Patching Large Cracks
Patching Large Cracks And Holes
Filling in large cracks and holes is multi-step process.
1. Fill in gap half-way with patching plaster
2. Fill in gap again with patching plaster
3. Finish filling in gap with finishing plaster
4. Match wall texture
5. Prime and paint
Patching large cracks and holes is a fairly easy process until you get down to matching your walls. The cosmetic aspect is easily the trickiest part. If your walls are smooth, your worries are few. Those with textured walls will need to appeal to the places within them that are artistic. In some of us those places are buried quite deep indeed. But first let's deal with the easy part.
Once again, you'll find it handy to have one of those gas-station-quality metal bottle openers to aid you in this job. If you haven't got one (you probably threw it away when you got that deluxe cabinet-mounted one three birthdays ago), then make a nuisance of yourself and ask your neighbors; someone is bound to have one lying about. Just don't mention what you intend to use it for and wash it off before you return it.
1. Make a hospitable environment for new plaster by "undercutting" the crack with a point-ended bottle opener. Undercutting creates a tiny lip in the plaster just beneath the surface, which will help the new plaster to bond. Blow or brush out any dust or debris. Dampen the crack lightly with a sponge.
Tip: Some plaster crumbles easily. If your plaster is prone to crumbling, or if you have trouble getting the hang of undercutting, skip it. Your wall will accept the new plaster without it, as long as the edges are clean of debris.
2. Use a putty knife to fill the crack half-full with patching plaster. Once the plaster crater is thumb-print firm (but not hard), score it with a nail tip so the next layer will have something to cling to. Let dry completely.
3. Once it's dry, lightly dampen the set plaster and spread another layer of patching plaster into the crack. It should not quite fill the crack (leave a 1/8 to ¼ inch valley).
4. Once the patching plaster is completely dry, you're ready to apply the visible finishing plaster to blend the area into the rest of the wall. Apply the finishing plaster to the crack to fill it in completely. Use a wide putty knife or other straight edge to level the plaster with the rest of the wall. Then dip the straightedge in water and do it again to get a smooth finish. If you have textured walls, it is helpful to use the edge of a smaller putty knife, or cut a piece of cardboard to the width of the widest part of the crack. Drag it only along the crack to achieve a level surface, avoiding as much textured surface as possible.
Tip: It is better to have a slight indentation in your patch than an over-full mound. Filling in to a level point is infinitely easier than sanding down a mound. It is better to do several thin layers than one heaping application.
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