Flaking or Chipping Concrete, Causes and Solutions

Question: What does your concrete driveway and a birthday cake have in common?

Answer: Chemistry and proportions.

When baking a cake if you add too much water, oil or flour your cake isn’t going to turn out well.  It may come out of the oven looking unscathed but once you cut into it or try to frost it the mistakes are obvious.  The same is true for concrete, in order to achieve a long-lasting finished product the ratios of “ingredients” must be carefully observed.

Basic concrete from the plant is designed at a 5 “slump”; the lower the slump, the less water and stronger product, the higher the slump, the more water and weaker product.  “Slump” refers to the wetness of the concrete.

Higher slump concrete is easier for the contractor to work, lower slump concrete is thicker and requires more effort to spread, screed, trowel and finish.  Similar to your birthday cake’s batter, a lot of water will make it easy to mix, less water is going to require  more effort from you and your spatula.

In Idaho, where the temperature ranges from below zero to above 100, concrete consistency is especially important.  By pouring at around a 5 slump we work with Idaho’s varying climate rather than against it.

The basic science of concrete is this: When concrete is poured the heavier aggregate that is part of a basic flat work mixture falls to the bottom through power screeding, and the creamy cement rises to the top, if additional water is added to the layer of cream the consistency is changed and while it may look fine in the short term, it is not a viable option for the long life of your concrete, and if your concrete can’t last forever, what can?

If your concrete flat work is chipping or flaking off on top, there are 3 reasons that are likely the cause:

1.  Too much water added to the concrete mix, aka, higher slump.  Contractors will order and pour this mixture for several reasons, it is easier to work with and to get a nice, smooth finish.  Unfortunately, that smooth finish is more apt to chip and flake off over the entire surface because the integrity of the creamy top cement has been sacrificed with the extra water.  This creamy top is more porous absorbs water easily, when that water then freezes and expands it causes this layer to separate or “pop” from the lower layers.

2.  Water thrown on concrete slab after it has started to set up, during the steel troweling process can help to get a finish on a slab that is setting up too quickly.  While this may work for the (very) short term, it is not a sustainable option for the long life of your concrete.  Water placed on a wet concrete slab will lead to random chipping, where water was weakened the cream.  This is also part of the reason we will not schedule concrete flat work pours on days that have more than a 15% chance of rain, an ill timed rain shower can ruin a whole slab without you even knowing it.

3.  Frozen concrete.  Like a cake baked at the wrong temperature it will most likely it will chip, crack and flake immediately.

You may be told your flaking driveway is a result of the rock-salt or ice melt used on your concrete.  While the use of ice melt may encourage the cement to flake faster, it is not the root cause.  You can see the difference between your city installed sidewalk and driveway; chances are the city sidewalk is unscathed by the use of ice melt, this is because the sidewalks are poured at a much lower slump usually a 2 or 3, the top layer of cement is thick and hard on these sidewalks, as your driveway and other flat work should also be if poured correctly.  You may also notice that the city sidewalks do not have the nice finish that your residential flat work does, the higher slump does not lend itself to the smooth finish desired in residential applications, the 5 slump of residential concrete is a happy medium for strength and appearances.

Unfortunately too much water in concrete can be a costly mistake.  Some contractors specialize in “resurfacing” concrete (grinding off the chipping layer and re pouring a top coat).  However,  just like that cake you baked with too much water, when it comes time to frost it the frosting won’t stick to a crumbling cake.  A top layer of concrete will most likely peel and crack because of the inferior product it is being poured on top of as well as Idaho’s weather conditions.  Also, verify that product they are selling is warrantied for outdoor use or vehicle use (if applicable) and that ice melt won’t harm the overlay.  The only proven long-term solution is to tear out the failing flat work and replace it with the correct mixture, poured the correct way.

When selecting a concrete contractor, do your homework.  Request that they do not use any mixture above a 5 slump.  These simple things can keep your concrete investment looking good for a lifetime.  Contact Redco Concrete Solutions for more information and a free estimate in the Boise area.