How Much Gravel Do You Put Under a Concrete Slab? You will need 3 inches of gravel under a concrete slab that is 4 inches thick. More gravel is better, but 3 inches is the minimum amount of gravel you should have with a 4” slab. Use ¾” washed and screened gravel, then compact it to level.
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.
Formula for Needed Crushed Stone
Multiply the length (L), in feet, by the width (W), in feet, by the height (H), in feet, and divide by 27. This will tell you how many cubic yards of crushed stone you need. When using this equation, make sure all of your measurements are in feet.
Having a gravel layer helps keep the slabs even, prevents cracks, helps with water drains and helps avoid low spots within the subgrade. The subbase is literally the foundation and with it, you don’t have to worry about the subgrade material.
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.
Rebar is not necessary for every concrete project. The general rule of thumb is that if you are pouring concrete that is more than 5 inches in depth, you are probably going to want to add in some rebar to help reinforce the entire structure.
A typical 24×24 garage slab costs between $3,057 and $5,944 with prices ranging from $5.31 to $8.31 per square foot for a 4” reinforced slab of concrete, and $6.83 to $10.32 per square foot for a 6” slab of reinforced concrete.
A rule of thumb for many crushed stone projects is to have a minimum depth of 2 to 4 inches, although some projects require more. For example, a patio that’s 12-foot square, with a 2-inch base of crushed stone, will need 0.89 cubic yards.
|Material||lbs./ cu. yd.||tons/ cu. yd.|
|Concrete, trap rock||4185||2.09|
Using 2 inches for the depth, the following measurements are a guide to the amount of gravel coverage per ton: 1/4 to 1/2 inch gravel, 100 square feet per ton; 1/2 to 1 inch gravel, 90 square feet per ton; and 1 1/2 to 2 inches gravel, 80 square feet per ton.
This ensures that water is taken away from the foundation. The material still needs to be compacted in order to reduce settling that will occur over time. The top 6 to 12 inches of the backfill under the slab should be filled and compacted with well-graded gravel or crushed material.
If you are compacting road crush with a vibratory plate you will get about 10 to 15% compaction. (This is based on you having a stable compacted base first. If you are putting the road crush on top of top soil you will lose more to compaction.) If you use a jumping jack, about 20% would be accurate.
Long story short, yes you can pour concrete over dirt.
Considering the support constraint, rebar is undoubtedly stronger than wire mesh. Several constructors consider rebar for domestic jobs. For thicker driveways and locations that involve greater traffic, rebar is always a good option to consider.
Too little water will make the cement crack, but too much makes it soupy and it won’t stay on the wall. You just have to work at it, until it feels right. Eventually you will get the hang of it. Plain old one-inch chicken wire is all you need for the reinforcing mesh.
RE: Too much rebar
The only case where this could have been “too much rebar” is if it resulted in an inability to consolidate the concrete sufficiently.
Foundations vary in design and materials, so costs vary greatly. An average home is about 2,000 square feet and a foundation can cost from $13,000 (including materials, labor and permitting) to more than $40,000 if it’s a basement foundation.
A 24×30-foot slab covers 720 square feet. With an average price of $6 per square foot, you may pay about $4,320 for a slab foundation. However, the price can range from $4 to $8 per square foot, resulting in a total cost between $2,880 and $5,760.
Regarding this, “how many bags of concrete do I need for a 10×10 slab?”, at 4 inches thick, generally you will need approximately either 74 bags of 60lb or 56 bags of 80lb premixed concrete for a 10×10 slab, at 5 inches thick slab, either 93 bags of 60lb or 70 bags of 80lb premixed concrete are required, while at 6 …
Try and wait for the ground to dry if it is a little wet before compacting, but if its unavoidable, add a small amount of large gravel to help bind the wet surface and continue compacting.
Dump Trucks: If you’re having the material delivered, a small dump truck usually carries about 5 cubic yards, and a larger one carries about 10 cubic yards or more.
|Material (1 yd3)||Density Estimate||US tons|
|Concrete||140 – 150 lb/ft3||1.89 to 2.03|
|Dirt||65 – 80 lb/ft3||0.88 to 1.08|
|Gravel (loose, dry)||75 – 95 lb/ft3||1.01 to 1.28|
|Gravel (dry 1/4 to 2 in)||105 lb/ft3||1.42|
A ton of gravel will cover approximately 100 square feet, 2 inches deep.
The formula: Number of Cubic Yards = Length (in feet) Width (in feet) Depth (in feet) ÷ 27. Simply multiply the three dimensions together to find the number of cubic feet, then divide by 27 to find the number of cubic yards.
Stone by the Ton
One Ton of Stone Cover in Square Feet240 sq. ft. One Ton of Stone Cover in Square Feet120 sq. ft.
While discussing our project with local excavators, several mentioned that they commonly include 4 to 6 inches of crusher run gravel UNDER the footings – properly compacted, of course – to improve forming and pouring of the footings. …
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