How to Install PVC Plumbing Pipes Below the Basement Floor

Digging the Pipe Trench

• 1

  Use chalk to mark the path that you need your pipe to take onto the floor. Keep the line as straight as possible to keep the number of joints installed at a minimum. Place two cutting lines onto the floor bracketing the path line. Make the cutting lines parallel to one another with the space between them equal to the diameter of your pipe plus 12 inches. This will give you space to dig and plant the pipe in place.

• 2

  Put on protective gear for cutting through the basement floor. You’ll need safety goggles, heavy work gloves, steel-toed boots, and a particle mask to deal with both flying concrete chips and dust. Open any windows and doors to the room to help with ventilation.

• 3

  Test the depth of the slab by drilling through it somewhere along the center path line with a hammer drill containing a masonry bit. Push a steel rod through the slab after drilling through it until you hit the resistance of the soil beneath the slab. Put a mark on the probe with the chalk, and then pull it from the floor. Measure the depth of the slab with a tape measure from the base of the probe to the mark to determine slab depth.

• 4

  Cut the basement slab along the parallel cutting lines with a walk-behind concrete saw. Set the saw for the measured depth of the slab. Move the saw to the start of one of the cutting lines and line up the saw blade with the chalk line. Start up the saw, and then push the blade along the line, cutting through the basement slab and any rebar contained within the concrete. Repeat the cut along the second cutting line running parallel to the first.

• 5

  Cut perpendicular lines through the concrete between the two cut lines that you just made, spaced every 10 inches.

• 6

  Break the concrete between the cut lines with a sledgehammer, aiming the blows at the perpendicular lines running along the length of the cuts. Remove the debris from the area to access the soil beneath the basement.

• 7

  Dig a trench for the PVC pipes along the cutout concrete length using a trench spade. Use the width of the cutout area to determine the width of the trench, and dig to a 12-inch depth plus the diameter of the pipe if placing a pipe that will not move pressurized liquid, or a depth 18-inches plus the diameter for a pipe that will be pressurized. Tamp down the base of the trench with a tamper to create a solid surface for laying the pipe.

Pipe Assembly and Installation

• 8

  Assemble the pipe on the basement floor by gluing sections of the PVC together using couplings where needed to connect them. Clean the outside of the pipe ends and the interior of couplings with PVC primer to the point where the two pieces fit together. The primer will soften the pipes as well, making them fit more securely. Apply a layer of PVC solvent cement to the cleaned area, and then push the pipe and coupling together. Hold the connection together for 30 seconds to bind the two together. Make sure you place a fitting that connects a pipe leading from the trench bottom to above the basement surface on the end of the pipe.

• 9

  Cut the PVC pipes where necessary with a hacksaw. Deburr the cut end of the pipe by scraping the interior and exterior of the cut end with a utility knife.

• 10

  Lower the pipe into the trench and then connect it to whatever external or internal pipe you need to connect it to. You can continue digging your trench under the wall to the outside beneath the house foundation if needed.

• 11

  Cover the pipe with soil once entrenched, until you reach the level of the base of the concrete slab. Brush the sides of the concrete trench with bonding adhesive. Place rebar chairs along the base of the trench sized to raise rebar to the halfway height of the basement slab, in two parallel lines running equidistant down the center of the trench. Place a rebar down each line of rebar chars, sitting on the chair tops.

• 12

  Mix a fresh batch of concrete in a wheelbarrow with a hoe. Pour the concrete into the trench over the rebar and around the protruding PVC pipe until you reach the level of the basement floor. Trowel the surface of the concrete level with the floor level and leave it to cure for 10 days.