We receive many calls about moisture intrusion, go figure.
After three hurricanes and buckets of rain, many of us in central Florida may have personal experience with moisture intrusion through the walls of our homes and aren't lookin' to repeat. With Charley, we had a quick storm blow through and not a lot of rain. With Frances, we had a lot of rain but not a lot of wind. With Jeanne, we got it all. Hard driving winds and rain that was relentless for hours.
So how does water get in? Answer, physics. 1. Gravity is pretty reliable, up to down. 2. Greater pressure to lower pressure. 3. Temperature, warmer to cooler. Well yeah, who doesn't want to be cooler man?! 4. More to less, higher concentration to lower concentration, more relaxing. Now there is always the human factor (poor construction) but there's not much you and I can do with regards to time travel, so….
Let's look at a typical block wall. There are some interesting dynamics here. Different materials all put together that breath, that shrink, that move…hello cracks. Now ask this system to perform like a submarine and you get just as silly an answer…hello moisture intrusion. Let's get to the bottom of this. OK, foundation settlement can cause cracks however this source is not the most prevalent and not the focus of this article. Most cracks in block walls come from the materials and application of these materials in the wall.
A recent UCF Constructability Lab study focused on block wall performance with regards to moisture intrusion right here in central Florida! I read through all 77 pages of the UCF study and can paraphrase the points most applicable to us…block leaks like a sieve…stucco provides the majority of the “water proofing”…paint just helps. If building codes and ASTM Standards were followed to a T, we could reduce settling and moisture intrusion issues almost entirely. What are the chances of that occurring every time? Can you say “Beer:30” (hiccup)? Hey, we're human right. Follow the money honey! Git-er-done!
Most of our homes have a stucco type veneer whether it's on wood frame or concrete block. Stucco is made up largely of Portland cement and is porous by nature. When stucco is applied it “cures”. As part of the curing process, stucco gives up moisture to the atmosphere. As it dries, it cracks kinda like our skin. There is an ASTM C926 Standard that requires multiple applications, thicknesses and curing times, but according to the UCF study, proper application is rare.
A minimum thickness of 4/8-7/8" is required for block and frame construction respectively per FBCR703.11. Instead, an average of 3/8-5/8" is what is commonly found in the field. Secondly, if stucco were
installed in a 2 or 3 coat process with proper curing time in between, we simply would not have the moisture intrusion issues we currently encounter. The physics thing takes over from here…gravity, pressure and temperature gradients, capillary action, yada yada yada.
So here we have a porous material with cracks subjected to wind driven rain, what'll ya think will happen? Picture a napkin dipped in water. The water races right up the napkin via capillary action. Common sense (and physics mentioned above) says the more paths provided and the longer those paths are exposed to inclement weather, the more vulnerable a wall system (or anything else) is to moisture intrusion and subsequent adverse ramifications…Duh. Now during our normal 15 minute Florida thunderstorms, we just don't have the quantity of rain and Jeanne type winds and thus we just don't experience the moisture intrusion problems we had with the hurricanes. However the UCF study found that cracks don't need to be wide to allow moisture penetration. Cracks .39mm or 1/64” allowed moisture penetration and accumulation at the base of test walls.
Besides the stucco shrinkage and cracking, Forcon International Corp 1992 TEK 10-1A 2001, Gulde 2006 determined another common cause of shrinkage cracks in masonry walls comes from using "wet" or uncured concrete block. When uncured blocks are used to construct a masonry wall, they continue to cure and experience a significant amount of shrinkage. Typical shrinkage in a 50 foot masonry wall range from 3.1 to 6.9 mm. The older the masonry is, the moisture loss decreases as compared with the loss in the beginning of it's life but I read a stat somewhere that concrete will continue to shrink over it's entire lifetime while a brick will continue to expand over it's lifetime. Interesting huh?
