What Type of Mixer Should I Buy?

Question:
I want to buy a portable mixer for making concrete countertops, but I’m confused by the different types available. Which type works best for countertop mixes?

Answer:
It’s best to match the type of mixer to the type of concrete you plan on using when making countertops. There are three basic types of concrete mixers available (see photos): drum, mortar, and vertical shaft. All of these types come in a variety of sizes, and some come with a choice of a gasoline engine or an electric motor. Some drum and many mortar mixers are also available with either steel or plastic drums. Here are basic descriptions of how each mixer type works and what concrete mixtures they are best suited for:

Drum mixers are the most commonly used type and what most people picture when they think of a concrete mixer. They have a round drum with fins or vanes fixed to the inside. As the drum turns, the fins move and lift the concrete and gravity causes the ingredients to tumble and mix together. Drum mixers are designed to mix relatively fluid concrete that contains significant quantities of large aggregate. Thorough, efficient mixing depends on the tumbling action of the mixer and on the concrete mixture’s physical characteristics, which can aid in the mixing process. The more fluid the mix, the more effective the mixing action. Typically very stiff low-slump, no-slump, and all-sand mixes are difficult to mix in a drum mixer because they tend to stick to the walls of the drum and not tumble and churn, resulting in the need for frequent hand scraping to remove stiff, clumped material that gets packed against the fins.














Mortar mixers, sometimes called stucco mixers, have a horizontal shaft with paddles attached. The drum of the mixer is semi-cylindrical and remains stationary during mixing. Instead, the shaft and paddles rotate to mix the concrete in the drum. Mortar mixers are designed to mix all-sand mixes, typically used for making stucco or mortar for brick and block. These mixes tend to be stiff and sticky and completely lack large aggregate. Thorough, efficient mixing depends on the mixing action of the paddles and not so much on the concrete mixture’s physical characteristics. For this reason, mortar mixers tend to be more versatile than drum mixers because they can mix both highly fluid and very stiff concrete mixes. And they can usually handle concrete with up to 3/8-inch aggregate. The downside is that stiff mixtures and mixes with larger aggregate can significantly increase wear on the drum (especially plastic types) and on the paddle blades, which often use rubber strips that act like squeegees. Wear is reduced significantly with more fluid mixtures.















Vertical-shaft mixers have wide, shallow, circular mixing pans and are similar to mortar mixers in that the pan remains stationary. A drive shaft rises vertically through the center of the pan, and paddles and scrapers of various configurations move and mix the concrete. These mixers are less common than the previous two types, but they offer increased mixing speed and efficiency and are capable of mixing most types of concrete, both stiff and fluid. The drawback is the discharge method, which may make stiff mixes more difficult to deal with. With drum and mortar mixers, the entire drum is tilted to discharge the concrete. With vertical shaft mixers, the mixing pan is stationary and a relatively small door in the bottom of the pan is the discharge port. The concrete is discharged by opening the door and letting the mixing paddles scrape the concrete over the hole, letting gravity handle the rest.















In summary, if you only work with fluid concrete, then a drum-style mixer will meet your needs. However, if you work with all-sand mixes or very stiff concrete, then a mortar or vertical-shaft mixer may be a better choice.