What is screed?
A screed is a thin layer of specialised concrete that is usually poured over a concrete floor base, sometimes over underfloor heating, to create a smooth, level surface that can accommodate the final floor covering such as carpet or tile.
What is screed made of?
Most screeds are made from cement and sharp sand for a fine screed, or cement and a coarser quarter inch aggregate for heavy duty or industrial screeds.
Are there different types of screed?
Yes. There are four different types of screeds, although screeds can be tailor made using a range of mixtures to provide different qualities.
- Bonded screeds are fully bonded to the prepared concrete surface or substrate using specialized bonding agents or primer. This results in a thinner screed.
- Unbonded screeds are laid onto a damp proof membrane or polythene sheeting, which separates the final layer of screed from the the concrete base substrate. This type of screed is usually applied to older concrete substrates.
- Floating screeds are laid onto a layer of thermal insulation, which is usually on top of a damp proof membrane that separates the existing concrete substrate.
- Underfloor heating screeds are the same as floating screeds, but they arelaid over underfloor heating pipes instead of insulating material.
What does screed do?
Screeds are used to level out a concrete surface or substrate. Screeds provide a smooth and even finish that is better for laying flooring, such as carpet or tile. It can also be used to cover insulation or underfloor heating pipes, offering a thermally efficient solution.
Why is laying screed important?
Screeding gives a smooth and even surface over a substrate that could be uneven and unsafe. As a rule, the level of the floor surface should not vary by more than 0.20" over the space of 10 feet, and a correctly laid screed can ensure this.
Can I pour screed over concrete?
Yes - the main purpose of screed is to pour it over a concrete substrate.
What is the difference between concrete and screed?
Both concrete and screed are made up of cement, aggregate and water, but screed is a smoother, more free-flowing mixture made with finer aggregate. Concrete is coarser containing more aggregate material and coarser aggregate material. The extra aggregate gives concrete additional strength and durability.
How long does screed take to dry or cure?
Different types and thicknesses of screed take different lengths of time to dry or cure. Just poured screed should be left untouched at least 24 to 48 hours before you try to walk on it. Special additives can reduce this time to 12 hours. For heavier traffic, such as moving furniture or tools across the floor, leave the screed untouched for five to seven days. Most screeds will reach their fully cured strength after 28 days, so for best results, wait as long as you can to use the screeded surface.
How soon can I tile on screed after it has been installed?
Since screeds can shrink as they dry or cure, you should allow your screed to fully cure before laying tiles. For best results, wait 28 days before you lay the final floor covering.
Is screed suitable for all types of floors and all types of properties?
Yes. Screed can be used in residential, commercial, industrial premises. If the screed will be subject to heavy wear, the mixture can be adapted to withstand the additional weight and traffic.
How do you level screed?
Floor screed should be poured directly into the required location, then use a straight-edge wooden float to level it. Find four level points and pull the float across the surface using the level points as the guides.
Self-levelling floor screeds can also be used. These have a more free-flowing consistency.
Does sunlight damage screed?
If the screed is laid in direct sunlight or extreme heat, it should be protected with a tarpaulin or plastic sheeting to prevent it drying out too soon.
Can you pour screed in any weather?
Floor screed can be poured in wet and cold weather as long as the outdoor temperature remains a few degrees above freezing. If the temperature is close to freezing, you will need to take precautions to ensure the best results. Since most screed is laid indoors, the precautions involve taking extra care when transporting and storing materials, ensuring the area is water tight, and ensuring the screed has time to completely cure before being used.
Is screed self-leveling?
Traditional screeds are not self-levelling, however, many modern screeds can be self-levelling.
Can screed be a final floor finish?
Yes. Many people choose to cover screed with a wide range of floor covering, from carpet to tiles. In commercial environments it is often more cost effective to leave it exposed. Also, a modern interior design trend for industrial-style minimalism has lead many homeowners to choose screed as the final floor finish.
I’m having under floor heating fitted - do I need screed?
Yes. Screed is the ideal flooring solution for underfloor heating. The screed protects the heating system and retains the heat for longer making it more economical to use.
Do I need screed for paving?
Screed isn’t essential for laying paving, but it does offer additional benefits, such as a tidier site and less time and manpower. A simple retarder in the mixture will keep it workable all day so you can lay your paving slabs on top.
How do you care for screed?
Screed should not require maintenance or care. As long as it is laid correctly, the screed shouldn’t develop flaws or faults.
What are the advantages of mixing screed on site with a mixer?
There’s very little difference between ready-mixed or on-site mixed screed, but they each have their own advantages. Ready-mixed saves you time while on-site mixed offers greater flexibility.
Do I need to screed a concrete floor?
Yes. Without screed, it will be difficult to get a concrete floor level enough for a floor covering.
What is the minimum screed thickness?
The minimum thickness at which you can lay your screed depends on the type of screed and your application. Some heavy duty applications require thicker concrete to ensure its strength.
- Bonded screed thickness: minimum 25mm approx.
- Unbonded screeds thickness: minimum 50mm approx.
- Floating screed thickness: minimum 65mm approx.
- Underfloor heating screed thickness: minimum 65mm approx.
What thickness screed do I need for a garage floor?
For applications that will experience heavy use, such as in a garage where a vehicle will be parked or on underfloor heating, a floating screed with a minimum thickness of about three inches is usually best. Every application is different.
Is screed soundproof?
Screed mixtures can be tailored to offer acoustic insulation.
Can screed be used outside?
Screed can be used outdoors although most people prefer to use concrete as it is easier to install and offers enhanced strength and durability. That said, screeds can make jobs like outdoor paving much easier.
My floor is uneven - will screed make it level?
If the concrete floor is in good condition and just a bit uneven, screed can be the ideal solution to level it out if installed correctly. If the floor is very uneven or damaged, it's best to redo the floor.
Can screed be pumped?
Screed can be pumped directly to your location using a specialised screed pump. The alternative is chute delivery, which is used most of the time.