If too much water is introduced into the mix, the cement and sand cannot bond to each other and break apart. When the concrete starts to dry out, a crumbling zone occurs in which the particles do not stick together. Concrete looks like a stable and permanent material, but it is still porous and absorbs water. When this water trapped inside the concrete freezes, it pushes the cement binder outwards.
This expansion, and the resulting contraction when the water melts again, causes crumbling. If you live in an area with winter temperatures low enough for water to freeze, seal your concrete steps or walkways with a sealant once a year to keep water out. Concrete crumbling is usually caused by someone adding too much water to the mix. The water reacts with the cement to start the hardening process.
The label on the bag of cement usually indicates the amount of water to be added. Normally, the ratio will be two to one, two measures of dry mix to one measure of water. Measure the exact amount of water needed before adding it to the dry materials to avoid making the mix too wet. The most common cause of spalling is contractor error.
They either add extra water to the concrete as they finish it, or they start finishing the concrete before the spalling water leaves the surface of the concrete. Salt is slightly acidic and attacks the bonds that hold concrete together. In doing so, it enlarges the pores of the concrete, allowing more water to seep into the concrete. This effect is compounded by the fact that salt attracts and holds water, retaining fluids within the concrete.
When the temperature drops, and the water freezes and expands, the surface of the concrete splinters or flakes. After years of salting and freezing, the concrete begins to show real deterioration. He worked with Crane Engineering's corrosion resistance division on other concrete-related projects, and decided to contact his account manager, Keith Den Ruyter, to see what was needed to repair the concrete steps. A powerful pressure washer held close to the concrete surface and at a very low angle does a great job of lifting these weak areas of concrete.
In cold conditions, if the wet concrete is subject to freezing and thawing, the surface will dry flaky and cracked. When you find a damaged spot, clean it up and use a concrete filler, such as Fix-All, to patch the area. Too much, and you won't have a thick enough mix to shape stairs, pavements, or almost anything else where concrete is used. Concrete Resurfacer is made with Portland cement and a unique blend of polymers and additives that make it stronger and more durable.
Concrete is one of the most durable building materials available, but faulty installation, daily wear and tear, exposure to chemicals and even the hazards of extreme temperatures can take their toll on concrete surfaces. Use only the amount of water indicated in the mix instructions to prevent the concrete from being weak and crumbling under pressure. Expansion joints are placed in large expanses of concrete to prevent the surface from cracking as sections move imperceptibly over time as a result of temperature fluctuations or ground movement. Wearing a respiratory mask and goggles to keep airborne concrete dust at bay, the entire surface is sanded in several passes with a handheld grinder equipped with a series of diamond pads.
The key to success in applying this stucco is to ensure that the entire top layer of weak and compromised concrete has been removed. Concrete with a sufficient amount of Portland cement, properly mixed with not too much water, properly finished and cured, will withstand decades of frost. This inner core of concrete rarely crumbles, and the spalling defect is mainly an aesthetic issue.