When it comes to backyard sheds the 16'x20' shed is huge. It is large enough to do anything from storing a lawn mower to a small car. There are two main floor systems used for large sheds. These include wood and concrete with concrete being the most popular because it provides a floor that is dense and solid enough to hold almost any activity or storage need of the shed. Most 16x20 shed plans describe how to build the wood floor but they will not tell you how to pour a good concrete slab. This makes it important to either hire a reputable concrete flatwork company or to install the concrete yourself. Either way you need to make sure that the concrete is installed using the following tips.

Prepare The Ground: Preparing the ground that goes underneath is one of the most important steps to pouring concrete. The base under the slab must be compacted or undisturbed soil that has a gravel or road base layer on top of it to provide good drainage and a level surface.

Consolidate The Concrete: After setting up your forms and pouring the concrete close to the same height as the top of the forms you will need to consolidate the concrete by tamping down on the top of it using a concrete tamper. This brings the cream and air bubbles to the surface which makes it easier to finish.

Strike The Surface: The surface of the concrete is leveled using a long board that goes from one side of the slab to the other. A 16x20 foot storage shed slab should be divided into two slabs that are 8x10 to reduce stress on the slab and help prevent cracks. This also makes it easier to strike the surface because you can pour each side separately.

Level The Surface: Striking the surface with a long board makes the surface fairly level. To make it even more level you will use a long float called a bull float. It makes the surface even flatter and fills in most of the holes left by the long board used to strike the surface.

Wait and Watch The Surface Bleeding: As the concrete starts to set up it will "bleed". This means that moisture will come to the surface and puddle. It is important to stay off the concrete until this bleeding stops. Problems such as crazing, dusting, blistering or de-lamination are more likely if the concrete surface is worked before the bleeding stops. The waiting period varies depending on the air temperature, wind, surface under the concrete and the mix of concrete. The NRMCA states that the concrete will be ready to be worked if the footprint of a person sinks 1/8" to 1/4".

Install The Final Finish: Once the surface is ready to be finished you can trowel the edges, install any concrete joints and then trowel the surface with a magnesium trowel. If you want a really smooth finish you can go over the surface with a steel trowel after the magnesium trowel. Rougher surfaces are created by using a damp broom to lightly brush the surface after one pass with the magnesium trowel.

Curing The Concrete: Another of the most important steps to pouring concrete is the curing process. This step increases the strength of the concrete which is important if you are using your large shed to roll heavy equipment or cars on. The trick to properly curing concrete is to slow the moisture from leaving the concrete. About 12 hours after the pour spray the surface with a light mist of water and then cover the concrete with plastic. This keeps the water from evaporating. After a few days you can remove the plastic and seal the concrete surface with a quality sealing spray. This will help keep moisture inside the concrete during the month long curing process. If you are in a hurry to build your shed using your 16x20 shed plans you may want to get onto the concrete long before it is fully cured. It is typically ok to walk on poured concrete 24 hours after pouring and you can start framing on it but be careful because it is still soft enough to scratch.

Even if you hire out the concrete work for your 16x20 shed it is important to discuss with the contractor how the slab will be installed. Many installers do not use proper installation techniques because they take a bit more time and work or they simply do not know the proper steps. But as you can see using the proper finishing step are a critical part of shed building when you are building it with a concrete floor.