Estimating a grinding job sometimes feels like predicting the weather.

A lot of variables go into grinding concrete, making it difficult to judge length and cost. It's not uncommon for a customer to contact us in dismay when a job takes longer or is more expensive than they expected. These disappointments and delays, however, can be avoided with a better grasp on what goes into grinding.

First lay the groundwork by answering some questions:

What is the desired finish?

What is the current state of the concrete?

What kind of power do you have access to?

How are you disposing of the material you're grinding?

What is the size of the project?

How much time do you have?

First of all, what is your desired finish and what is the current state of the slab?

The smoother you need the surface, the more passes you will have to make. The current condition of the concrete determines both how many passes you need and what kind of tooling to use. A heavily damaged surface will inevitably need more passes and possibly more aggressive tooling. In order to remove coatings you will likely need to use PCD segments before grinding. With very thick coatings put the grinder away and start with a scraper.

Thinking about the end product is often the best place to start. What finish are you trying to achieve?

Next think about your power supply and how you plan to dispose of dust.

You may want to use a bigger, more powerful machine, but first ensure you have enough dedicated power to run it. The Husqvarna PG 820 RC, for example, is a 480 volt 3-phase machine. Without the on-site resources to power it you have two choices: use a smaller machine or rent a generator.

Grinding jobs inevitably create dust. You are, after all, removing a layer of the slab. For example, grinding a 50,000 square foot slab down one eighth of an inch will produce twenty cubic feet, or roughly 3,000 pounds of dust. We all understand that you need some kind of dust-collection system, but that doesn't entirely solve the problem. Vacuums can only hold so much and grinding will have to stop at regular intervals to change out bags. Furthermore, even a strong vacuum won't pick up everything, meaning leftover dust needs to be gathered some other way in between passes, most frequently with a foam squeegee. Take these stoppages into account when estimating how long a job will take and how much personnel you need.

Dust control is an essential but time-consuming part of grinding concrete.

Let's look at an example to get an idea of how some of those variables play out and look at the questions of time and slab size.

Using a Husqvarna PG 820 RC, a 32" grinder (mentioned above), it's common to grind 7,000 to 10,000 square feet per day. Some of the givens here are speedy dust disposal and tooling change-outs to keep the grinder running as consistently as possible. Grinding 10k a day requires a pretty smooth operation. Delays and/or extended down time easily push that number down to 5,000 square feet per day.

Larger slabs will cost you either in time (many days of grinding) or in added equipment and workforce. The truth is, you need to keep a grinder moving constantly to maximize output. Our on-site specialist Chris Hawkins has seen contractors achieve a staggering 19,000 square feet per day. The method? Two alternating grinders, with one grinder always at work while the other is prepared to jump back in. This brings us back to the question of time. If a speedy job is your priority, Chris' story shows that you can tear through a significant amount of concrete per day but at the added cost of more manpower and renting additional equipment.

Consider the size of the slab and the time you have available when choosing equipment.

If you can answer even half of the above questions when coming in to rent grinding equipment then you are twice as likely to get an accurate estimate.

We can help you choose the right equipment and tooling, but much of a project's schedule and spending comes down to the efficiency of the job site. Keep things moving, anticipate breaks and delays, and carefully delegate crew to avoid unpleasant surprises at the bottom line.