Best Practices for a Residential Concrete Pour: Part 2
"In Part 1 of this series, Francis covered site prep and form work, required tools and materials, and a few tips to make your work easier and more productive. In this article, Francis discusses what to consider before placing your concrete order."
In this series on concrete basics, we’re collaborating with Francis Rzegocki from Excel General Contractor. Prior to joining Excel, Francis had extensive experience working in the concrete industry with both heavy civil and residential projects. In addition to his construction industry experience, Francis holds a degree in mechanical engineering from Worcester Polytechnic Institute in Worcester, Mass.
In speaking with Francis, he shared with me that prior to entering the concrete construction trades, he was actually nervous and uncomfortable with the idea of taking on a concrete pour. He decided to embrace that fear and go learn everything he could about the craft, turning it into a strength for him when he returned to the remodeling business.
In Part 1 of this series, Francis covered site prep and form work, as well as the required tools, materials and a few tips to make your work easier and more productive. In this article, Francis will be discussing all the different decisions that need to be considered when placing your concrete order. Take it away, Francis.
Figuring quantity and mix components
Although there's probably an app for calculating your concrete needs, you can fall back on your basic math background to accomplish your goal. Width times length times depth will give you the cubic feet needed for the project. Dividing that figure by 27 will give you the number of cubic yards. You'll want to order enough material so you don’t run short.
Once you have your order quantity figured out there are a few other components in the mix you need to decide on. One of those is aggregate size. For most residential concrete projects, you'll be okay choosing pea-gravel-sized aggregate, unless an engineer specifies something larger. Larger aggregate can really impact you in the finishing stage of the project, especially if your mix starts to cure sooner than expected.
The other decision is how much cement you want used in your concrete mix. For most projects, a “six sack” mix (six bags per cubic yard) will suffice. Again, these details can be dictated by engineering specs, so make sure you check with all the stakeholders on the project. The dispatcher may ask you the PSI level you're trying to achieve. If you provide that info, they'll mix your batch to achieve that requirement.
Wet/dry consistency
As long as you're placing orders for concrete, you'll be balancing two competing needs: work-ability versus maintaining the integrity (strength) of the mix. As you watch the first bit of concrete roll out of the drum and fall into the chute, you don’t want it to be breaking apart in clumps. That would be a sign that the consistency is pretty dry and will make all the work ahead of you that much more difficult. Going too far the other way can also diminish the integrity of your mix. If the project has strict engineering requirements for the concrete, this could potentially lead to expensive repair remedies.
Weather and choosing a delivery date
Unless your pour is indoors, you must factor in the weather when deciding on a delivery date. Try to look at three separate weather forecasts to inform your decision. A good rule of thumb is to not schedule a concrete pour if the chance of rain is greater than 20 percent.
Other weather factors can affect your concrete pour, too. Things like temperature, humidity, wind, direct sunlight, and shade all play a role in the pace at which your concrete will set up and cure. In cooler weather, some tradespersons choose to add calcium and/or hot water to their mix in an effort to help it set up more quickly. This can be a huge help if all the stars line up for you. It can also be a recipe for disaster if other weather conditions start working against you or you don’t have enough skilled labor to keep up.
To pump or not to pump
The decision whether or not to order a pump truck to support your project is typically dictated by access. The maximum distance to place concrete directly out of the truck chute is about 15 feet from the back of the truck. For anything further than that, you can choose to wheelbarrow product the rest of the way or look at options for ordering a pump truck.
If you decide on a pump truck, add another yard of concrete to your original estimate. Lots of concrete is used in just filling up the hose, and it doesn’t necessarily make it into your forms.
Communication of site conditions
Some of the most important things to share with the dispatcher are the details pertaining to conditions on your pour site. You'll want to convey all the key safety concerns, like overhead power lines and open trenches. It's also wise to talk over any potential property damage concerns — items such as driveways, landscaping, fences, and masonry work.
We want to thank Francis again for sharing, and we hope this information helped increase your knowledge and confidence for the next time you choose to tackle a concrete project. Stay tuned for Part 3 of this series, in which Francis talks best practices for the day of the pour. And for even more on concrete, check out this post on cement board screws, this blog on Rapid Set Cement All, and this guide on how to use set control and flow control.
