Liquid Screed

When it comes to any building, flooring is an essential part of its structure. This means it’s vital to ensure that your floors are sufficiently strong, durable, smooth and level. This can be achieved through screed flooring, but with all the different types available on the market today, you may be unsure as to what one best suits your building’s needs.

There are two main floor screed designs – bonded screed and unbonded screed. To give clarity, specialist concrete contractors Wright Minimix have developed this guide to explain what exactly screed is, the differences between bonded and unbonded screed along with the benefits and uses of each.

Read on to find out more, or contact us today to discuss a screed flooring quote.

What exactly is screed?

Screed is essentially a thin layer that is laid over concrete to create a smooth, sturdy and hardwearing subfloor. Created by mixing cement with graded aggregates and water, screed can be between 25mm and 100mm in thickness, and can be left as a standalone finish or covered with additional decoration (such as carpet or floorboards).

What is bonded screed? 

Bonded screed is laid onto a mechanically prepared substrate (or underlying layer) using a bonding agent or slurry.  The aim is to maximise the potential bond to the concrete substrate. The optimum thickness of bonded screed is between 25-40mm.

What is unbonded screed?

Unbonded screed, on the other hand is intentionally separated from the substrate by the use of a damp-proof membrane or polyethylene sheet. With unbonded screed, it’s crucial that the drying process isn’t rushed as if it dries too fast, the edges of the screed can warp. It’s recommended that unbonded screed thickness exceeds 50mm.

Will screed stick to concrete?

Technically no as screed is not directly applied to concrete. Screed is applied over a mechanically prepared substrate (if using bonded screed) or a membrane (if using unbonded screed) which is placed over the top of the concrete.

What is the difference between bonded and unbonded screed?

We explain the differences between bonded and unbonded screed and when you would use them below. 

When would you use bonded screed?

Typically, bonded screed is ideal for areas that will regularly endure heavy loads such as driveways and car parks.

What are the benefits of using bonded screed?

The advantages of using bonded screed include how:

Bonded screed is simpler to apply as it’s thinner than any other form of screed

As bonded screeds can be much thinner than any other form of screed, this makes the application much simpler as all that’s required is a slurry of cement and water or a bonding agent.

Reduces shrinkage

By applying bonded screed correctly, shrinkage will be reduced in the future due to additives contained in the bonding agent.

When would you use unbonded screed?

As it uses a damp proof membrane to protect against moisture, unbonded screed is best used in buildings where damp presents a serious problem (e.g. for underfloor heating).

What are the benefits of using unbonded screed?

Reasons for choosing unbonded screed include how:

Unbonded screed prevents settlement

Settlement is the term given to when a floor sinks due to large amounts of pressure. Settlement is a common problem with concrete floors, but as the damp-proof membrane separates the screed from the concrete, the risk of settlement is mitigated.

Unbonded screed reduces shrinkage cracking

Shrinkage cracking accounts for about 80% of screed cracking. By separating the screed from the concrete substrate, the risk of shrinkage is greatly reduced during the drying process.

Unbonded screed guards against damp

As already touched upon, thanks to the damp-proof membrane separating the screed from the concrete, a barrier is created to prevent damp rising from the substrate.

Which is better – bonded or unbonded screed?

We don’t believe one screed design is better than the other – it all depends on your project and how you intend to apply the screed; for projects that need to withstand heavy loads on a regular basis, we recommend opting for bonded screeds.

For projects that take place in areas that are prone to moisture and damp, we suggest choosing unbonded screed.

Whether you require bonded or unbonded screed, trust Wright Minimix to provide the right floor solution for your commercial or domestic needs.

Wright Minimix is a specialist concrete and floor screeding company

Wright Minimix specialise in supplying high quality liquid screed flooring, concrete blocks and ready mixed concrete to customers across the South West of England and South Wales. Our team of vastly experienced and skilled concrete contractors pride themselves on giving expert advice across our commercial and residential clients.

To find out how we can provide screed flooring for your property, or to learn more about our wide array of concrete services, don’t hesitate to call our friendly team today on 01179 582090 or alternatively feel free to leave a message on our contact webpage.

Before you can start pouring concrete into your lay site, you need a way to get it there.

In this guide to concrete pumping, you’ll learn exactly how the pumping process works, and why it could be the best concrete transport solution for your business.

If your mix trucks are too large to get close to your lay site, delivering concrete can prove a problem. You could transport the concrete manually, but lugging around heavy cement-filled wheelbarrows is far from ideal – it’s slow and back-breaking work, with a high risk of spillage or injury.

