What is the best sub base for a concrete slab? (2024)

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What is the best sub base for a concrete slab?

Most concrete contractors want a mix of coarse and fine aggregate to create a compactable base that is going to be safe for settlement and drainage. Crusher run (a mix of crushed stone and stone dust) and #57 coarse aggregate are two of the best base materials for concrete slabs.

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What is the best material to put under concrete slab?

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, they may rot and cause unevenness.

What is the proper sub base for concrete?

Subbase for Concrete Slab

Subbase is a layer of gravel, which is fairly cheap material, placed on top of subgrade. The subbase placement is optional and it serves as a work platform for construction of the slab and provide more uniform support for the slab.

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Is it better to put gravel or sand under concrete slab?

As a general rule, stay away from using sand as a subbase. You're better off using gravel. Your concrete will last longer and have less of a chance of cracking over time.

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How thick should a concrete slab sub base be?

As a rule of thumb, concrete slabs supporting lighter weights such as paths, patios and shed bases will need to be 75-100mm thick, while driveways and garages need to be at least 100mm thick.

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Should you put plastic sheet under concrete slab?

All concrete slabs used in heated structures must have a vapor barrier installed. A minimum of at least 6-mil polyethylene vapor retarder must be installed between the concrete and prepped ground, according to the 2018 IRC.

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How much sand is required under a concrete slab?

Uses for packing sand:

Mainly used under concrete slabs: Create a barrier between the concrete and the soil by pouring a 50mm - 100mm layer of sand or gravel into the bottom of the frame, this will prevent the clay soil from absorbing moisture from your concrete.

(Video) Sub base preparations for a driveway
How much sand do I need under concrete slab?

For gravel, you'll need 4–6” of ¾ minus crushed gravel. One yard of gravel covers approximately 80 square feet. For the sand, you'll need 1” of concrete sand. One yard of sand covers about 200 square feet.

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Can I pour concrete over dirt?

Long story short, yes you can pour concrete over dirt. However, you need to follow the process outlined in this article for the best results. If this all seems a bit overwhelming, we suggest reaching out to a professional concrete contractor.

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What kind of Styrofoam do you use under a concrete slab?

The most common types of under slab or concrete insulation include rigid foam insulations, such as expanded polystyrene (EPS), extruded polystyrene (XPS) and radiant insulation, such as Prodex.

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What is the best Styrofoam for under concrete?

Expanded Polystyrene

EPS comes in various sizes and compressive strengths and has a meager water absorption rate, which makes it an excellent option for under slab insulation. Expanded Polystyrene has an R-value of about 3.6 per inch and can maintain its R-value over an extended period.

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What is the best gravel base for concrete?

Medium gravel, which is 1.8 cm (3/4 inch) in diameter, is the best material for a concrete base.

What is the best sub base for a concrete slab? (2024)
What is a typical sub base material?

The subbase is the layer of aggregate material that lies immediately below the pavement and usually consists of crushed aggregate or gravel or recycled materials (see Section 6C-1 - Pavement Systems for more information).

What is the best concrete base mix?

The safest bet for any concrete mix is four-two-one: four parts crushed rock; two parts sand; and one part cement. The four-two-one mix, obviously, has seven parts. Conveniently, when mixing concrete, the ratio can be mixed on any range of scales.

Why put sand under concrete slab?

To prevent cracking and crumbling, concrete patios need to be built on solid, well-drained soil. If you live in a region with lots of clay in the soil, you will need to dig down further and backfill with layers of compacted sand and gravel.

Can I use river rock for concrete base?

1 Answer. Yes, it can be used in foundations and subbases of roadways if the rocks meet property and gradation requirements. However, crushed stone/gravel is often the choice for the base material.

What is the gravel under a slab called?

Subgrade—this is the native soil (or improved soil), usually compacted. Subbase—this is a layer of gravel on top of the subgrade. Base (or base course)—this is the layer of material on top of the subbase and directly under the slab.

Should you put foam under concrete slab?

