Concentrated sodium silicate solutions of modulus (SiO2/Na2O molar ratio) close to 1.0 are well-known to precipitate hydrous sodium metasilicate crystals; this hinders their industrial-scale utilization in applications including geopolymer concrete synthesis. The substitution of 20-50% of the sodium by potassium in such solutions is seen to greatly reduce or prevent this precipitation, on a time scale of up to 7 years. A potassium substitution rate of 20% does not entirely eliminate precipitation, but does reduce it very significantly; 50% substitution does eliminate precipitation, although the viscosity of the solution increases notably at this level of substitution. This substitution provides a relatively low-cost means of extending the shelf life of concentrated low-modulus alkali silicate solutions for large-scale utilization in the production of geopolymer concretes and in other applications.