Preparation of hydroxyapatite coating for the conservation of gypsum crust on historic limestones

An artificial hydroxyapatite coating was prepared on gypsum crust for the purpose of conservation. It was done by successive introduction of calcium and phosphorus sources into the crust by surface permeation. both surface protection and integral consolidation of the gypsum crust can be accomplished by this method. It would be a good solution for the conservation of the gypsified historic limestone surfaces. [Display omitted] •Hydroxyapatite coating was prepared for the conservation of calcareous relic.•No soluble salts were introduced and the preparation method of the coating was safe.•Both surface protection and integral consolidation were accomplished by this method. A new preparation method of hydroxyapatite coating was proposed for the conservation of gypsum crust on historic limestones. by successive introduction of calcium and phosphorus sources into the crust by surface permeation. Due to the formation of hydroxyapatite coating, both surface protection and integral consolidation of the gypsum crust can be accomplished. The performances of the hydroxyapatite coating were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry, water stability, capillary water uptake, color difference and adhesion strength test. The experimental results indicated that the hydroxyapatite coating would be a good solution for the conservation of the gypsified historic limestone surface.