That’s where concrete pumps come in. Concrete pumps streamline the process of transporting concrete, delivering it faster, easier, and more cleanly. They’re able to transport hundreds of yards of mix with ease, cutting down on wastage and speeding up the process massively.

At Wright Minimix, we have a wide range of concrete pumps for hire. These include the largest concrete pump in the UK, standing at 62 metres tall, and the boomless minipump, for delivery to especially difficult-to-access lay sites. If you’re looking for the right pump for your project, get in touch!

How Concrete Pumps Work

Concrete pumps use a simple, reliable mechanism for transporting concrete.

Two cylinders are placed next to one another. Inside each cylinder is a piston: one piston draws the concrete into the cylinder, while the other pushes the concrete out. A valve can be turned to determine which cylinder is open to the concrete hopper and which is open to the discharge pipes.

When concrete is pumped, a layer of water, sand, and cement keeps it lubricated as it moves through the pump line walls. The mix needs to have enough water to move easily through without causing a blockage.

If you’re looking for the right concrete mix for your pumping project, we can help. We’ll create a high-quality custom mix for your project that moves smoothly through pipes while still serving its ultimate purpose.

Types of Concrete Pump

There are two main types of concrete pump: boom pumps and boomless pumps.

Boom pumps use a long robotic arm to deliver ready-mix concrete and liquid screed quickly and accurately. Because of the sheer volume of concrete they’re capable of pumping, they’re often used on large construction sites.

As the name suggests, boomless pumps – also known as ground line pumps – lack this robotic arm. They instead rely on laying pipes from the vehicle to the lay site. Boomless pumps are useful for smaller sites that are difficult for mixing trucks to access.

Looking for more information? Check out our blog post on choosing between boom and line pumps.

If you’re unsure which pump will work best for your project, don’t worry. Whether you need a large concrete pump or a small concrete pump, we can show you exactly which pump will work best for your project.

How the Concrete Pumping Process Works

The specifics of how pumping works depends on the individual situation. However, there is a typical process most projects follow:

1. The pump’s operator sets up the pump and prepares the grout
2. The concrete mixer truck backs into and connects to the pump
3. The operator grouts the line and begins pumping
4. If using a boom pump, the concrete will be laid using the arm. If using a boomless pump, the pipeline must be rearranged during the pouring process
5. Once the concrete has been fully dispensed, the mixer chutes will be cleaned on site
6. Repeat for the other mixing trucks (if necessary)
7. Once completed, the concrete left in the pump and pipeline will be cleaned. How long this takes depends on the length of the pipeline
8. The boom (if present) is reverted back into its travel position and all equipment is packed away. The pump is then driven back to the depot

How to Prepare Your Site for Concrete Pumps

Pumps are excellent at accessing hard-to-reach areas, but they’re more effective when they’re placed as close to the site as possible. It’s important to make sure your site has plenty of room for them and the transport vehicles they arrive in.

If your site is too small or remote to accommodate them, you should plan ahead accordingly. Make sure you’re using a pump that is long enough to reach the site. If you’re using a concrete pumping service, warn them ahead of time so they can account for the obstacle.

Using Concrete Pumps Safely

Pumps are huge pieces of equipment that, if misused, can cause serious injury or death. It’s paramount you take the correct safety precautions when setting up and operating them.

Using Concrete Pump Equipment Safely:

1. Always check for worn couplings or gaskets, as these may let air into the line or allow grout to escape. Wear on pipelines can be checked with a gauge designed to measure the thickness of steel pipe. Make sure pipe ends are compatible with one another, as joints can be dangerous if the ends and couplings don’t match.
2. The pipeline must be properly tied down. Space support brackets every 10 or so feet to reduce stress on the coupling joints, and to transfer the torque to a column or beam.
3. Make sure you’re using the right hose for your application. You should use a specially reinforced hose if you’re using a boom pump. Only place hoses designated as a discharge type at point of placement for discharge.
4. Whenever possible, use water to clean the pipes once pumping has completed. Water is safer and more effective at cleaning than compressed air.

Concrete Pump Vehicle Placement:

1. Before you extend the boom, make sure no obstructions are in the way. For example, power lines, trees, or scaffolding.
2. Power lines in particular pose a big risk. The metal on pumping equipment conducts electricity easily, as does the water present in the concrete mix. Coming into contact with electrified equipment will likely be fatal. If power lines cannot be entirely avoided, you should have a spotter to keep an eye on the boom at all times.
3. Park trucks a good distance away from slopes or sharp drop offs.
4. Make sure the truck is properly stabilised for the type of surface it’s mounted on.

If you still have questions about concrete pumps, reach out to us! We’ve worked on hundreds of pumping projects, and can give you expert advice about choosing and operating the right pump for your project.