Select Page


Adding water to ready mixed concrete is like breathing; it’s something that happens all the time almost without any thought. If we do invest any brain power, here are some thoughts that come to mind: What are the effects on the concrete properties? Are we complying with the job specifications or the building code? If we end up in front of a judge over this concrete, who is liable? That’s a lot more involved than inhale/exhale!

Before we jump in, let’s discuss the different names that are used. Sometimes, additional water added on the wash rack or on the job to adjust slump is often call temper water from the verb temper. Apparently, in the ready mixed industry, temper is also something that’s quite easy to lose! We also see the term retemper. That reminds me of the airlines who “preboard” and then “board.” Retemper implies water used to make an adjustment after the batcher and driver have added and adjusted their waters. Petrographers like to use that term retemper while evaluating paste under the microscope. Other names we know include: Mas Aqua, Free Super P, Flow Juice, etc. No matter what the name, ANY water added either intentionally or unintentionally to concrete and thoroughly mixed is always counted as mix water and becomes part of the water to cementitious ratio (w/cm). Exceeding the design w/cm ratio can lower strength, increase bleed water, increase shrinkage (cracking potential), and reduce the overall durability.

Our first stop on this knowledge quest is the law of the land – the building code. In Virginia, the statewide uniform building code incorporates ACI 318 as “the code”, so what does the building code (ACI 318) say about jobsite additions of water? The answer is nada… not a thing… silent. The building code does, however, specify maximum water to cementitious ratios (w/cm) for certain exposure classes of concrete. Therefore, we must conclude that jobsite additions will increase the w/cm and possibly exceed the maximum permitted by the code. The building code also gives you a procedure to calculate strength overdesign (safety factor) based on statistical criteria. The overdesign may be a restful safety blanket for added water, but lots of other variables are also competing for snippets of that blanket.

Next, we look at ASTM C94, Standard Specification for Ready Mixed Concrete. Many job specifications reference this document, and many of our delivery tickets do as well. If C94 is incorporated by reference in a project’s specification, or you write it on a COD ticket, then it becomes part of the contract. This is not like agreeing to terms for iTunes or Zillow. Section 9.3 says, “Mixing water shall consist of… water added at the job site in accordance with 12.7…” Section 12.7 basically says we can add water upon arrival at the jobsite “before discharge of concrete” to reach the required slump (flow) and mix for 30 revolutions. It also says water must be added under pressure and aimed for “proper distribution”. C94 says it is the manufacturer’s (producer’s) responsibility and requirement to determine the maximum amount of water that can be added to prevent exceeding the maximum designed w/cm ration for that mix. Finally, we are required to document the water added on the jobsite. Section 12.8 allows us to use automated monitoring equipment for enroute modifications to slump.

The last stop is the marbled steps of the courthouse. Hopefully we’ll never end up there. I’m not an attorney and would never give legal advice, but I have been called “Defendant” in the past, and here is what I learned. The judge does not know w/cm from a steaming pile. The judge does look at who has expressed duties and the presumption of expertise. A finisher who tells the judge they have 30 years of experience with “concrete” is telling the judge they have expertise. Harry the Homeowner does not, and therefore by default the producer does. Following C94 and documenting is always the key.

A great resource is the NRMCA’s Concrete In Practice #26. And of course, you should own the most updated version (2019) of ASTM C94-19.

Submitted by
Hank Keiper
The SEFA Group