Although it may feel and look the same, not knowing the difference in concrete mixes could lead to foundation failures after your builder is long gone.  Many times folks will think if the concrete is hard, all is well.  Sorry, not the true, often foundations and driveways fail because the mix did not gain the strength it needed to perform as intended.  The strength of a concrete pour is effected by numerous factors, however, today we will focus on the actual concrete mix that is ordered by the builder.

Most foundation designs require a mix that tests out at 3,000 psi (pounds per square inch), which is a means of measuring the strength of mix when cured after 28 days.  The most common mix that is ordered to accomplish this is a fly ash mix which substitutes a recycled mix (fly ash) for a part of the cement mix.  When prepared properly this mix can achieve a 3,000 psi strength, however, there is little room for error. 

Many of the green building programs suggest using the greatest fly ash concentration possible in the concrete mix.  It may be earth friendly (jury is still) but how much more in resources and material will be needed to fix the failures due to the concrete not performing at the strength level needed.  Being “green” is not always the best answer.  I will blog more on how “green” is not always responsible in building and no amount of government mandates or PR can change the laws of physics and economics.  Sorry, I digress, back to the hard cool stuff, concrete.

One way to determine if your builder is serious about foundation strength is to ask what type of mix he uses for his concrete.  If he doesn’t know, I would be concerned.  Many of the top tier builders use a true 5 sack mix, which means that there are 5 sacks of mix in every yard of cement.  The more mix the stronger the concrete, in some cases we use 6 sacks or more.  (Trivia – the more Portland mix in the concrete the hotter the concrete pours).

The 5 sack mix is designed to test out at 3,500 psi or greater (some test out at over 4,000 psi).  This additional strength helps your foundation meet the unforseen pressures on your foundation.  We refer to this as a margin of safety. 

You may ask why if this mix is stronger would anyone ever use another mix.  There are several reasons a builder may not use the stronger/better mix;

1 – Many builders just don’t know building science.  If you discussed concrete mixes or psi, their eyes would glaze over and they would start to day dream about tee times.  They came into the home-building industry as a means of getting rich (excuse me as I laugh, I am sure they have now discovered, that ain’t going to happen, OK I am back).  You could walk these guys through a house and they couldn’t tell you how a foundation works, much less know how to estimate material or how a wall should be braced.  If you really want to perplex them, ask them some code questions on electrical or plumbing.  If you want a professional builder to oversee your home, this guy would NOT be your guy.

 2 – They turn their foundations over to subcontractors on a turn-key basis and trust them to do what they need to do to get the foundation poured.  The builder may not show back up to the job site until after the foundation is poured.  That is not to say they don’t care but only they are not as concerned about these types of specifications of your home.  If you want a control freak to oversee your new home construction, this builder would NOT be your guy.

3 – They just want to save money and if the fly ash will save them a few hundred dollars that is what they will order.  If something happens they will worry about it later or hope the warranty company covers it.  If you want someone who is willing to invest in the right materials and workers to build your home, this guy would NOT be your guy.

Other factors that can affect concrete strength includes the weather, how much water is in the mix, how long of time between each truck pours, quality of the concrete, how long the concrete has been in the truck, how the cables are positioned in the foundation, obstructions in the beams, mud on the rebar/cables, quality of the labor, weather, etc..  You just cannot back up a truck and pour concrete wait for it to get hard.  The difference between the top tier builders and the “discount Joes” begins at how they pour their foundations.  More on that to come.

There are thousands of ways for builders to take short cuts on building your home that you will NEVER be able to detect or understand.  The guys (and gals) who take the short cuts are often the least expensive builders.  Over my nearly 2 decades in this industry, I have seen countless families go for the lowest price only to regret the decision.  A well built home starts with the foundation, if your builder is willing to use the “good stuff” you are off to a good start.  If he is not, then………

Please feel free to leave your comments (once I figure out how to do that), drop us an email at mike@garabedianproperties.com or call our office at 817-748-2669.  I also encourage you to visit www.garabedianproperties.com to see our entire website.