It is well known that poly-carboxylic acid materials, such as polyacrylic acid can be cross-linked to form a solid cement by treatment with divalent or polyvalent metal ions. Typically the metal ion comprises zinc and or calcium. Recent work has shown that the metal ions required for cross-linking such cements may be supplied by glass compositions which may or may not completely dissolve in water as the cement sets.
When preparing water setting cement compositions in which a glass material provides the cross-linking means two stages of setting of the material are observed. During the first stage the viscosity of the aqueous mix increases rapidly, but during this period the mix has little rigidity and can be stirred, poured, cast or otherwise worked to give a desired shape of the first product. The onset of the second setting stage is indicated by gelling of the mix at which point the material has sufficient rigidity to prevent further working. During the course of the second stage the material develops greater mechanical strength. The end of the second stage may be arbitrarily defined as the time at which the cement has sufficient rigidity appropriate to a particular use. The two periods of setting are known as the working time, t.sub.w, and the setting time t.sub.s. It has been found that the setting characteristics are determined by the particular glass composition employed to effect cross-linking of the poly-carboxylic acid material and that furthermore, the period between gelling and setting of the material in general corresponds to the period within which gelling occurs.
In many applications it is necessary to provide a cement having a relatively long period before gelling occurs so that ample time is provided for making the material. However, in providing a long working time, the period between gelling and setting is correspondingly extended and in many circumstances is excessive.