Foundation underpinning repair

Written by ben wakeling
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Foundation underpinning repair
An insufficient concrete foundation can crack under the weight of the building. (Jupiterimages/Photos.com/Getty Images)

If a foundation is damaged, cracked, or unable to take the weight of the building above it, it can sink and move in the earth, causing serious structural damage to the building. One way of shoring up a foundation is to underpin it, which means increasing the strength of the existing foundation. This is a difficult and very dangerous task, and must only be carried out by an experienced contractor.

Skill level:
Challenging

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Things you need

  • 4 solid concrete blocks
  • 3 adjustable jacks
  • Utility chisel and hammer
  • Needle beam
  • Reciprocating saw
  • Concrete blade (for the saw)
  • Shovel
  • Masonry wedges
  • Concrete
  • Concrete mixer
  • Steel plate, 6 inches by 4 feet

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Instructions

  1. 1

    Cut a hole through the bottom of the wall you are shoring using your hammer and chisel. Make sure the hole is large enough to insert a needle beam through the wall horizontally. Make sure you use the jacks to support both ends of the beam to take the weight of the wall.

  2. 2

    Excavate the earth under the wall section you have just removed with a shovel. Make sure you do not dig beneath the supporting jacks. Only dig deep enough to reach the base of your new foundation.

  3. 3

    Install your new foundation using known data regarding the strength of the soil. This can be a micropile, but most often it is simply a case of filling the void you have just dug with concrete.

  4. 4

    Slowly transfer the load of the cement wall to the new foundation by placing a jack between your new foundation and a steel plate, under the wall you are shoring.

  5. 5

    Transfer the load of the wall away from the jack by inserting masonry wedges between your new foundation and the wall you are underpinning. Take away the jack and fill the space left behind with concrete.

  6. 6

    Continue Steps 1-5 in an adjacent section of wall, and continue until the entire length of the wall you are shoring is underpinned.

Tips and warnings

  • Wait for each section of new concrete to cure before moving on to the next. This takes 28 days.

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