How deep should a sub-base be for a concrete slab?

A flat base course will also allow the slab to slide easily as it shrinks, reducing restraint and the risk of cracks as the concrete contracts after placement (drying shrinkage). The entire subbase and base system should be at least 4 inches thick—thicker if the engineer feels it is needed for proper support.

How much subbase do I need for a concrete slab?

As a rule; your base must be 75mm larger that the finished slab to allow for formwork. Clear the area of stones and plants and excavate to a minimum depth of 100mm (deeper for soft ground). The ground should be levelled and well compacted using a small garden roller or a lump hammer to provide a base for your concrete.

Do I need a sub-base for a concrete slab?

Subbase for Concrete Slab

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. As the thickness of subbase increases, the ultimate load carrying capacity of slab increases.

What is the best sub-base for concrete slab?

The best sub-base for a concrete slab is gravel. The soil has to be prepped first before the gravel can be laid down; pouring concrete directly onto rock is not considered a best practice. You can use different kinds of gravel for the subbase as long as it is clean and uniform in shape and size.

How deep should fill material be to create an adequate subgrade for concrete?

Make sure that you level the backfill to a uniform depth of at least four inches.

Concrete basics for Beginners from top to bottom, ground prep, rebar, sealing

How much subbase do I need?

Measure the length and width in metres of the area you wish to fill with a sub base aggregate e.g. 20m x 10m. Multiply the length and width to find the area in square metres. Multiply by the depth e.g. 150mm. Multiply by 2 to get the tonnage required.

What happens if you dont compact sub base?

Each time a vehicle pulls into a garage and stops, that action creates a plate compactor effect. If the backfill under the slab has not been properly compacted, the structural fill will eventually settle, leaving voids.

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 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.

Can I pour a concrete slab on dirt?

Long story short, yes you can pour concrete over dirt.

What happens if you don't 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.

Can I use sharp sand as a sub-base?

We recommend laying sharp sand to the thickness of 10/15mm . The sand is only there to blind the top of your sub-base, so it should be firm.

Can you use broken concrete as sub-base?

It will be fine.

How thick should my sub-base be?

How deep should my sub-base be? Generally, a flexible sub-base of unbound material needs to be at least 100mm deep, as does a bound sub-base of CBM/HBM. For bitumen-bound material, then 50mm is a typical minimum thickness.

How deep should type 1 be for a patio?

Once you are happy with the depth, you should lay a sub base material for example MOT TYPE 1 to a compacted depth of around 75mm. You will need take into consideration the fall when laying this. Check the surface is level with the top of the marker pegs and then again at the bottom.

Can I use gravel as a sub-base?

This unstable structure means all gravels are not suitable for patio sub bases. The typical reason for wanting to use gravel for a patio base is recycling existing materials. It is much more expensive to skip used gravel and buy in fresh sub base.

Do you need a rebar for a 4 inch slab?

For 4” concrete slabs used for driveways and patios, #3 rebar is common. Driveways that will support daily traffic by heavy trucks frequently use 1/2″ or #4 steel bar.

What kind of gravel do you put under concrete?

The base in concrete construction is usually a form of crushed stone. 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.

Can you leave concrete forms on too long?

In short, there is no such thing as leaving concrete forms on for too long, as they will simply continue the curing process as the forms remain in place. However, there is no real need to leave forms on for longer than necessary.

How thick should a concrete base be?

In general, 6 inch (150mm) slab thickness is considered for residential and commercial buildings with reinforcement details as per design.

Is sand a good base for concrete?

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.

Should I wet sub-base before compacting?

You'll want to ensure that the water penetrates the entire depth of the sub-base material from top to bottom, but you'll want to avoid flooding the surface. If the base is too wet, you'll find that your plate compactor sinks too deep into surface. If this is case, allow the aggregate to dry out.

Can you compact sub-base by hand?

Ideally a small wacker plate would be beneficial to compact it but a hand tamp will do an ok job although you'll have arms like popeye when you finish.

Can you compact without a compactor?

A lawn roller or hand tamper can be used to compact the moist soil, or you can walk over it.