Wallpapers, paints and other finishes can spoil the appearance of plaster surfaces and may trap moisture. Where the bond with laths has failed, reinforce by pouring fresh plaster from above and strengthening with a jute scrim set into this and secured to the joists.Always use screws for any fixings to avoid vibrations to fragile ceilings.Investigate from above if access is available from a loft or by carefully lifting floorboards.Problems with ceilings frequently result from the plaster bond having failed, structural movement, failure of joists, damp problems and rotten or beetle-infested laths. Removing a loose section of old lime plaster Mending sagging or cracked ceilings Alternatively, gypsum may sometimes be added to a lime plaster mix for the same purpose. To patch repair plasterwork, slightly treat the exposed edges of the existing plaster with water or diluted PVA (one part to 10 of water) to control suction and prevent cracking.Cracks and pockmarks may be filled using matching plaster, or narrow ones with proprietary interior filler gauged with whiting.Make necessary repairs with appropriate traditional materials.Consult a structural engineer if in any doubt.Monitor cracks over a period of time by marking and dating their end point on the wall.Investigate bulges or anything larger than a hairline crack.Rake out thin cracks and fill with a good filler.Some cracks and bulges in plaster may be superficial or localised others result from failure of the masonry or timber beneath, or may indicate wider structural problems within the building. Inappropriate modern plasters and finishes.DIY: Make plastering walls an easy job with our guide.Rotten laths can result in plaster sagging or bowing. In the case of stud walls and ceilings, timber laths are fixed between the studs or joists and the plaster is pushed through the gaps between the laths.

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