MMI DOOR Interior Doors are an intricate part of home design and upgrading the doors in your home can significantly increase your home's value. Our primed shaker flat panel doors are manufactured to eliminate warp, panel shifting and rattling so your shaker door performs properly for years to come. Using a superior priming process, four coats of primer are applied to each door slab with sanding between coats. This means that finishing your MMI DOOR primed shaker flat panel door is a snap.