HPMC stands for Hydroxypropyl Methyl Cellulose, which is a commonly used additive in building materials such as mortar and grout. It is used as a thickener, water retention agent, and to improve workability and adhesion of the material.

EIFS stands for Exterior Insulation and Finishing System, which is a type of exterior wall cladding system that provides insulation and weatherproofing to a building's exterior. It typically consists of a layer of insulation board, a base coat of adhesive mortar, a reinforcing mesh, and a finish coat of colored and textured stucco or acrylic.

When used in EIFS mortar, HPMC can help to improve the workability of the mortar, making it easier to apply to the insulation board and reinforcing mesh. It can also improve the adhesion of the mortar to the board and mesh, ensuring a strong and durable bond. Additionally, HPMC can help to reduce the amount of water required in the mix, which can help to prevent cracking and shrinkage in the finished EIFS system.