Concrete Pre-Pour Pan Checklist for Decks

Gravel Layer

• The base layer of gravel that goes down before anything else is vital to the overall security and stability of the concrete for your deck. The gravel goes on top of the dirt in the excavated area and acts as drainage for water from rain and soil. If there is not a layer of compacted gravel in place to facilitate drainage, the soil will retain water, which then freezes. When water freezes, it expands and pushes upward, which can force the concrete to buckle and crack out.

Sand Layer

• On top of the base layer of gravel is a compacted layer of sand. This is the compression level of the overall concrete structure. Sand helps the concrete compact slowly over the years, rather than suddenly, all at once. Concrete slabs weigh thousands of pounds; and if the weight isn’t distributed evenly and allowed to settle into the earth slowly, it will shear off, and one section will drop more rapidly than another. This will create sections of concrete where the slab is broken off and lower than elsewhere.

Inclusion of Metal

• Knowing whether or not to include metal supports within your concrete is a decision that only a structural engineer can make. For example, typical driveways, patios and decks that are only 4 inches thick do not necessarily need to have rebar or metal included within, but the only person who is qualified to make that decision is a structural engineer. If your deck will later on have walls with a roof above, you will need to include some type of support within the concrete to strengthen it.

Framing

• Another important aspect to setting up a poured concrete structure is the frame. Since concrete needs some form of framing in place for the initial 24 to 72 hours to keep the concrete from slagging out during its curing phase, you must have solid framing. This can be wood or metal, depending on the environment and the conditions that your structural engineer sets down for the safety of your pour. For decks, this is most commonly wood.