Synthetic stucco, often referred to as EIFS, consists of a polymer based laminate that is wet-applied, usually in two coats, to rigid insulation board that is fastened to the wall with adhesive, mechanical fasteners, or both. Polymer based (PB) systems, sometimes known as thin coat, soft coat, or flexible finishes, are the most common. The base coat for PB systems is usually only 1/16 in. thick and finish coat thickness is typically no thicker than the maximum sand particle size in the finish coat. While the PB skin repels water very effectively, problems arise when moisture gets behind the synthetic stucco and is trapped inside the wall. Trapped moisture eventually rots insulation, sheathing, and wood framing. It also corrodes metal framing and metal attachments. There have been fewer problems with EIFS used over solid bases such as concrete or masonry because these substrates are very stable and are not subject to rot or corrosion. Polymer modified mineral based (PM) exterior insulation and finish systems are sometimes known as thick coat, hard coat, or rigid finishes. The mineral base is Portland cement, while the polymer is usually an acrylic. PM systems have greater impact resistance than the PB systems, but are typically less than 1/3 the thickness of traditional three-coat stucco.