Plaster and stucco are porous materials and therefore susceptible to staining. Stains come from anything that can leach into the plaster through moisture and water. The most common being the planters and dirt that we pile up against the bottom of our homes. Code dictates the bottom of the plaster (the termination screed) should be 4 inches above softscape (planter’s, dirt, the ground, etc.) and 2 inches above hardscape (brick paving, concrete, etc.). Moisture carries the dirt and organic material into the stucco. That is why you can’t clean the stucco; the staining is not on the surface it is in the material. Another common place for staining to occur is from decks and roofs particularly where there is no overhang or gutters to divert water from washing down onto the face of the stucco. The water again carries the dirt and is absorbed into the plaster. There are ways to prevent this: as mentioned, try to divert water away from the plaster walls. If there are planters right up against the house you can pull back the dirt and treat the bottom of the structure with a waterproofing product like Super Blockade. This is a cementitious product that lasts many years and prevents absorption of moisture. You can also seal the stucco with a good penetrating sealer like MicroSeal II. This chemical prevents moisture from going into the wall but still allows the wall to breath. Keep in mind, these long lasting sealers penetrate and will only protect the surface if they are built up to impregnate the pours all the way to the surface. The primary function of a penetrating sealer is to keep water out of the wall cavity. Most damage is done if water is allowed into the wall. Surface moisture is typically an aesthetic problem. Of course, over time, water will degrade the surface through efflorescence and delimitation. Since the problem is already present we should discuss how to solve it. Paint is not the answer as paint disrupts the vapor from leaving the wall and has to be re-applied regularly. Fog coat is the product that is supposed to be used for stucco. It is cement paint and can be spray applied to make the wall look new again. Following this process a sealer should be applied to keep the problem from re-occurring.
|Microseal II application - Dublin City Hall Dublin, CA|