For Climate zones 1 to 3, installing rigid foam insulation under a concrete slab is optional, but it's best to have one to improve energy efficiency. If you're installing heated slabs in zones 1 to 3, the rigid foam insulation to a depth of the footing or 2 feet.

Do I need a vapor barrier under my slab?

Without a vapor barrier in place, a slab that dries from its top surface will be exposed to disproportionate moisture levels in the slab for its entire lifetime. This can be a far greater curling threat to the foundation, long-term.

Does my slab need a vapor barrier?

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.

What is the cheapest way to pour a concrete slab?

Working With Ready-Mix Concrete

And, if you mix it yourself, it's the cheapest way to make your slab. For most do-it-yourselfers, the best material for building a concrete slab is a ready-mix, crack-resistant concrete product. The wet mix is poured into a prepared wood form, then left to cure.

Where does rebar go in concrete?

Reinforcement should also be placed low enough so saw cutting does not cut the reinforcement. For welded wire reinforcement, the Wire Reinforcement Institute recommends steel placement 2 inches below the surface or within the upper third of the slab thickness, whichever is closer to the surface.

How deep do you dig for a concrete slab?

In most areas, a concrete patio begins with 4 inches of compacted stone. The difference is the depth you dig before you pour. If you install a concrete patio, dig out a space 8 inches deep; 4 inches for the some, another 4 inches for the concrete, and another 2 inches to allow for mortar and brick.

What kind of sand do you use on a concrete slab?

Sharp Sand (which has larger grains) is used for concreting or laying paving slabs and Soft Sand is used for bricklaying, etc. It is also possible to buy mixed aggregate containing both coarse and fine aggregates.

What size sand is best for concrete?

Sand for concrete work

Depending on the percentage of the various sizes of sand present in a sample, sand for making concrete is grouped into five zones - Very coarse, Coarse, Fine, Very fine and Very very fine. Most of the particles present in the sand may be of 4.75 mm or 5 mm.

How much cement sand and gravel do I need for concrete?

In terms of the ratio for concrete, it depends on what strength you are trying to achieve, but as a general guide a standard concrete mix would be 1 part cement to 2 parts sand to 4 parts aggregates. For foundations, a mix of 1 part cement to 3 parts sand to 6 parts aggregates can be used.

Why remove grass before pouring concrete?

Technically you can, but you really shouldn't pour concrete over grass. To maintain its tensile strength, concrete needs to be laid on a firm, even, and dry foundation. Grass and soil will naturally channel moisture into the concrete from below, which will likely result in it cracking over time.

Should I wet dirt before pouring concrete?

When pouring concrete directly on the soil, the soil must be damp to ensure proper curing. However, when the soil is saturated with water, it is too wet and could adversely affect the concrete curing process. Concrete hardens through a process called curing.

How do you compact soil for a concrete slab?

To compact soil ready for a concrete slab, a mechanical compactor should be used. A plate compactor is the most common tool used to compact soil for a concrete slab. For small areas, a hand tamp may do the trick, but a mechanical compactor is better. Strong metal plates and lots of force compact soil best.

What PSI should foam be under a slab?

under slab insulation is a high performance, high compression strength (35 psi) flat-sheet insulation material made from expanded polystyrene (EPS) which is bonded to a reflective film laminated on both sides.

Should insulation go over or under slab?

Insulation below the slab is more common and arguably better as the slabs help to absorb the heat, meaning overheating is less likely. The DPM is placed over a layer of sand to protect it from the sharp concrete stones (otherwise you risk puncturing the insulation).

Does Styrofoam need a vapor barrier?

The short answer is - it depends. In general, if the foam rigid insulation is installed correctly and sealed properly, a vapour barrier may not be necessary.

Can I use expanding foam under concrete?

Polyurethane foam can level your concrete slabs by providing a supportive, strong layer below your slab.

Does more gravel make concrete stronger?

Larger pieces of gravel create a “course” concrete that is extremely strong but somewhat unwieldy. Gravel adds a lot of strength to concrete but, if you use too much, it has the opposite effect and damages the integrity of the concrete mix.

