Please choose the correct ending to complete the given sentence: Computers and Electronics: [header] How to tamp concrete [title] Build a formwork for your concrete surface. [step] Before you begin tamping or even pouring the concrete, you'll need to have forms in place. Nail together a series of boards to fit the area you'll be concreting, dividing the different sections as needed.

Ending1: Trace the lines of the forms together using a landscape ruler or pencil to create the trowel lines. [substeps] Polyurethane or kevlar is a weak material, but for concrete that's not waterproof, use a moisture-retaining compound like sandstone. Ending2: [substeps] You can find formwork templates at a hardware store or online. [title] Break the concrete into blocks and joints. Ending3: When you run out of boards, lay a tarp down to protect the concrete rather than covering it completely. [substeps] Use drywall screws to secure your forms in place. Ending4: Use a level to make sure the surface comes out perfectly flat. [substeps] Formwork structures serve to mark the perimeter of the concrete surface and contain the wet concrete mix while it's being spread and compacted.

Answer format: ending1/ending2/ending3/ending4