Stucco (Portland cement plaster) is often removed from a building to assess if proper flashing has been installed, fix leaky windows, repair wood framing members damaged by water or other causes that would cause the stucco around windows to be removed. Patching and replacing the stucco membrane is necessary. Depending on the substrate, framing and overall remediation plans, removal procedures can differ. The process outlined below is for the removal and replacement of cement stucco on wood framed walls around windows. This guide is limited to stucco removal and replacement and is not applicable to the installation of windows and associated flashings. There are many window forms and styles and a number of flashing techniques. This paper is intended to concentrate on the remediation work of lath and cement plaster. Learn more by visiting Depend Exteriors-Stucco Replacement.
Determining the building owner’s expectations and informing them of the finishing options is significant. Depending on the degree or preference of finish appearance, the finishing choices for repairs around windows and should be addressed before the start of work. For all parties involved, the following will assist with some decisions, choices and help clear up uncertainty.
Before making any decisions on the final scope of repairs, a thorough assessment of the exterior plaster should be carried out by competent people. The type of finish coat (acrylic or cement) on the building and the overall condition of the walls are a significant item required to assess the full extent of stucco repairs. Has the structure been painted and what kind of paint has been used? Buildings with elastomeric paint styles can limit repair choices.
Removing stucco can be very dusty; it is always advised to use protective clothing, eye protection, and a respirator. Using a masonry blade, the stucco removal is best achieved by removing the stucco with a power saw. The blade, normally 3/4 of an inch, should be set to just shy of the stucco membrane’s maximum thickness. This will guard against harm to the underlying weather-resistive (WR) membrane. Masonry blades wear down easily and the blade depth may need to be regularly changed. The cuts in the stucco should be around 12 to 24 inches from the window frame. As they should hit the next framing member, vertical cuts can be further away from the window (stud). A cold chisel may be inserted into the saw cut once the saw cuts are complete and used to crack or fracture the last remaining uncut plaster thickness. With minimal disruption to the underlying WR membrane, the stucco can then be taken off the wall. It is recommended to cut the stucco into squares for large areas of removal, which can be easily done.
The WR membrane can be affixed to the back of the stucco in some unusual cases. It would be necessary in these cases to remove the stucco back to the point where the WR membrane is not bonded to the stucco.
It is recommended that the cut stucco edge be straight and smooth and that the edges be jagged and rough. This will build a stronger key (bond) between the current stucco and the new patch and will minimise the risk of a separation break. In order to chip away small bits, a hammer may be used, leaving some of the metal lath exposed if necessary.
To minimise tears, holes or other harm to the WR membrane, the WR membrane should be peeled back carefully. For proper lap and integration with flashings, some current WR membrane should be left. When final lathing takes place, a minimum two-inch over lap on horizontal joints and a six-inch overlap on vertical joints of the WR membrane will be needed.