FATQs - Frequently Asked Technical Questions

We get asked all kinds of weird and wonderful technical questions here at Screed Giant, and our technical geeks always love getting to grips with interesting queries. The following FATQ’s or Frequently Asked Technical Questions and answers are some of the more common (and a few less common) enquiries we’ve had.

If your query is not answered below, or you need further technical support, please feel free to get in touch using the form at the bottom of this page or by calling us on 01606 214201.

There are such a large choice of screeds available we would need to know the following to provide the correct advice:

  1. What is the substrate (Is it concrete, or something else?)

  2. Do you know if the substrate is dry?

  3. Is there anything else that needs to be incorporated? (e.g insulation, underfloor heating)

  4. How thick do you need the screed to be?

  5. What will be the final floor finish?

  6. How quickly do you need to lay the floor finish?

*Note –This is the most fundamental question, so it may be easier to give us a quick call*

There are several options:

  1. In the market there are many proprietary admixtures that can be added to traditional screed to reduce drying times.

  2. There are “Special cements” also known as cement replacements that’s can be used instead of OPC, to improve drying times.

  3. Pre-blended bagged screeds, to which you just add water. Some of these have very fast drying times.

  4. There are some specialist screed materials that have extremely fast drying times, however these products can be costly.

*Note – some of the above options provide additional properties to the screed, for example strength.*

free flowing screed is a self levelling or self smoothing compound.

For typical traditional screed thickness information, please refer to BS8204. However, many propriety screeds can be laid thinner in accordance to the specific manufacturer of the screed being used.

Coverage rates can vary for every product. We always recommend going off the coverage /consumption section of the technical data sheet. If you require assistance with calculating the amount using the coverage rate, please contact us on 08081 696887 and we will be happy to help.

Traditionally, it has been the case that screeds have had to be overlaid with a floor finish to provide a wearing surface. However, we now offer products with abrasion resistant surfaces, which can be left uncovered. Often, although not always, these are designed as industrial finishes. More recently products have been created to be fashionable for decorative finishes.

The market changes daily and there are some specialist products that have entered the market, that do advertise as thermal screeds. At Screed Giant, we offer a large range of products suitable for use in insulation and screed systems. Please call for advice on your project.

The temperature of the background must be 5 degrees c and rising until it hardens on external applications.

Epoxy resin floors, including RonaFloor epoxy coatings, are frequently used on floors for animal accommodation because they are easily cleaned, if they’re not scattered with slip resistant sand. They are also impervious to liquids and resistant to attack by chemicals in animal waste. Kennels are a typical example.

Epoxy coatings typically can receive foot traffic after approx. 24 hours, and full chemical cure is approximately 7 days, and therefore exposure to cleaning products/water etc should be limited in this period.

Care should be taken when considering application of coatings to tiles. Coating is not usually considered until tiles are in poor condition, when adhesion of the tiles may be suspect, or if tile grout may be loose, friable or incomplete. Light mechanical abrasion is required to obtain good adhesion, especially when treating half or fully glazed tiles, as this may cause debonding of the tiles from their bed. Coating should only take place if adhesion of the tiles is certain and the condition of the grout is good.

Within an underfloor heating specification, it would be recommended to use a screed suited to the system or admixture for the system. You can then use an abrasion resistant screed such as an industrial floor screed as the final finish.

In practice, we believe it unwise to use a levelling compound or adhesive containing cement on a calcium sulphate system. Adhesives and levelling compounds suitable for use on calcium sulphate are available on our website.

*Note -Please don’t hesitate to contact us to discuss calcium sulphate brands available.*

Most types of underfloor heating systems can be introduced to heat after 7 days. Some proprietary screeds can allow this to be sooner, but in all cases the system should be brought up to working temperature gradually.

We have a wide range of products available, and will always try our best to source products that we may not have on our website. Simply give us a call on 08081 696887 between the hours of 8.30am and 5.30pm.

