A question for concrete guys

[Jaguar Fan]

I have a question (most likely a dumb question) for concrete guys.

When you pour a slab for a warehouse or big-box store with shelving that goes up quite high, it seems to me the concrete slab has very tight tolerance & is extremely level -- that is, a shelf (maybe 20 feet or more above ground) is extremely level.

In contrast, a slab for a residence doesn't seem to be nearly so level.

Are there different specs for what constitutes "level" for industrial applications versus residences? How do you get concrete that level?

 

[chrislehr]

In for this answer. I have been making way more shims then I want to be making to keep things level out there.

 

[boiler7904]

The short answer is that on a residential project, the crew is going to be working in the traditional way that everyone is used to seeing. Today's labor force doesn't have the motivation or sense of pride in work to get good results which used to be considered your basic level of craftsmanship. Work ethic and [lack of] training are leading us toward lower and lower quality construction.

On industrial and commercial jobs, the industry has been moving towards a "super-flat" specification for years which sets tolerances for flatness and level which can vary from project to project depending on intended final use and traffic patterns. To add to that, you can have flat without being level as in the case of a ramp.

Super Flat Floors

To get a superflat floor, a laser screed similar to this is typically used:

Somero Laser Screed

Because of cost and machine size / access to the building, it isn't going to work every job but it's an interesting piece of equipment to see when you have the right applciation. The only job which I've had one on in 5 years was a high school gymnasium that was getting a wood athletic floor system over the top of the concrete slab. Access to that job was so much of a problem that we had to leave a 12'x16' hole in one wall of the gym for the machine and concrete trucks to get through.

 

[brownbagg]

commerical slab are done with what called "Superflats" that is 1/8 inch different in 100 feet both ways. They required a lazer screed machine and very low slumps. They have to be superflat due to forklift low at high elevation, its not fun hitting a ridge with a load twenty feet up. They people that do superflat slab earn every penny, there are some strict requirement. If its not flat is gets torn out on contractor nickel. and redone.

 

[ckeggs]

Here is a link to a very good explanation of the "F" number which places a numerical value on both the flatness (variation from highest to lowest point over a given range) and levelness (slope over a given range). As stated earlier as the requirement for flat floor increases so does the labor and cost involved to achieve the desired result.

http://www.pdhonline.org/courses/s130/s130.htm

 

[Jaguar Fan]

Thanks guys!