I am an architect whose client wants to renovate a strip shopping center for office use. The back wall is cmu with a new coat of paint. If you tap on the wall, you can tell the paint has not bonded to the cmu. The roof and parapets need to be replaced. What needs to be considered before applying a new surface to the exterior face of cmu that is still moist?
No paint, coating, or primer should be installed on the surface of CMU that is visibly damp. If there is moisture in the block, this moisture may try to evaporate through the coating, causing bubbles and delaminations, or it may lead to efflorescence behind the coating, resulting in failure of the coating and/or damage to the block surface. If possible, protect the block surface from rain and allow it to dry fully prior to recoating. The poorly bonded paint should be removed as completely as possible prior to recoating. If possible, avoid paint removal using high-pressure water spray. This will drive more moisture into the wall, and potentially create more problems than it solves. Often mechanical removal with a grinder or sandblast is the best way to remove a coating on block, but care should be taken to repoint any joints damaged by the paint removal process. When a coating is installed, it is best to use an elastomeric coating instead of normal exterior paints. Elastomeric coatings are more breathable than typical paint, and they are flexible enough to bridge small cracks. A block fill primer may be required (especially if the block is split face) in order to get even coverage of the coating without numerous holidays (pin holes). If you are considering overcladding the CMU with stucco or a veneer, the treatment of the block surface becomes less critical. Use a membrane weather barrier such as Tyvek Commercial Wrap instead of a fluid applied membrane, and the existing failed paint is no longer critical. It would still be advisable to scrape off loose paint to allow the block surface to breathe more freely. Since Tyvek is very breathable, installing this material over a wall with some internal moisture is not as objectionable, but it would still be best to avoid installation over a visibly damp wall.
I am an architect whose client wants to renovate a strip shopping center for office use. The back wall is cmu with a new coat of paint. If you tap on the wall, you can tell the paint has not bonded to the cmu. The roof and parapets need to be replaced. What needs to be considered before applying a new surface to the exterior face of cmu that is still moist?
No paint, coating, or primer should be installed on the surface of CMU that is visibly damp. If there is moisture in the block, this moisture may try to evaporate through the coating, causing bubbles and delaminations, or it may lead to efflorescence behind the coating, resulting in failure of the coating and/or damage to the block surface. If possible, protect the block surface from rain and allow it to dry fully prior to recoating. The poorly bonded paint should be removed as completely as possible prior to recoating. If possible, avoid paint removal using high-pressure water spray. This will drive more moisture into the wall, and potentially create more problems than it solves. Often mechanical removal with a grinder or sandblast is the best way to remove a coating on block, but care should be taken to repoint any joints damaged by the paint removal process. When a coating is installed, it is best to use an elastomeric coating instead of normal exterior paints. Elastomeric coatings are more breathable than typical paint, and they are flexible enough to bridge small cracks. A block fill primer may be required (especially if the block is split face) in order to get even coverage of the coating without numerous holidays (pin holes). If you are considering overcladding the CMU with stucco or a veneer, the treatment of the block surface becomes less critical. Use a membrane weather barrier such as Tyvek Commercial Wrap instead of a fluid applied membrane, and the existing failed paint is no longer critical. It would still be advisable to scrape off loose paint to allow the block surface to breathe more freely. Since Tyvek is very breathable, installing this material over a wall with some internal moisture is not as objectionable, but it would still be best to avoid installation over a visibly damp wall.