Cracking In Exterior Stucco

Having been in the construction industry for over thirty years and at Merlex for close to eighteen I am usually asked the same questions over and over. Through the years I have written letters explaining certain conditions and tend to use the same ones for similar circumstances. There are published reports and industry associations from which I have drawn much information and technical data.  I have sold lath and plaster, drywall, metal studs, masonry and related tools and aggregates that have given me much experience in the construction of walls and ceilings. I have consulted on structural issues, fire ratings, and water intrusion problems. I now feel uniquely suited to answer questions and offer solutions about frequently asked questions regarding stucco, plaster systems and the building envelope. I hope that I can have some lively discussions and learn a few things both locally and within other regions about stucco and related products and issues.

Topic #1   Cracking in exterior stucco

The single most discussed topic in Portland cement stucco is cracking. I have spent countless hours and many thousands of miles looking at cracks which don’t seem to change much over the years.

No one can guess how much the stucco will crack in your home, building etc. There are many reasons for cracking none having anything to do with the quality of material, level of workmanship or knowledge of the builder. It does have everything to do with how much the structure moves. All the variables for structural movement are in play including geological conditions, wind shear, movement and shrinkage of framing members, weight on the building envelope (walls) seismic activity and any other cause of stress to the building.  It is advisable to discuss this at length with your structural engineer, architect and general contractor before proceeding with the plaster and stucco. There are certainly some technological advances in the plaster system that can reduce (not eliminate) the incidence of structural cracking. The base and mesh system is the newest and most effective solution to significantly reduce the incidence of cracking. This is an additional coat of material consisting of a polymer modified base coat with an embedded fiberglass mesh for added reinforcement. The benefit is twofold: The first is the modification of the additional cement with polymer to allow for some movement or elasticity in the material. The second part of the system is the mesh that works as a slip joint to arrest cracks that emanate from some underlying stress. You can find more specific information on the Merlex site on the technical bulletin for Basex and the Basex frequently asked questions sheet.

I hope that I hear from industry experts, product reps, or other areas with some novel solutions to this old problem.