There are many types of concrete screeds out there these days. But what is the best concrete screed for pouring flat projects like parking lots, driveways and floors? And which is the best concrete screed for the type of pours that your company does most often? We’ll break down the pros and cons of each screed, but first, let’s talk about what a screed is, what it does, and why they are necessary.
What is a Concrete Screed?
In a nutshell, a concrete screed is a straightedge tool that levels and smoothens the surface of freshly poured concrete. They can be powered by gas, electricity, hydraulics or operated by hand. Screeds are typically made of aluminum, magnesium, steel or wood – though there are exceptions. As a screed passes over wet concrete, it pushes large aggregate down and brings “creme” to the surface. They leave concrete surfaces smooth, flat, and free from any deformities.
Concrete forms are usually used around the outside perimeter of the pour. These forms keep the wet concrete contained until the concrete has cured enough so that the concrete can stand on its own. Most concrete screeds use these forms (or a screed pipe) as a guide when leveling or “striking off” the surface of the recently poured slab. Forms are generally set to a particular height with the use of a laser. The screed then rides on the forms leaving the finished concrete slab at exactly the desired height.
Why is it Important to Screed Concrete?
Screeding is a highly important process when pouring flatwork projects like driveways, floors or parking lots. A contractor that doesn’t cut any corners can pour strong, beautiful slabs that will last for decades to come. As a screed passes over of concrete, it levels the surface of the concrete. Most screed either vibrate or spin – working larger aggregate down, just below the surface. This leaves smaller sand and cream (a thin slurry of cement) on the surface that finishers can work with to build a smooth, professional-looking finish.
Equally as important as a smooth, level surface is a smooth, level base. Concrete is like glass. It bends, it flexes, it freezes, it thaws. Imperfections, like a scratch on a windowpane or a rock chip in a windshield, cause weakness and give the glass a place to break easily when stress is applied. This is precisely why contractors place control joints in concrete. If the concrete is going to crack, contractors want to control exactly where that crack will be. If the subgrade is wavy, with high spots and low spots, then weaknesses are created in the underside of the slab and a contractor loses control over if and where a slab will crack.
What is a Slump Test and How Does Water Content Affect Concrete?
One of the most important factors in the strength and longevity of a concrete slab is the slump at which it is poured. A concrete slump test is a simple measurement of how much water is present in uncured concrete. It measures the ratio of water to the concrete’s other ingredients – aggregate and cement. A low slump has relatively low water content and a high slump has relatively high water content.
Concrete’s water content (at the time of pouring) is directly related to its strength. The wetter the concrete is poured (or high slump), the weaker the cured concrete will be. While water is essential to the curing process, it is destructive in excess amounts.
Adding water to a concrete mix dilutes the mixture. That dilution causes the cured concrete to be more susceptible to shrinkage. As the water in the mix dries, it also bleeds to the surface – squeezed up under the weight of the concrete itself. Those channels created as the water escapes the slab are micro-cracks in the slab itself. These micro-cracks are weaknesses within the slab and over time, through settling and freeze/thaw cycles, they will often become significant cracks.
At the University of Illinois, the Department of Materials Science and Engineering found that “too much water reduces concrete strength, while too little will make the concrete unworkable”. This is the problem that contractors face every day: wetter concrete is easier to place. So they find themselves cutting corners – making their finisher’s job easier, but sacrificing the slab’s strength and durability in the process. Pouring at a high slump doesn’t just damage the integrity of the slab. It can also damage a contractor’s reputation and their hopes for future business.
What are the Different Types of Concrete Screeds?
Concrete contractors are responsible for deciding what is the best concrete screed type for their company or for a particular pour. There are many different types of concrete screeds available on the market and each one has its place. Let’s take a closer look at each.
Concrete Screed Comparison Chart
|Screeds 20+ Feet Wide||Ø||★★★||★★★||★★★||Ø||Ø|
|No Dragging Required by Laborers||★★★||★★★||Ø||Ø||Ø||Ø|
|Ease of Use||★||★★★||★||★★||★★||Ø|
|Operates to Left, Right or Center||Ø||★★★||Ø||Ø||Ø||★★★|
Laser-guided screeds are great for jobs that require high flatness specifications. Set up as a laser-guided arm on a relatively small machine, they’re capable of precision level concrete with minimal labor. Crews get concrete somewhat close to grade and laser-guided screeds will level to a precision grade from there.
But there are downsides to laser-guided screeds too. First, they’re extremely expensive – usually costing from $100,000 to $250,000. Second, the widest laser-guided screeds available on the market max out around 20 feet wide. Nearly none of them are capable of grading the gavel base.
Given the big price tag on a new model, a used laser-guided screed may be a better introduction to this equipment. Prior to purchasing, you should inspect any used laser-guided screed thoroughly because you will often incur significant cost if they break down. There is also a limited number of folks out there that are capable of repairing them if they do. Keep in mind too that breakdowns almost always happen on pour days – never when the machine is sitting idle. So there is a real possibility of losing a pour if your equipment does break down on the job.
Laser-guided screeds save on physical labor and are extremely accurate, but their cost is far more than most can afford. Many contractors choose to rent laser-guided screeds instead of paying the heavy price tags associated with buying and maintaining their own.
One of the fastest ways to screed concrete is the Dragon Screed system. Dragon Screed is easy to set up and extremely easy to use. Its versatility allows crews to screed gravel and concrete in many different configurations – up to 32 feet wide. Dragon Screed levels gravel or sand subgrade quickly and accurately. Crews no longer have to drag gravel in order to have a quality subgrade. Once the gravel is level, simply remove the subgrade panels and switch to the vibrating floats. You then use the same equipment to screed the concrete.
