Repairing Hairline Cracks In Exterior Stucco. DIY Repairs Many homes that have stucco as an exterior coating have cracking issues, but most of. Cracks disfigure the look of your Exterior Stucco Surface. This step by step guide can help show you how to repair cracks on Stucco surfaces.

Cracks appear in stucco walls of buildings because the ground actually moves, and the building actually moves, and with time and the wet/dry/wet/dry annual seasonal patterns, the ground swells-and-shrinks and the building settles somewhat unpredictably over the decades. The stucco walls don’t stretch, not worth-a-hoot. When the building moves, then one part of the foundation goes a bit up, down or sideways relative to another part, and then the stucco cracks. Stucco is basically cement.

When painted, it is very weather-resistant and does not have the rot-issues of wood; that’s why it is used on so many buildings. Repairing a crack in stucco is often done with various caulks or cement, and usually the crack opens up again. There are two reasons: The cement patch can’t stretch, and the caulk did not stick. These have underlying them one common denominator: the building is still moving. Patching the crack did nothing to stabilize the foundation, or change the seasonal swelling-and-shrinkage of the ground. The crack is going to continue to open-and-close, and usually widens, on-the-average, as time goes.

Furthermore, the crack movement usually exceeds the elastic limits of whatever-was-used to fill the crack, even if it was not cement. Here’s why: Let’s say that we have a reasonably stable building, and the settling factor happened over many years. However, the ground swelling-and-shrinkage happens seasonally. So, eventually a crack starts, and over many years it slowly widens.

Enable Jit Debugging Windows Vista here. But, from winter-to-summer-to-winter-to-summer, it is also opening-and-closing-and-opening-and-closing, due to the seasonal ground movement. So, the crack might be 1/16” one year, and 1/8” five years later.

But, from winter-to-summer-to-winter-to-summer, it might open-and-close by 1/16” more-or-less. Early in the cycle we have a crack that goes from zero to 1/8”. Later in the cycle it might go from 1/16” to 3/16”, and then 1/8”-to-1/4”, and so-on. There just is not anything that will stretch that much and still stay stuck to the stucco, which has not got great tensile strength anyway. If you even used an epoxy glue in the crack, it would just pull off some stucco when the building asked the crack to open-up more. This is a Mechanical problem, and it needs a Mechanical solution. The simplest and least expensive one I know of is to vee-groove the crack, so it is much wider at the surface, such as a half-inch for a 1/16” crack.

Now, when that crack opens-and-closes by 1/16” more-or-less, the surface stretches-or-shrinks by a sixteenth out of ½, which is one out-of-eight, and that’s a very mild elongation; one that even a low-quality (inexpensive) latex-acrylic caulk can tolerate. However, if you want a really long-lasting repair, I’d recommend something that does not shrink when curing and sticks by real chemical bonding, and that’s a sealant called 5200, made by 3M. The idea is not to fill the entire crack or even the entire vee with the caulk, but to fill the upper part of the vee at least. A piece of twine or soft rope can be pressed into the bottom of the vee, so the sealant does not go into the crack itself. Actually, you don’t want it in the crack itself; if it did, then when the building tried to push that crack closed, it would just act as a wedge and another crack in the stucco would eventually open up somewhere else.

Incidentally, that’s another reason why filling cracks with cement does not work in the long term. Stucco is similar to wood in that it does not have a strongly attached surface; old stucco is often somewhat crumbly, due at least in part to its having been made with a lot of air mixed in with the cement-and-sand-and-gravel.

Some stucco is even sprayed, and that can easily be aerated. Whipping-in air minimizes shrinkage-and-cracking while curing, and also air costs less than stucco. What this means is that we need some kind of primer to glue and strengthen the stucco surface, and also something to chemically bond to whatever-kind-of-caulk you are going to use. Smith & Company makes a really good one, and it’s called Permanent Stucco Primer. That’s enough Theory. Now, let’s talk about Products, and getting the job done.

The cement surface must be reasonably dry before continuing. Moving air is the most efficient means of evaporating water.