Floor Preparation

Prepare Your Floor For Liquid Screed (Anhydrite)

The building should be weather tight prior to the pour. The roof should be covered and all external doors and windows in place. Alternatively, all openings are to be made weatherproof with clear polythene. Remove all dust and debris from the floor surface and leave free from contamination. Remove any debris or mortar splashes from the sub floor.
Place insulation in 1 layer. This is often Celotex, Kingspan or expanded polystyrene. Using dried sand to fill the void around pipes and ensure that this is level. Boards must sit evenly, ensuring that all high/low points are removed from the sub-base and that the installation boards are laid flat, without rocking and be tightly packed, so they are stable when walked on and staggered and tightly joined. Insulation boards are often slightly curved. If this is the case, lay the boards so they are curved downwards (higher in the middle) to minimise rocking. important to note; Where there are service pipes running across the floor, such as gas pipes, the insulation should be grooved on the underside to allow the pipes to sit within the insulation, rather than leaving the boards resting on top of the pipes.
A membrane of 1000 gauge or thicker should be laid over the entire floor, covering the insulation boards. Ensuring it is pulled tight with no air pockets or creases and free of any punctures. Overlap joints at a minimum of 100mm and seal with non-metallic tape such as gaffer tape to avoid any leakages. Allow the membrane to run up the walls to above the full depth of the screed (150mm would be more than enough), to create a bath. Make sure that the polythene fits tightly into the corners, securing with additional edging tape. To create a bath like effect, which is watertight to stop any liquid screed escaping and getting underneath the insulation, if the screed gets under the insulation, then it will all start to float and will be a disaster!
Once the insulation is installed, any vertical surface coming into contact with the screed, such as walls, stairs or pipes, should have a foam insulation edge strip stuck to it securely. This is to allow for any minor expansion once the screed is dry. There are various types of strips, but they are typically 8mm-10mm thick and come in rolls. Please take care to ensure it is neatly placed into the corners at 90 degrees to avoid air pockets. Tack the edging strip to the walls using a staple gun as required to hold it in position. If there is a plastic skirt attached to the perimeter strip, use gaffer tape (non-metallic tape) or adhesive spray to stick it to the membrane – this stops the screed from getting behind the perimeter strip and pulling it away from the wall. Again, avoid creating air pockets between the screed and the insulation/wall.
Where door openings or level changes are found, these should be provided with a temporary framework. So, the perimeter edging strip can be laid on top.
Any shuttering across doorways or steps should be fully sealed with expanding foam or mastic to prevent leakage after laying but before setting. Pipe ducts or holes through walls also need to be sealed before placement of the liquid screed.
Important to note: the membrane is not there to act as a damp proof membrane but to stop the screed from escaping when poured.The floor is now ready for the screed to be laid. It is imperative that this preparation is carried out to the highest standards. The neater the prep, the neater our screed results are!

When We Arrive to Install

Setting The Levels – We will work from a place called a datum point. Typically, this will be from the stairs, but can also be from other areas such as a doorway or threshold. We will then set out levelling gauges called ‘tripods’ and, using a laser, will set them to the correct depth to make sure that the finished screed surface is level throughout the building.
Installing Screed – The screed will then be pumped in and poured to the depths set by the tripods. Once this is done, the tripods are removed. To make sure that it is smooth, without any tide marks or air bubbles, we will then agitate the screed using a dappling bar. The installation is then complete.
Requirements – We will require an outside tap and a washout bay/skip, away from the area of screed. As detailed in the section General.

Common Mistakes To Avoid When Preparing For Your Liquid Screed

Measuring the space incorrectly

Often sub-floor slope or unevenness may cause unexpected differences in the overall floor level and in the quantity of screed required. It is the customer’s responsibility to measure each room/area appropriately.

You will need to consider critical features such as door openings, minimum thicknesses/cover and required differentials in floor height between rooms. It is very important that you must ensure your sub-base is adequate to take the additional weight of the screed, as this is not our responsibility.

Prior to installation, the required depth must be marked on the wall above the level of the finished screed, so that they are present for comparison should a disagreement be raised about finished floor levels.

Any such disagreement must be brought to our attention within 48 hours of the screed being laid. Should these marks be removed or altered prior to any investigations then we will not be held accountable for any level issues.

Ordering less screed than required

Should extra liquid screed be required over that originally ordered and a separate delivery needed, the client will be charged extra costs, so it is essential that your measurements are accurate to avoid this.

Installing Liquid Screed With Underfloor Heating

All pipes and cables for under floor heating should always be installed to the manufacturer’s guidelines and spacings.
Install on top of the tanking membrane, not beneath it.
All heating pipes are to be firmly fixed to the insulation using supplied clips/staples, piercing the insulation. The clips are self-sealing so will not leak when liquid screed is poured.
Install underfloor heating pipes and ensure they are appropriately fixed at every 400mm along the length of the pipes more frequently on bends. It is important to note; that there should be no unfixed lengths of pipe or cable greater than 400mm long, as if they are left unfixed, all under floor heating elements will float to the surface of the screed. Flo Pro Southern is not liable for the securing of the pipes.
Pressurising the system should take place prior to the installation of the screed. This allows any issues/sign of leaks to be addressed by your fitters ahead of our installation.
Make sure that the system is full of water prior to the liquid screed being laid. This avoids the pipework floating to the surface of the screed. It also means that your pipes are expanded in preparation of the screed and therefore avoids any expansion issues from the heat once the screed cures.
If you are using an ‘eggbox’ type pipe system, the membrane should be laid under the eggbox, and you should avoid using small off-cuts of eggbox to avoid any possibility of floating.
The minimum cover above underfloor heating pipes is 30mm therefore minimum screed thickness is normally 50mm when using.
After you have read through this guide, if you have any other questions about your preparation, please don’t hesitate to contact us, as we will be glad to answer your questions 0118 229 3366.

Bay Sizes and Joint Requirements Heated Maximum

Heated

Movement joints should be placed at Door Thresholds, between independently controlled heating zones and where heated and unheated screeds meet.

Heated

General

The customer shall protect any thresholds or edges the pump pipes may be laid over getting the pipeline to the job.
The customer shall also protect any surfaces they do not want to be compromised by splashing as this may occur during laying. This is especially important for finished surfaces (walls, windows and staircases etc).
Expansion joints shall be placed in positions specified by your floor design engineer. It is important for foam perimeter expansion strips at all intrusive corners such as doorways and other features such as fireplace hearths, staircases will help to reduce the potential for cracks to develop at these points.
Please note that we will need to wash our pump out (which contains the remaining product) on site before leaving. It is the customers responsibility to provide a suitable area or washout receptacle and for the final disposal of this waste.

Contact Us for Advice on Screed Type and Pricing

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