Can gravel be used as sub-base?

There are a variety of different materials that can be used for the sub base, but crushed stone, gravel, or sand are commonly used. Crushed stone or hardcore is usually the best option because it's easy to work with but is more durable than sand.

Should vapor barrier go above or below gravel?

You need to put the gravel down first and then put the vapor barrier on top to keep your crawl space dry and free from crawl space mold. When a vapor barrier is incorrectly installed underneath the gravel, any water that does get in can't get out.

What surface will concrete not stick to?

Paint – Paint is another material that has no natural bonding agents, so concrete generally won't stick to it very well. Oil – Oil or oiled surfaces are often used to make the surface resistant to concrete bonding.

Why do you put black plastic under a concrete slab?

Plastic should be placed under a concrete slab to protect it from moisture damage. Moisture from soil can penetrate the concrete causing it to crack with time and potentially risking lots of structural damage. A vapour barrier put under a concrete slab such as plastic sheets can protect it from this.

What material is used beneath a slab to prevent moisture through floor slab?

The most commonly used vapor barrier under concrete slabs is polyethylene (poly) plastic sheeting with a thickness of 10 mil or 15 mil. All Americover Vapor Barriers are composed of virgin polyolefin resins and offered in 10 mil, 15 mil, and 20 mil.

How do you waterproof under a concrete slab?

Under-slab waterproofing has some very unique challenges. There are really just two options: either put a sheet/rolled waterproofing membrane under the the slab, or use chemical admixtures such as Xypex and Concur to waterproof the concrete and block vapor transmission.

What stops concrete from setting?

If the ambient temperature is too low, the hydration of the cement will drastically slow down or completely stop. Cold weather slows down the setting process or stops it completely, negatively impacting the concrete's strength gain.

How long to leave concrete in plastic molds?

Place the mold on a vibration table and fill with concrete. Allow the concrete to cure for 24 hours and then demold casting. You've created a perfect concrete reproduction of the original! The rubber mold is ready to be cast again.

Does concrete need to breathe?

Covering your concrete basem*nt floor with a different material can be detrimental to its longevity and condition. This is because the concrete needs exposure to air in order for it to breathe properly.

What are the disadvantages of using plastic in concrete?

Using synthetics like plastic in concrete generally weakens the material because they do not bond to the cement mix as well as sand. Properties such as the type of plastic, particle size and shape, and the rheology of the wet mix all have an influence on the strength of the finished concrete.

What is the best moisture barrier underlayment for concrete?

ECF is the ONLY underlayment with a built-in 6 mil moisture/vapor barrier. This Class 1 vapor barrier offers the highest level of moisture protection available. In particular, ECF is the ideal underlayment for use on concrete subfloors, including basem*nt applications.

What is the best moisture barrier for concrete slabs?

The American Concrete Institute (ACI) also recommends a minimum of 10 mil polyethylene or thicker for vapor retarders under concrete. According to its Guide to Concrete Floor and Slab Construction ACI 302.1R-15, thicker poly provides a better barrier and is also more puncture resistant.

What is the best moisture barrier?

Class I -This is the highest barrier class because it is impermeable. It's also the strongest vapor barrier class. It includes glass, sheet metal, polyethylene sheets, and rubber.

What is the best waterproofing for slab?

Polyurethane Waterproofing Treatment

This coating has exceptional crack-bridging properties, flexibility and durability, excellent bonding with concrete and construction materials. It also renders the substrate breathable, water-resistant, and weatherproof.

What is the best waterproofing for concrete?

Polyurethane is considered one of the best waterproofing materials. It can be applied seamlessly and penetrates the surface deeply and evenly. Thus, the polyurethane membrane will fill in even the finest cracks in concrete, reducing its water absorbency capacity.

What is the best thing to waterproof concrete with?

One of the best concrete sealers is the Siloxa-Tek 8500. It is a penetrating concrete sealer designed to treat a variety of applications with an emphasis on hydrophobicity and reduction of water uptake. It dries completely clear with a natural finish that will not change the look or appearance of the susbtrate.

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