The ownership of improvements, whether for utility or adornment, made on the separate property of the spouses at the expense of the partnership or through the acts or efforts of either or both spouses shall pertain to the conjugal partnership, or to the original owner-spouse, subject to the following rules:
When the cost of the improvement made by the conjugal partnership and any resulting increase in value are more than the value of the property at the time of the improvement, the entire property of one of the spouses shall belong to the conjugal partnership, subject to reimbursement of the value of the property of the owner-spouse at the time of the improvement; otherwise, said property shall be retained in ownership by the owner-spouse, likewise subject to reimbursement of the cost of the improvement.
In either case, the ownership of the entire property shall be vested upon the reimbursement, which shall be made at the time of the liquidation of the conjugal partnership. (158a)