A similar method is used by building conservators to help support
'important' plaster which has come adrift. It is not especially
successful in my experience but worth a try. Make a drain hole at the
bottom so with luck you can see when the excess fluid starts to come
out.

Start by wetting the space with water (+a dash of soap to make it
wetter) first otherwise it will be so dry that the pva won't spread.
Make the pva mix very watery too. One of those flexible syringe
extenders helps to spread the liquid around

Anna
--
~~ Anna Kettle, Suffolk, England
|""""| ~ Lime plasterwork, plaster conservation
/ ^^ \ // Freehand modelling and pargeting
|____| www.kettlenet.co.uk 07976 649862