I am considering buying a 15years old home with hardcoat stucco siding. When looking at the stucco from a close distance I noticed a number of thin “hairline” cracks in it (they go in different directions, intersect etc.). The thickness of the cracks is not big – you couldn’t probably insert a coin into the crack. I wonder if this is a serious problem and if so how expensive it is to fix. Does the water get underneath the stucco through those cracks? Will they increase (in size and number) in time or they just will be “as is”? Thank you.
What do you mean by "hardcoat stucco siding"? (hardcoat vs. softcoat?) Do you just mean old fashioned three coat cement stucco as opposed to the new EFIS products? I will respond if you can answer these questions.
If what you are seeing are very thin cracks that occur mostly near returns or window and door openings, you are probably seeing typical curing/movement cracks which are normal with conventional stucco.
These will sometimes be numerous on stuccoed homes where the stucco contractor failed to install enough trim accessory joints to minimize cracking caused by normal expansion/contraction of the material. Trim Accessory Joints are what the trade calls various control joints, expansion joints, reveals or other devices or systems that divide the stucco membrane surface. The number and location of these are usually designated by an architect. Unfortunately, installation of a given number of trim accessory joints is still not a guaranty against movement and the cracking associated with it.
These are usually located strategically at wall penetrations, structural plate lines, existing joints in the building construction, cantilivers and where columns meet the walls and soffits. The maximum recommended length for wall panels with conventional stucco is 18ft, with the height to width ration not to exceed 3 to 1. Generally speaking, if you note too few accessory joints on the structure you can expect an abnormal amount of shrinkage/movement cracks. In most cases, these won't affect performance as long as they aren't ignored forever. Butyl or polyurethane caulks that match the color of the stucco as closely as possible can be used to seal these cracks. If you don't have a close match, make sure you use a paintable caulk and then get some touchup paint mixed up at a paint store so you can conceal the caulk.
Glenn is correct in pointing out that lawn sprinklers can cause problems with stucco, but this is generally only serious in locales where sprinklers are allowed to strike a building over extended periods of time and not allowed to dry out. As long as a proper underlayment has been used and weep screeds are properly installed, even wind-driven water won't cause severe problems, since stucco's ability to breath helps it remove any moisture left behind when rain forced through the surface via such cracks is conveyed to the outside via the screed. In 1996 the Northwest Wall and Ceiling Bureau sponsored extensive laboratory testing of stucco, by spraying three different 3/4 in. thick stucco formulations with 112 gallons of water per hour for two hours at a pressure equal to a 38mph wind. When the tests were concluded, no moisture or dampness was found on the back of the stucco membranes, resulting in an NWCB finding that a 3/4" thick coat of stucco, when properly mixed, applied and cured is water resistant. Add to that the underlayment, and stucco is a pretty good siding alternative.
Now, I want to point out that I'm talking about conventional 3-coat stucco - not the 1 coat type used in the southwest or E.I.F.S.(Exterior Insulation and Finishing System). These are different breeds of cat, and are best saved for another day's discussion.
By the way, where are you, anyway? There are a few regional differences in the way stucco is applied. It would help other participants to know before responding.
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