How much gravel do you put under a concrete pad?

Asked By: Carmen Pinsky | Last Updated: 24th January, 2020
Category: business and finance construction industry
4.6/5 (1,082 Views . 13 Votes)
A minimum thickness is 4-6 inches of well compacted gravel should be your target. Any more depth of gravel is ok with the proviso that it be well compacted.

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In this regard, what kind of gravel do you put under concrete?

It should also compact easily and be evenly compacted before the concrete is poured to provide strength and stability. Recycled gravel is suitable for use beneath a concrete driveway as long as it is clean and uniform.

Subsequently, question is, what is the best base for concrete slab? Subgrade and subbase are the foundation of a concrete slab and play critical role in its performance. According to the ACI Code, the subgrade is a compacted and improved natural soil or brought infill whereas subbase is a layer of gravel placed on the top of the subgrade.

In respect to this, is gravel needed under concrete?

Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel allows water to drain into the ground below. When packed tightly, however, the gravel doesn't shift beneath the concrete.

What do you put under a concrete slab?

Just scrape off the sod and topsoil and add gravel fill if needed. If you have clay or loam soil, you should remove enough to allow a 6- to 8-in. layer of compacted gravel under the new concrete. If you have to remove more than a few inches of dirt, consider renting a skid loader or hiring an excavator.

27 Related Question Answers Found

Should you put plastic under concrete?

Vapor retarders have been used since the 1950s. Recently, though, research has shown that the old traditional layer of 6-mil Visqueen (polyethylene plastic) under the slab is seldom effective for two main reasons: Although it may seem water-tight, this grade of material allows a lot of water vapor to pass through.

Can you pour concrete on dirt?

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.

When should I start watering my concrete?

Be sure to start watering the concrete in the morning and keep watering throughout the hottest part of the day. Do not start watering during the hottest part of the day because it could shock the concrete into developing surface crazing (similar to a hot glass breaking when filled with cold water).

Do you need rebar for 4 inch slab?

If you don't put rebars in a 4-inch [10 CM] slab, then it won't be reinforced concrete - and won't perform. As a general rule, any section of concrete must have at least 0.25% of its area in rebars to be considered reinforced concrete and do the intended job.

Can you use pea gravel under concrete?


Pea gravel is a loose landscaping material composed of smooth, rounded stones between 1/8 and 1/4 inch. While pea gravel can be used as a mulch alternative, garden border and other landscaping purposes, it is not the best choice for a patio base.

Do you put gravel under footings?

If the soil is very strong, this may not lead to problems. In soils with bearing capacity greater than about 4,000 psf, I suggest excavating next to the footing and under it, and placing compacted large gravel into the space. That should be adequate to support the wall.

Will crushed concrete harden?

Crushed Concrete: A fantastic driveway stone, hardens and compacts over time. Easy to install and long lasting. The product is run through magnets to remove most of the non-cement pieces from the recycling process. A few pieces of metal can sometimes be found.

How much gravel do I need under my shed?

As a rule of thumb, your gravel shed base should extend at least 12” further than each side of your shed. For example, if you are building your shed foundation for a 10×12 structure, you should make it at least 12×14.

How do you prepare the ground before pouring concrete?


Preparation is the most important aspect of pouring a concrete slab.
  1. Dig the ground down to the proper depth.
  2. Smooth out the ground with the flat side of a rake so that you have a level surface.
  3. Tamp the ground with a hand tamper or mechanical tamper.
  4. Pour 2 inches of small, rounded gravel for additional drainage needs.

What size crushed stone for concrete slab?

Question: What size aggregate should be used to make the concrete for a 4 inch slab? Top Answer (37% of 40 votes): 3/4 inch crushed stone. Explanation: #57 rock (3/4) is best for strength. COMMON SENSE FLOORING, INC.

How thick should a concrete patio be?

We 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.

Can I pour concrete over old concrete?

If the existing concrete is in good shape structurally, you can pour new concrete over it to freshen it up. Proper prep work is key to success when layering new concrete over old. If the existing concrete is in good shape structurally, you can pour new concrete over it to freshen it up.

How do you prepare subgrade for concrete?

DIY Concrete: How to Prepare Your Subgrade
  1. Clear the area. Before you start any concrete project, you need to be sure you have a clear area.
  2. Backfill. Unless you are pouring on virgin clay, the area will need to be backfilled with either sand, gravel or crushed stone.
  3. Compact the subgrade. Compacting the subgrade is very important.
  4. Forming.

What size gravel do I need for my driveway?


In general, driveway gravel should be relatively large, between about 3/8 and 3/4 inch in diameter, as compared to the gravel used for footpaths, which is typically 1/4 to 3/8 inch in diameter. Another factor to consider is the amount of very small granular material, called "fines," in the gravel.

Do I need a vapor barrier under my concrete slab?

Water vapor will always move from a high relative humidity environment below the building into an area of low relative humidity – even through concrete. That's why nearly every expert in the concrete industry recommends a below-slab vapor barrier to stop the vapor drive of water upward and into your building envelope.

Why do you put plastic under a concrete slab?

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.