Repairing a Large Crack in Plaster


Plaster walls in older homes often fall prey to cracks and other unflattering defects such as, uneven texture and pitting. Not only does this give a shabby, dilapidated look to your home, the crack could widen over time and leave a much bigger area of plaster vulnerable. Even If you simply fill the cracks with joint compound or Polyfilla, more than often they are prone to propagate back through. To really solve this dilemma, special self-adhesive glass fibre mesh drywall tape can be applied over the crack for extra reinforcement.

You might think patching large holes and cracks in plaster is a piece of cake, that is until you’re faced with the conundrum of matching your repaired patch to your walls. The aesthetic appeal is one of the trickiest parts to get right. You don’t have to fret so much if your walls are smooth, but those with textured walls you need to match the artistic detail within them as well. However, before getting down into the nitty gritty details, you need to think about patching up the cracks:

bottle opener
N.B: A cheap metal bottle opener is pretty handy to get the job done quickly. Even if you don’t have one, go get one before starting!
  • Neatly undercut the crack with a point-ended bottle opener, screwdriver or other pointed tool to open up a greater area for the infill material to sit. This helps the plaster to bond as the undercutting creates a slight lip in the plaster just underneath the surface. Brush or blow out any debris or dust, and dampen the crack with a sponge.
  • Next, fill the crack half-full with patching plaster using a putty knife. Wait until the plaster crater is thumb-print firm, then key the surface with a nail tip to give the next layer something to cling on to. Let it dry completely.
  • After the plaster has dried up, dampen the set plaster lightly and stuff another layer into the crack, leaving a 3mm to 6mm valley from the surface.
  • In order to blend the area into the surrounding wall, allow the patching plaster to dry completely before slathering the visible finishing plaster over the crack. The finishing plaster should then fill the crack completely. Use s straight edge, such as a wide putty knife, to level the plaster with the rest of the wall. To get a smooth, even finish, dip the straight edge in water. For textured walls, it is a good idea to employ the edge of a smaller putty knife. You can even cut a piece of cardboard to the dimensions of the widest part of the crack. The trick is to drag the surface only across the crack to smooth out the plaster, steering as far away from the original textured surface as possible!

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