Excerpt from The Stucco Book, The Basics by Herb Nordmeyer
“Let’s get away from the chemistry for a little bit and look at a wall that is freshly plastered. IT tends to be a dark gray color. As time passes, some areas of the dark gray fade to a lighter gray. As more time passes more of the dark gray fades to a lighter gray. That dark gray color indicates that there is plenty of moisture present in the mud for chemical hydration to continue. That lighter gray color indicates that there is not enough moisture present for the chemical hydration to continue. That is a slight oversimplification, but pretty accurate.
If the wall dries out, it is difficult to get it wetted down again to re-create that dark gray stucco color. As a result, it is best to moisten the wall as often as necessary to prevent the dehydration. You are not trying to add water to the stucco, but rather to add as much water to the surface of the stucco as evaporates from the stucco.
The rate of hydration of the cement molecules is temperature-dependent. At lower temperatures, the rate slows and almost stops. If the wall freezes during the first 24 hours after applying the mud, the water in the wall turns to ice and expands. That is why ice floats on top of liquid water. When the water in the stucco freezes, it also expands and puts pressure on the stucco. This causes bonds to break and pieces of stucco to come loose. As a result, the stucco should not be allowed to freeze during that first critical 24 hours. After that first critical 24 hours, a portion of the water in the stucco has been chemically combined with the cement molecules. With that and with a minor loss of water from the stucco due to evaporation, there is some space within the stucco, so if the wall freezes, there is a possibility that no frost damage will occur. With each passing day, the wall can handle more freezing.
The first step in successfully curing stucco is to arrange your schedule so you do not have to apply stucco when freezing weather is anticipated or when strong drying conditions are likely to exist. f freezing weather is anticipated, plan the construction of the protection before you apply any stucco. After the stucco is applied, encloses it with protection and add gentle heat. A little heat over a long period of time is more effective than a lot of heat over a short period of time.
In hot weather, plan your day so you are never plastering in the sun. Come out early and start on the west walls so they will have a long curing period before the sun hits them. Then move to the southern walls. After the sun passes its zenith, move tot the eastern walls, and finally finish on the northern walls.
So, how should a wall be moistened? Use a Hudson-type garden sprayer. Wait until the wall is thumbprint hard, so water will not erode it, and then lightly moisten the entire wall. If you use a garden hose, you may erode some of the stucco. Spray the wall whenever the wall starts appearing just a little bit light.”
More details about curing stucco and a variety of other topics including application techniques, lath materials, the chemistry and history of stucco are available in The Stucco Book, The Basics by Herb Nordmeyer.
The University of Florida ASCE Gators won this year’s Concrete Canoe Competition. Each year Civil Engineer students from around the US, Canada and Mexico participate in regional and national competitions where they build a concrete canoe and race it. Some of the requirements of each team are to prove their concrete canoe will truly float before participating in the competition, complete a presentation about their process showing the various elements that make up their canoe and finally participate in male, female and co-ed races.
Nathan spraying the HERB-CRETE Stucco.
Nathan spraying his first wall.
Spray, Trowel, Spray, Trowel…
Local, organic heirloom tomatoes!
List of current brews on tap.
Back troweling the first coat of stucco to create greater adhesion with the second coat.
The mixing station- For the best mix be sure to use a tow-behind mortar mixer.
Here at ToolCrete we’re so lucky to get to work with some of the most interesting and amazing concrete projects going on around the world. Last fall we got a call from down under with an order for some sprayers to Steve Irwin’s Austraila Zoo in Queensland. They have a dedicated artist on staff who creates their custom sculptures found throughout the zoo. Cameron is that artist who combines many basic construction materials and molds them into these incredible works of art.
David Seils
Will Higginson is an architect/ builder who is in the final stage of completing his thinshell ferrocement performance stage. He built it for his yearly gatherings with friends and family where they spend a week celebrating the passing summer and many of his friends sing, dance and share their talents.
Lime putty is quick lime that has been hydrated and has a toothpaste consistency. It can be made directly from quick lime, or it can be made by adding water to hydrated lime. It has a place in historic restoration and a few other places, but it is not worth the effort for most mortar and stucco work.
High-cal lime is a hydrated lime that is produced for water purification, wastewater treatment, and many other industrial processes. There are people, including some who should know better, who use it for making mortars and stuccos, but the quality testing is such that sometimes it has oversized (problems can be caused by particles that are less than 1/8″ in diameter) particles that can lead to lime-pops months after a job is complete. The oversized particles are calcium oxide particles, and it takes them a while to hydrate. When they do, the resulting calcium hydroxide takes up more space, so a bit of the mortar is broken off. Usually this results in a conical hole in the plaster or mortar with a white dot in the center. An additional problem with high-cal lime is that it is more prone to causing lime burns than Type S dolomitic hydrated lime.
Type N hydrated lime is very similar to the high-cal lime, but there are more quality checks, and the oversized particles that cause lime-pops are not present. With Type N hydrated lime, over 8% of the lime can be unhydrated. The unhydrated portion may be fine particles that fairly easily hydrate, or it can be hard-burned particles that are very difficult to hydrate. Hard-burned particles usually have a glassy layer around them that takes a long time for the water to penetrate and bring about the hydration process. Since there is unhydrated calcium oxide in the Type N hydrated lime, it can cause lime burns on skin.
Type S hydrated lime has less than 8% unhydrated particles. Much of the Type S is produced from dolomitic limestone (calcium-magnesium carbonate). Since magnesium oxide is harder to hydrate than calcium oxide, the hydration usually is done in a pressure hydrator. As a result, virtually all of the calcium oxide is hydrated, and the magnesium oxide which is not hydrated is less likely to cause skin burns than calcium oxide. Type S hydrated lime particles are usually larger than the Type N hydrated lime particles and give the resulting mortar or stucco more body and more workability. Where it is available, the Type S dolomitic hydrated lime is well worth the extra money it costs.
David Kottman of Roanoke, Mo. is no fool. Like many savvy shoppers, he clocks a lot of research hours before making any purchase. It’s the smart thing to do. So when looking for a solution to resurface the block wall foundation of an old homestead building on property he had purchased, he spent lots of time on the Internet, several hours of which were on MortarSprayer.com.
