gravel under Concrete Slab Pilots of America

    Gravel under Concrete Slab Pilots of America

    Jun 28, 2016 For the Civil Engineers out there. Does anyone know of any real reason to spend the money to put gravel under a concrete slab I have always just graded the dirt under the slab so it drains off to the sides or bottom same as the concrete slab will drain, compacted it and called it good.

  • What is the best base for concrete slab

    What is the best base for concrete slab

    Apr 17, 2021 Slab Foundations Like all foundations, the slab starts with concrete footers poured 24 inches below projected finish grade. What should you put under a concrete slab Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete

  • Quick Answer Do You Need Gravel Under Concrete

    Quick Answer Do You Need Gravel Under Concrete

    Excavate the slab area to a depth of about 7 inches, allowing 3 inches for a gravel base and 4 inches for concrete. What kind of gravel do you put under concrete Backfill beneath concrete flat-work along foundation walls should be accomplished with a granular material that is uniform in size.

  • Can I use pea gravel under concrete

    Can I use pea gravel under concrete

    Mar 02, 2020 Pour concrete over a solid, well-drained base Because concrete slabs float on the soil, soft ground or voids underneath may cause unsupported areas to crack under heavy weight like vehicles. Pack about 4 in. of sand or gravel over clay and other poorly draining soils to provide even support.

  • Crush and Run Instead of Gravel Under Slab

    Crush and Run Instead of Gravel Under Slab

    Sep 17, 2020 Malcolm, I had assumed 4 was sufficient. If it needs 6 , I will comply, but at 675 per 22ton load, it hurts. Also, when you say - top dress the 6 below the slab with a drainable fill - you are talking about the 34 gravel between the ground and the concrete, or in my case between the ground and Fomular 250 25 psi foam and then concrete.

  • Polyethylene Under Concrete Slabs GreenBuildingAdvisor

    Polyethylene Under Concrete Slabs GreenBuildingAdvisor

    Jul 04, 2014 What goes under the concrete in a slab-on-grade home In the old days, not much just dirt. Eventually, contractors discovered that it made sense to include a 4-inch-thick layer of crushed stone under the concrete. The crushed stone provides a capillary break that reduces the amount of moisture flowing upward from the damp soil to the permeable concrete. Since the crushed stone layer ...

  • compact fill under slab Ask the Builder

    compact fill under slab Ask the Builder

    DEAR TOM Un-compacted fill under concrete slabs of any type is a recipe for disaster. The slab could be for an entire home, it might be an exterior patio slab, a front porch slab, a driveway, etc. Concrete is an amazing material, but it has an Achilles heel.

  • Should You Put Rigid Insulation Under Concrete Slab

    Should You Put Rigid Insulation Under Concrete Slab

    Depending on where you live, rigid insulation under a concrete slab might be required The IECC, a regulatory code that ensures new construction is environmentally conscious, requires a minimum of R-10 insulation in Climate Zones 4-8. You can check if you live in one of these zones on the IECC zone map.. If the IECC requires rigid insulation under concrete slab, youll also need to get an ...

  • Dont Use Loose Sand Under Concrete Slabs Concrete

    Dont Use Loose Sand Under Concrete Slabs Concrete

    Mar 01, 1999 Dont Use Loose Sand Under Concrete Slabs. Will using a thin sand layer under floor slabs reduce subgrade or subbase support, causing cracking and poor joint performance, especially under repeated loadings such as forklift traffic To gather data to help answer this question, The Aberdeen Group performed California Bearing Ratio tests on three ...

  • Concrete Slab How to install a slab from start to finish

    Concrete Slab How to install a slab from start to finish

    How to build a Concrete Slab. A concrete slab is poured right on the ground. It doesnt have a foundation or any concrete walls under it or around it. In Maine we install a lot of slabs-on-grade for houses and garages. A slab foundation is usually less expensive to install than a full concrete wall foundation with a concrete floor.

  • Concrete Vapor Barriers for Under Slabs The Concrete

    Concrete Vapor Barriers for Under Slabs The Concrete

    The last thing you want your customers to envision when thinking of a concrete floor is a damp, cold basement slab. One of the reasons those old basement floors were like that was because they had no vapor barrier beneath them, leaving an easy path for water vapor from the soil to migrate into the slab, assuring that the cold clammy damp feeling never went away.

  • Importance of Gravel and Sand for Concrete Hunker

    Importance of Gravel and Sand for Concrete Hunker

    Smaller gravel particles equals a fine grade of concrete. Use the fine aggregate for concrete slabs or other smooth surfaces. A coarse aggregate means using larger pieces of gravel. Coarse concrete is helpful for sturdier projects. Concrete with a coarse aggregate doesnt produce a smooth look or feel but is stronger than a finer grade.

  • What size gravel is best for concrete

    What size gravel is best for concrete

    Coarse gravel, like 57 stone, under a slab is used as a capillary break to prevent ground moisture wicking up through the concrete. All good concrete needs the bottom almost as flat as the top, creating a uniform thickness to maximize strength.

  • Proper Subgrade Prep Concrete Construction Magazine

    Proper Subgrade Prep Concrete Construction Magazine

    Sep 20, 2007 With slab-on-grade foundations, an alternative to native soil material may be used to restore grade. These imported fills may include granular materials such as sand, gravel, or crushed stone. These high-strength and permeable materials offer low compressibility, which is ideal for a slab

  • Quick Answer Do You Need Gravel Under Concrete

    Quick Answer Do You Need Gravel Under Concrete

    Why do you put gravel under concrete Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.

