Floor screeding is a highly skilled trade. The art of laying a floor, generally over large areas takes a lot of skill and is hard work.
Traditionally floor screeding is the process of mixing cement and sharp sand to a ratio of 1:3-
Below is a brief outline of the most popular screed types.
Traditional Sand and Cement –
Fully bonded – the screed mixture is laid directly to the substrate surface.
Surfaces on which the screed is to be laid, needs to be thoroughly cleaned and a suitable bonding agent applied prior to installation. Bonding agents can be cement slurry, PVA, Epoxy Resin or SBR. These products fulfil different purposes so the use of application needs to be carefully considered.
It’s important to note here that if the substrate surface is not suitably cleaned of all debris and dust the bond between the substrate and screed can fail. Bonded Screeds are usually laid at a depth of between 25mm to 50mm.
Unbonded Screed –
Unbonded Screeds are usually laid at a depth 50mm or more.
Floating – Sheets of rigid insulation are laid between the substrate surface and the screed. As with unbonded screeds a perimeter up-
Floating Screeds are usually laid with a minimum depth of 65mm.
Finish – Can be left, or can be power floated for a smooth finish.
Level – Suitable to be laid level or to falls in areas where run off is required (i.e. in a wet room)
- PPF Fibres (Reinforced Screeds) are often added to the screed mix to give added strength and minimise the risk of cracking.
- In a similar way, wire of steel mesh can be laid into the screed for increased structural strength.
- Polymer (Or Polymer Modified Screeds) can be added to screed mixes in large quantities to provide additional benefits such as increased water and chemical resistance, strength, and reduce the minimum depth requirements.
Advice should be sought from the manufacturers of these products prior to use.
- There are also several plasticisers and binder products (Fast Set and Fast Dry Screeds) on the market that can be added to a screed to reduce the drying or setting time.
- Aggregates (Granolithic Screeds), such as small chippings of granite of between 4mm to 8mm for example, can be added to screeds to increase the strength for high traffic or heavy duty areas, and to reduce the depth of the screed. For heavy duty or lower depth screeds, professional technical advice should be sought.
There are several factory mixed sand and cement products that can be delivered to site ready mixed.
The advantage ready mix screed products have, is the consistency and accuracy of the mix, and it often comes with shorter drying times, and increased durability.
Due to the watery consistency of these products, special care needs to be taken with the preparation of the surface to which it is to be laid. You can be sure that any small gaps in the substrate or DPM will be found by this liquid screed mixture! All joints need to be lapped, and taped, and everything checked and checked again prior to pouring.
Liquid Screeds have numerous benefits over traditional screeds:
- Faster installation – up to 2000m2 per day
- Quicker drying times
- Can be laid at Reduced Depths (40mm on insulated unbonded floors compared to 65mm traditional)
- Improved compression and strength
- Increased Thermal conductivity – especially with underfloor heating
- Minimal Shrinkage
Important to note that these screeds do not like damp or wet areas which can cause extensive damage to the screed, this includes from leaks and flooding.
There are numerous manufacturers to choose from when looking at Self Levelling Flow Screeds, and we recommend you take advantage of their excellent technical advice lines when choosing the product that is right for your project.
There are different types of screed pumps, pan mixers, forced action pumps that accommodate the variables in traditional sand and cement screed, and liquid flowing screeds. It is imperative that you speak to a specialist manufacturer of this type of plant to ensure that you are using the correct one for the product you intend to use.
Screed Plant can be highly pressurised potentially dangerous equipment with lots of moving parts, and should only be used by trained and competent persons, and with all the safety features and guards in place in accordance with the manufacturer instructions.
The appropriate PPE is essential for screeding. Cement can cause serious chemical burns. Be careful.
Join FATE as a member for a host of helpful tools, sign off sheets, risk assessments, method statements – where to find a supplier and more.
Check out the FATE Free Advice page for further help.