You can have almost any finish on top of UFH, just as long as the floor recommendations from the manufacture are adhered to. Usually, it would be a requirement that the Underfloor heating should be commissioned and turned off again prior to the application of a finial floor finish.

Drying times will vary depending on what type of screed you are using: whether it’s a cement replacement, additive or self smoothing compound. It is important to keep the building conditions in mind too. We would also recommend looking at the technical data sheet on the product for a rough guide on approximate drying time.

These are common issues screeds may face. The screed drying process takes place from the surface down, this resulting in a tendency for the screed to curl upwards at the edges. It is also possible for the screed to undergo shrinkage within the drying period.

The extent of shrinkage cracking and curling of screeds are influenced by:

  1. Drying conditions – It may be necessary to control this, and the drying time, by covering the screed with polythene – this is known as curing.

  2. Mix proportions– Excessive amounts of cement or water in a screed mix can be harmful to the screed, and cause the screed to be more prone to curling and cracking.

  3. Bond strength – The tendency of screeds to curl upwards at the edges during drying is generally resisted by the bonding to the substrate and the thickness of the screed. Bonded screeds have less risk of curling and cracking.

  4. Thickness of the screed – Thicker screeds have more strength to resist the curling force.

This is a complicated question, since the recommendations vary depending on the type of screed and egg crate system you are using. There are so many underfloor heating systems out there, and the thickness of the screed required may vary depending on the secure bond between the system and substrate. In all instances, we would recommend keeping the system as flat as possible.

We offer two types of egg crate system, both of which come with and without insulation.

Egg crate systems which do not have holes in, cannot be secured to the subfloor and are therefore classified as a floating system. Where a levelling / flowing screed, or a cement replacement is being used, this would require the screed to be laid at a depth of 50mm minimum*^. Where a traditional sand and cement screed is being used, the minimum required depth would be 65mm^ for domestic applications and 75mm^ for commercial applications. This is to ensure no future risk of cracking.

If the egg crate system has holes in it, the screed bonds through the hole onto the insulation or subfloor. Where there is an insulation panel attached, this should be secured using glue or screws. A levelling screed can then be used at a minimum depth of 25mm^, or a traditional screed at 65mm^ for domestic applications or 75mm^ for commercial applications.

*There are a select few products which may allow this to be reduced to 40mm, please call our team for advice if you would like further information.

^Always refer to the manufacturers’ data sheets for guidelines. Application depth may vary between products.

Where a substrate has Bitumen / Asphalt on it, and it cannot be removed, we would usually recommend using Ardex Arditex NA or Larson Lartex NA, both of which can be applied directly to the Bitumen, without the need for a primer. In either instance, it is vital to ensure that the flooring grade asphalt/bitumen is in good condition and that there are no signs of de-bonding and/or hollowness and to make sure the surface is dry and free of any contaminants before laying.

If the Bitumen is soft, but cannot be removed, we would recommend applying a traditional floating sand and cement screed, at a minimum depth of 65mm (or according to the manufacturer’s guidelines for a floating system), to compensate for any movement within the Bitumen.

No. Resin bound surfacing must not be laid onto modular paving systems as independant movement of the blocks/slabs will cause cracking.

For light foot traffic resin bound surfacing may be laid at increased thickness (40mm) onto well compacted type 1 or type 3 hardcore. This method is not suitable for vehicular traffic.

Yes. Resin bound surfacing is suitable for vehicles upto 7.5 tonnes as long as the underlying base is suitable.

Aggregate must be washed and kiln-dried and be specifically graded for use in resin bound surfacing.

No. A forced action mixer with a minimum capacity of 120 litres must be used to ensure adequate mixing.

General cleaning is to be carried out by lightly jet washing. Refer to the resin bound surfacing cleaning and maintenance guide

No. All blends are tested for slip resistance and all have a low risk of slip category

Airborne noise is transmitted by air and atmosphere, for example a television, a dog barking or people talking.

Impact noise is when an object impacts on another, for example a person’s footsteps or an object being dropped on the floor.

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