  • What size gravel is best for concrete

    What size gravel is best for concrete

    Why do you put gravel under concrete Coarse gravel , like 57 stone, under a slab is used as a capillary break to prevent ground moisture wicking up through the concrete . All good concrete needs the bottom almost as flat as the top, creating a uniform thickness to maximize strength.

  • Can I use pea gravel under concrete

    Can I use pea gravel under concrete

    Mar 02, 2020 Gravel is especially important in clay soil because it doesnt drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains. Gravel allows water to drain into the ground below. When packed tightly, however, the

  • Concrete Vapor Barriers for Under Slabs The Concrete

    Concrete Vapor Barriers for Under Slabs The Concrete

    All of the problems associated with moisture vapor movement in a concrete slab will go away in time as the slab dries, as long as there is no source of additional water into the slab. Since the most common source is moisture in the ground beneath the slab, the solution is to completely take the ground out of the equation, by sealing the bottom of the slab.

  • How to Prepare the Ground Before Pouring Concrete Slab

    How to Prepare the Ground Before Pouring Concrete Slab

    Determine the proper depth by establishing the height of the concrete slab. Add 2 inches to the depth for gravel if the soil is normally moist or has a high concentration of clay. Most concrete slabs will sit 1 to 2 inches higher than the dirt and 2 to 3 inches below the surface of the dirt, making the needed depth of the hole 3 to 5 inches.

  • Gravel Or Sand DIY Home Improvement Forum

    Gravel Or Sand DIY Home Improvement Forum

    Jul 11, 2010 Wouldnt the v.b. under a patio slab keep the water from draining, if the slab was poured on the leveled sub-grade for a patio And possibly freeze easier if the slab is covered with snow that melts into the porous concrete slab during the day- pooling there to freeze at night

  • Concrete Slab Surface Defects Causes Prevention Repair

    Concrete Slab Surface Defects Causes Prevention Repair

    The appearance of blisters Fig. 1 on the surface of a concrete slab during finishing operations is annoying. These bumps, of varying size, appear at a time when bubbles of entrapped air or water rising through the plastic concrete get trapped under an already sealed, airtight surface. Experienced concrete finishers

  • The Dirt on BelowGrade Insulation Insulfoam

    The Dirt on BelowGrade Insulation Insulfoam

    Aug 14, 2014 Up to one-quarter of a buildings energy loss is due to lack of insulation in below-grade areas, including the foundation and under slabs. Now that high-performance building envelopes are common above ground, the relative amount of total heat lost below grade

  • How to Pour a Slab on Clay Soil Home Guides SF Gate

    How to Pour a Slab on Clay Soil Home Guides SF Gate

    Dec 14, 2018 The more compressed your soil is, the less likely it is to cause significant damage to your concrete slab as a result of continued compression, and the more overall weight it can support.

  • How to build a SlabonGrade Ecohome

    How to build a SlabonGrade Ecohome

    Jan 06, 2014 Whether you start construction with a slab-on-grade or a foundation, in the absence of bedrock both will be resting on dirt. So one is not more stable than the other, or more suceptible to frost heave than the other, if it is properly insulated around the perimeter.

  • Do You Need Gravel Under Concrete Patio Slab Footings

    Do You Need Gravel Under Concrete Patio Slab Footings

    Why Do You Need Gravel Under a Concrete Gravel, or crushed stone, provides a stable surface for your concrete slab. Even the most solid, compacted soil can shift dramatically with the weather changes, which will undermine your slab and cause cracks. It is important to note that not all gravel is the same.

  • Slabs for Colder Climates Part 1 The How and Why of

    Slabs for Colder Climates Part 1 The How and Why of

    Apr 10, 2012 Lets start with the money savings, however. A slab may still be the most affordable foundation, but if you use conventional techniques, the difference in cost between full basements and slabs will be marginal you dig below the frost line, 36 or more, and then pour a foundation before forming the slab.

  • Insulating a SlabOnGrade Foundation Fine Homebuilding

    Insulating a SlabOnGrade Foundation Fine Homebuilding

    Jul 09, 2014 In cold climates, most slab-on-grade foundations include perimeter stemwalls or frost walls that extend 3 ft. or 4 ft. below grade. The area between the stemwalls is usually filled with compacted gravel to support the slab. Because they are easier to insulate, slab foundations with stemwalls are preferable to monolithic slabs.

  • The Recommended Gravel Base for a Concrete Driveway

    The Recommended Gravel Base for a Concrete Driveway

    Apr 27, 2021 Concrete Network explains that the two levels underneath driveways include the subgrade of native soil topped with a subbase of gravel underneath the concrete slab

  • How to Pack Down Rock Before Pouring Concrete Home

    How to Pack Down Rock Before Pouring Concrete Home

    Dec 09, 2018 Gravel is especially important in clay soil because it doesnt drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains. Gravel allows ...

  • The Dirt on BelowGrade Insulation Insulfoam

    The Dirt on BelowGrade Insulation Insulfoam

    Aug 14, 2014 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. Additional insulation is applied along the edges of the slab, because that is a primary surface for heat loss.

  • How to build a SlabonGrade Ecohome

    How to build a SlabonGrade Ecohome

    Jan 06, 2014 The more traditional method for building a slab on grade is to first pour a footing, wait a few days, then pay those very expensive concrete trucks to come back a second time to pour the slab of your house. and its even worse with a basement because it takes 3 trips once to pour the footing, once for the walls, then later for the slab floor.