How to Build a Cinder Block Porch

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Cinder blocks are much like concrete blocks. They are the same dimensions, nominally 8 inches, but actually 7 5/8 by 16 inches. Concrete blocks are made with cement, sand and fine gravel. Cinder blocks use coal cinders and ashes with cement. You can use either in some building projects -- cinder blocks tend to be lighter and perhaps less durable. You could use cinder blocks to build a porch, either as an addition to a house or as a replacement for an existing porch which has deteriorated.

Things You'll Need

  • Measuring tape
  • Stakes and builder's twine
  • Shovel or excavating tool
  • Cinder blocks -- full size and half block (optional)
  • Mortar
  • Trowel
  • 2-by-4 board
  • Level
  • Concrete (optional)
  • Form, lumber or metal (optional)
  • Concrete finishing tools (optional)
  • Lay out the dimensions of your cinder block porch on a sheet of graph paper to determine how many blocks you will need. For a 12-foot by 16-foot porch, you will want a perimeter wall nine blocks deep by 12 blocks wide. You can make it just one block high or more, depending on how high you want your porch to sit (for a 2-foot porch, you will need it to be three blocks high). Mark the area with stakes and builder's twine, adding 8 inches all around for footings. Then buy your blocks; some building supply stores deliver.

  • Excavate the area. Remove all the dirt at least 8 inches deep inside the porch area and dig a trench for your perimeter that is at least 8 inches deeper than the inside and 12 inches wide. Pour concrete into your trench for footings. For this type of wall, you probably will not need to build forms, although that is an option. Your footings should be 8 inches deep and 12 inches wide. Let the concrete sit at least a day before proceeding. Place stakes and twine around your perimeter as squaring and leveling guides. Make sure corners are square and string heights are correct.

  • Lay your perimeter wall, setting blocks in mortar on the concrete. Start at the house side and move outward, following your guidelines. Spread mortar on the concrete with a trowel and set blocks into it; "butter" the ends of blocks with mortar as you lay them to seal joints. Use a level to make sure blocks are level. If you are laying more than one course high, stagger the joints so the blocks overlap each other. If laying more than one course, use a level to make sure the blocks are straight and plumb.

  • Fill the interior of your perimeter with gravel and sand. Lay 4 to 6 inches of gravel and compact it with a hand or mechanical tamper (it's best to lay in courses, 2 to 3 inches and tamp, then the rest of the gravel). Make sure it is solidly compacted and fairly level. Then add 1 to 3 inches of sand, to bring the interior up to the level of your perimeter wall. Compact the sand with a tamper; level it with the top of your perimeter wall by running a 2-by-4 board across it.

  • Deck your cinder block porch. You have two options: you can lay half-blocks (4 inches high) on top of your sand and perimeter wall, mortaring the outside blocks onto the perimeter blocks; or you can build a wooden form and pour concrete to fill the interior. If you opt for concrete, use 2-by-4 boards held by stakes to make a barrier around the outside edge of the perimeter wall, then fill the space with concrete (it will flow into the gaps in the tops of the blocks but that will just solidify your perimeter wall). Finish your concrete with concrete finishing tools. If you opt for a block deck, lay blocks across the wall top and sand to cover the area, then sweep dry mortar to fill the crevices between the blocks. You can then sprinkle with water to set the mortar.

Tips & Warnings

  • For a really simple and small cinder block porch, excavate an area about 8 by 10 feet, about 8 inches deep. Then fill the area with compacted gravel and sand and place blocks in it, resting on the sand and butting firmly together, smooth sides up. Then sweep dry mortar into the joints to seal it. You can fill block gaps on the sides with concrete to finish it.
  • Use caution lifting and carrying blocks; a dropped block can crush a toe.

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