I ve been trying to fill a small but deep crack in a wall but just when I think I ve got it right the filler collapses inwards. What am I doing wrong

A.� The problem is that although the top layer might look dry and flush what's behind is still wet and hasn't filled the gap, so that when it comes to sanding or painting the whole lot ends up collapsing into the gap. You need to fill it bit by bit. Start with a thin shallow layer inside the cavity and then let it dry. The second layer than has something to grip onto. It may take a third application to get enough filler in there for it to come flush with the wall.

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A.� That's usually because the plaster is loose and crumbling and simply comes away with the filler. Try wetting the loose plaster using a mist sprayer to temporarily bind it together just before applying the filler.

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A.� These are awkward for two reasons; they are often deep and also filler finds it difficult to defy gravity without anything to adhere to. Stuff the hole with a bit of scrunched up newspaper, which not only fills much of the space but also gives the filler something to hang on to. In this case it is best to use ready mixed filler rather than one you've mixed yourself to ensure it is thick enough not to sag.

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A.� That depends. For frequent small jobs around the house the ready mixed fillers save time and should be at exactly the right consistency, as long as you don't let them dry out by not sealing them properly. If you've got a large area to cover which is liable to need more than one application it is much more economical to buy a bag of bonding plaster from a builders merchant and mix it according to the instructions.

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A.�� As long as it is only a relatively small area, above the skirting board for instance, there is no reason why you can't do it yourself and save a bit of money. It just needs a bit of careful preparation and patience.

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