When faced with a softer concrete, you may be at a loss for what you can do to improve its appearance. Can it withstand grinding and polishing, or will it just look worse? It’s our experience that every concrete slab can be polished to a mirror-like shine, if that’s the look you’re after. Polishing soft concrete can be done, it’s just more time consuming and can require a larger budget. However, if you have the resources, we’re going to walk you through how you can polish soft concrete.

What Is Soft Concrete?

Concrete slabs are a mixture of cement, sand, aggregates like gravel or rock, and water. As the liquid sets, crystalline bonds form holding the aggregates together. Great care must be taken when combining materials to ensure proper ratios, otherwise the concrete will be a poorer quality.

You get a soft concrete when the crystalline structure within the slab is widely dispersed. The bonds aren’t as strong and there’s a higher porosity. Often this is caused by adding too much water to the cement and aggregate and air pockets getting trapped within the slab during the cure.

Preparing to Polish a Soft Concrete Slab

Trying to grind and polish soft concrete, it’s important to understand that aggregate exposure can’t be controlled. The slab must be ground to the point of exposing a stronger concrete, which is problematic in and of itself. There may be color differences, large clumps of aggregate throughout the slab, and micropitting are all apparent. Air holes can also be common after grinding down past the first 1/32″.

Using a Concrete Densifier

One thing that you absolutely have to do when working with soft concrete is apply a concrete densifier. Yes, the bond of diamond tools plays a role in how long it the tool itself will last (more on that in a moment), but it does nothing regarding making the concrete structure stronger or improving the cut.

With a little help from some chemical reactions caused by densifying concrete, you can easily get a more dense, durable floor with a tighter crystalline structure that makes it grinding and polishing more effective and more efficient. Most likely, you’ll need to densify the concrete twice.

Diamond Tooling

Any grind you do before applying densifier needs to be able to hold up to the highly abrasive texture of soft concrete. Generally, a hard bond tool is needed to hold up for any length of time, but after the densifier is used, you can switch to a softer bond.

Grind and Polish a Prepared Slab

Before you begin the full process, prior to densification, you’ll want to perform a mock-up and grind the floor with a tool that can take off the top layer of concrete. You’ll want to achieve a uniform exposure without cutting uncontrollably. A hard bonded diamond with the pocket weights added to your floor grinder should get the job done well. As you’re doing this, make sure you’re getting a consistent, even scratch pattern without variation or low spots. Clean the area thoroughly and apply densifier at 1.5 times the manufacturer’s recommended amount.

Polishing Soft Concrete the Right Way

After the first coat of densifier, you can begin polishing the floor using your first metal polishing tool. If you’re using a set of concrete tooling, such as the CLC Diamond System from STI, you’ll start with CLC #1. You’ll keep on moving through the steps, and after your first resin pad, you’ll want to apply another coat of densifier before moving forward with the polishing process, finishing with the final grit that will help you achieve your preferred finish.

Contact Us for Concrete Grinding Equipment

This is just skimming the surface of what it means to polish soft concrete. We always recommend reaching out to manufacturers to learn more about how their products will work on the substrate you’re working with. No matter what kind of equipment you need, we carry the diamond tooling, chemicals, and even heavy duty floor grinders you need to get the job done right. Reach out today to speak with a member of our sales team by calling   (815) 472-9744 or by filling out our contact form to get started!