Methods of sealing a wellbore include sequentially displacing a first sealant composition and a second sealant composition different from the first sealant composition into the wellbore, followed by allowing the first and second sealant compositions to set. In an embodiment, the first and second sealant compositions are pulse injected into the wellbore. The first and second sealant compositions may be arranged in an alternating, stratified pattern in the wellbore. A mechanical property of the set first sealant composition and the same mechanical property of the set second sealant composition have substantially different values. As such, an impermeable, stratified structure comprising the set sealant compositions is formed that may resist failure when at least one of them is subjected to a mechanical stress.