produced is comprised predominantly of gypsum together with small amounts of calcium phosphate and remaining calcium carbonate it will be appreciated that calcium phosphate and calcium carbonate are relatively insoluble thus allowing for a long life for the foamed plaster one advantage of the present invention is that the phosphoric acid used during formation of the foamed plaster forms an insoluble iron phosphate coating on any steel sheeting or reinforcing used in connection with the foamed plaster it will be appreciated that the use of other acids may cause degradation of steel in contact with the foamed plaster a further advantage of this method is that it is anticipated that over time the calcium phosphate will react with fluoride and or chloride in the resultant foamed plaster to form apatite making the structure stronger and with potentially soluble fluoride and chloride converted to relatively insoluble apatite it will be appreciated that the method described hereinabove may be varied by the addition of stabilising or strengthening elements to the plaster mix such as cement or other pozzolanic materials or organic polymers epoxies and the like it will also be appreciated that the amount of foaming and the size of the gaseous bubbles may be controlled by careful selection of the sizing and amount of calcium carbonate phosphoric acid and frothing agents used in the above process it is anticipated that a quantity of calcium carbonate between 2 and 12 by weight of the plaster of paris will yield a useful result in another embodiment of the invention foamed plaster blocks may be formed by combining the equivalent of.