If you should see a crack in your basement floor, walls or ceiling; the understandable reaction is to set about repairing it. However, before setting about doing a DIY basement crack repair you might want to establish how serious the crack is.

A crack that appears in your basement could just be due to something heavy being dropped on the basement floor or shrinkage due to drying out of some plaster-work. Unfortunately it could also be symptomatic of something more serious and require monitoring before repairing.

Causes of Basement Cracks

As stated above a crack appearing in a basement could have an entirely simple explanation to it. However, the cracking could also be due to either subsidence - the movement of land around or underneath the building, or settlement - the movement of the building as it ‘settles’ on its foundations.

Settlement is not particularly unusual and is rarely serious. However, subsidence can be very serious requiring remedial work to be done on the foundations of the building. Regardless of the cause of the cracking you’ll want to make sure it’s not going to re-open or get worse after you’ve done your DIY repair in the basement.

Monitoring

You can buy crack measuring gauges to monitor the behavior of the crack. These are simply two plates; one plate has calibrations on it and the other horizontal and vertical guide lines. By positioning the gauge over the crack and zeroing the plate’s alignment you can see if the guide lines move from zero over a period of time. When the crack stops expanding - that’s the time to carry of your DIY repair to the basement crack.

Hoping that your crack hasn’t got an underlying serious problem behind it, here are some tips about making a DIY repair to basement cracks.

Repairing a Crack in Concrete

Chip along the length of the crack with a hammer and cold chisel to form a ‘V’ shaped groove about 25mm wide. Brush out any loose material then brush along the newly exposed surface with a PVA bonding agent; this will increase the bonding properties between the old and new concrete.

Whether you decide to mix your own concrete or buy a bag of pre-mix doesn’t matter, but when mixing it with water add some of the PVA bonding agent to the mix, as recommended by the manufacturers instructions. Pack the new concrete into the groove, making sure to fully fill all of it, and then finally smooth the concrete level with a trowel or float.

Repairing Cracks in Basement Plaster

Cracks in plasterwork can be simply filled using any of the proprietary plaster fillers. Using a scraper or palette knife scrape away any loose material, when doing this it’s a good idea to make the crack a little deeper to help provide a ‘key’ for the filler.

Brush away the loose debris and wet the area to be treated with water. If necessary mix the filler and place it on a bat, using the scraper or palette knife press the filler into the crack so that it is slightly proud of the crack.

After about 24 hours the filler will have dried and you can use a glass-paper to rub the area down so that it’s flat with the original plaster work.

Repairing Brick Wall Cracking

If you’ve got cracking in the mortar of a basement brick wall you could have a subsidence problem; and it might be advisable to get some expert advice. However, if the cracking is due to settlement it’ll be fine for you to carry out a DIY repair to the basement crack.

First use a joint raker to remove the old mortar, any difficult bits might require you to use a hammer and cold chisel on them.

Brush out the area you’ve worked on to remove all the dust and debris, then wet the area to be treated with water. After mixing your mortar apply it with a pointing trowel and use a brick jointer to match the finished profile to the old mortar.

Finally remove any excess mortar with a small dry and stiff brush. NB. If settlement was the cause of the cracking you could alternatively use special ‘stitching rods’ with an epoxy resin, rather than the traditional mortar replacement method.