Conservare Hydroxylating Conversion Treatment (HCT) is a novel, two-component, waterborne treatment which protects and strengthens deteriorating carbonate building stones such as marble, limestone, dolomite and travertine. HCT (patents pending) forms a stable, well-adhered, hydroxylated, conversion layer on carbonate mineral grains. This conversion layer dramatically increases the resistance of marble and limestone surfaces to acid attack, and improves the ability of a variety of chemical compositions to react with or bond to such surfaces.