Several weeks ago, I had the pleasure of spending my evening with a construction crew taking concrete samples from an existing floor slab. For older structures, the concrete strength is listed on a drawing that took a vacation and never came back, so in order to verify the strength, you have to take a core sample and send it to the lab. This is how its done.

Step 1. Make sure you aren't drilling through existing reinforcement bars

We will be drilling through the concrete slab, so it's important that we do our very best to not drill through a piece of reinforcing steel. In most cases, removing 1 bar will do nothing to your structural system, but you should strive to not touch them if you can help it. Since we are professionals, we have a special tool called a pacometer, which is nothing more than a fancy magnet that we drag across the floor.

Step 2. Core through the slab to collect the sample

Once you know the best location to drill, you position the core drilling machine, which is nothing more than a drill press on wheels, and you core away. Water is typically used to keep dust down, lubricate the core bit and keep the bit cool. These bits only last about 10 cores before they go bad.

In most cases, you'll end up coring THROUGH the whole slab. Obviously there is a hazard with simply coring through someone else's ceiling. Safety is always a concern for these types of work, so if you can get away with not coring through the slab, then certainly dont!

Step 3: Retrieve the sample

This part is a bit tricky. If you can retrieve the sample without coring through, then you can snap the core off with a little bit of force and you are set. But if you need to core through slab, then be prepared to catch it from below. Most commonly a bucket with water and a radio is all that is necessary. In this photo, we opted for the break it off method.

Step 4.

Send it off to the lab! I'll post up with the results in my next post and talk about how we read and analyze them! Stay tuned