How do you prepare a concrete base?

What is the correct mix for a concrete base?

A standard concrete mix ratio of 1 part cement to 5 parts ballast (aggregate and sand) is usually perfectly adequate for shed bases but you can add reinforcing fibres if you are housing anything particularly heavy.

Can I pour concrete directly 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.

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.

How to Lay a Concrete Base Part One

Do you need a subbase for concrete?

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 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 pour concrete over grass?

Cheap and versatile and easy to pour, concrete will last you years down the road. You can pour it just about everywhere—including on the grass. Although it takes a little work, pour concrete over grass to create that walkway you always wanted or that mowing preventative you could previously only dream about.

How deep should a concrete base be?

Preparing the ground

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. Slabs intended for commercial use should be at least 175mm thick and reinforced.

Can I use building sand for concrete?

Building or soft sand should not be used in concrete, as the grading is finer than concreting fine aggregate and leads to increased water demand. It is usually used for mortars and renders.

Can I mix cement with sand only?

Can I make concrete with just sand and cement? No, you can't make concrete with only sand and cement. Concrete isn't considered concrete without aggregates like gravel and stone. It's the aggregates that contribute to concrete having high strength.

What kind of plastic goes under concrete?

The most commonly used vapor barrier under concrete slabs is polyethylene (poly) plastic sheeting with a thickness of 10 mil or 15 mil.

Do I need black plastic under my concrete slab?

No. You don't “need” a vapour membrane under a shed concrete slab but it is still a good idea to install one. It is still a good idea to have protection against rising damp even though you don't strictly need it.

How do you insulate a concrete floor before pouring?

Can I pour concrete over gravel?

Cement mix might work in some cases over an existing gravel driveway. Laying a concrete driveway over an existing gravel one is possible, but it is not generally recommended. The kind of gravel that is intended to go under cement is typically a smaller grade than what is used for gravel driveways.

Can you pour concrete over rocks?

Big rocks are not a problem as long as there is uniform concrete coverage and adequate rebar for temperature fluctuations. If the big rocks protrude up above grade and if you have a few in a row, it will weaken the slab. We like things uniform, including the grade, thickness of the concrete, etc.

Can you pour concrete directly on sandy soil?

Failing to Prep the Site

If you're lucky enough to have sandy soil in your yard, you can simply remove the grass and topsoil and pour a layer of gravel for extra drainage. Make sure the surface is firm and level before you start pouring concrete as well.

How many inches of gravel do you need for 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.

How thick should a concrete slab be?

Standard concrete floor slab thickness in residential construction is 4 inches. Five to six inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks. To prepare the base, cut the ground level to the proper depth to allow for the slab thickness.

How much sand and gravel do I need for a yard of concrete?

An average 1:2:3 mix contains one part cement, two parts sand and three parts gravel. To make 1 cubic yard of concrete, you'd need seven 94-pound bags of cement, about 1/2 cubic yard of sand and just over 3/4 cubic yard of gravel.