Dragon Screed, like a laser-guided screed, requires little to no rakers in front of the screed – crews simply pour the concrete close to grade and the equipment does the rest. Machine driven, Dragon Screed allows crews to pour concrete extremely low slumps without having to fight to get it flat. If you want to screed the concrete a second time, it’s as simple as backing your machine up and driving along the forms again.
Dragon Screed has a unique patent-pending vibration system. Both the screed bar and each individual float has its own vibrator. A remote control operates the vibrators allowing them to work together. With five different intensity settings, contractors can adjust vibration up or down at any time as needed. The vibrating floats work the concrete, bringing the cream to the surface and making finishing the concrete a much easier job.
Dragon Screed works in forward or reverse and off of either side of the machine. It can also be configured to work directly in front of the machine. Dragon Screed eliminates the need for draggers in front of the screed, drastically reducing much of the manual labor associated with pouring and screeding concrete (see concrete project profitability analysis). Your crew can focus their energy and attention on finishing concrete behind the screed.
Unlike other screeds, Dragon Screed also levels subgrade material like gravel or sand. With adjustable subgrade panels, adjustable from 4 to 12 inches, Dragon Screed gives contractors a near-perfect subgrade. Creating a uniform slab on the bottom side of the slab. This uniformity in the slab is hugely important and often overlooked. More attention is generally given to the surface of the concrete because this is what the customer sees, but this approach is short-sighted ultimately leads to a low-quality final product. A flat subgrade leads to a slab that is uniform in thickness and therefore stronger.
Truss Screeds / A-Frame Screeds
Capable of pouring concrete at widths all the way out to 60+ feet, truss screeds or A-frame screeds can put a lot of concrete down – if you have a crew large enough to help drag. Truss screeds are generally gas-powered and are pulled by a winch attached on both ends of the screed.
Truss screeds are very heavy and require a lot of labor to set up, tear down and clean. They run relatively slowly and if you happen to leave the concrete a little low in one spot, setting the screed back to strike off again is extremely difficult. You’re generally better off fixing any mistakes by hand.
Truss screeds, like roller screeds and stand-up screeds, require a lot of laborers keeping the concrete close to grade in front of it – and those laborers work hard for every inch. The problem with this is each raker has a different idea of how much concrete is just right (or they just work at different paces). That is, one raker has their area almost the perfect height for the screed. The next raker, however, has the concrete too high and the one next to them has the concrete too low.
As the rakers fight to get the concrete to the right height in front of the screed, they often end up pushing or pulling concrete too close to the screed. When this happens, they actually affect the level of concrete BEHIND the screed. If rakers are not careful, they can cause concrete to boil under the screed, creating high and low spots. Unless the screed is set back and that section of the pour is screeded again, those waves can be difficult to remove with a bull float.
Roller Screeds / Spinning Screeds
Roller screeds or spinning screeds allow concrete crews to get into small areas with ease. Typically set up as a metal tube that spins away from the operators, roller screeds work reasonably well on small pours. They allow crews to pour on steep grades or even use contoured rollers to pour gutters.
Roller screeds are operated by two laborers that pull against the spinning screed while the other laborers grade the concrete by hand in front of the screed. Since roller screeds are human-driven, they require a great amount of physical labor. If you’re pouring anything more than a truckload or two, roller screeds quickly become a lot of work to operate – especially when pouring at lower slumps. Roller Screeds are powered to spin, but leveling the concrete comes down to brute manpower.
When concrete is left too high or is poured at a low slump, roller screeds have a tendency to throw concrete over the top of the screed. In this case, in order to avoid a wavy slab, the two pullers have to carry the screed back. That section of concrete then gets screeded again.
Although the spinning effect of a roller screed has some cream-creating abilities, there is no vibration in roller screed systems. Vibration is key in allowing the aggregate to settle, bringing a small amount of cream to the top. Unless a contractor vibrates the concrete separately when using a roller screed, proper consolidation is unlikely.
Lightweight, affordable and easy to clean, roller screeds are an option for tight areas and small pours. Being human-driven, roller screeds require a lot of labor to pull the screed and rake concrete.
Another great tool to have on hand, stand-up screeds work wonders on very small pours and in tight areas. Stand-up screeds are typically set up as a vibrating bar that is operated by a single user. One worker drags the screed while several others are out in the concrete, raking as close to grade as they can get. Stand-up screeds are readily available and easy to find on the cheap. A fair amount of physical labor is still required and they are limited in width, slope, slump, and speed.
And last but not least, the simplest, cheapest option for screeding concrete – the good ole screed board. Generally made from a nice sharp 2×4, a screed board is the simplest solution for screeding concrete – just don’t try to do too much with it. Screed boards operate with one person on each end. They work together to push and pull the board back and forth in a sawing motion while maintaining continuous pressure forward. Choose a board that is straight. If your boar is warped, your concrete will reflect that by leaving either a crown or rut in your slab.
Screed boards are sufficient for short, narrow flatwork projects like small sidewalks or patios. Anything larger than that and you’ll find yourself working way harder than you want to. Bending over while making a sawing motion and trying to pull the screed board all at the same time will wreak havok on even the toughest finisher’s spine.
What do the Best Concrete Screeds Have in Common?
All good screeds have one thing in common: they do their job well if they are kept in good condition. Any screed that is bent, dented, has dried concrete left on it, or doesn’t run well, is not going to perform well and the finished concrete will show that. It is important that screeds are kept well-maintained and in good working order. If your beat-up old screed isn’t fast, easy to use, and leaves a beautiful, professional finish, then it may be time to consider upgrading your equipment. After all, a high-quality finished product is the most important thing for your customers.
*The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement