Gypsum screed: frequently asked questions
What is a gypsum screed floor?
Gypsum (anhydrite) floor screed is a self-levelling floor compound made from natural and recyclable ingredients. Gypsum screed is cement-free, and with it you avoid the usual floor screeding problems, such as shrinkage, heavy weight and dust containing allergens.
When can you walk on the poured floor and continue work?
After 24 hours, you can walk on the floor and continue with lighter work. The floor can take full load on the third day. After five days, you can start using the underfloor heating.
How is it done?
The floor compound is pumped through a hose onto the floor from a mixing unit mounted on a truck. The amount can be controlled very precisely. After the compound is pumped onto the floor, it is smoothed and left to dry. The compound is not pumped at high pressure. The work leaves the site clean.
Where is it done?
We work across Estonia, but we have also worked in Finland, Sweden and Latvia.
How strong is the poured floor?
The strength of gypsum screed floors reaches about 38N/mm2, the same as concrete floors.
How thick is the screed layer?
For a monolithic floor, from 20mm.For a floating floor, from 30mm.When installing underfloor heating, the screed layer above the pipes should be 30mm.
Does the floor need reinforcement?
A gypsum screed floor needs no additional reinforcement or fibres.
How do you prepare the floor for pouring?
The insulation under the floor should be as level as possible. The underfloor heating pipes must be fixed securely. Ideally with clips directly into the insulation (EPS). Make sure there are no cracks or holes in the floor where the screed could flow through.
Why is the minimum thickness of gypsum screed so much smaller than that of cement screed?
Knauf floor compounds are plastic with low thermal expansion, and the compound contains a very strong binder. A 35 mm layer of gypsum screed has the same properties as 75 mm of reinforced concrete.
The design specifies an 80mm cement screed. Can I use gypsum screed instead?
Yes. Depending on the construction stage of the site, there are different options, but the simplest is to increase the thickness of the insulation layer under the floor by as much as the gypsum screed layer is thinner.
Can a gypsum screed floor be used in a timber house?
A gypsum screed floor is an excellent choice for floors in timber buildings. Thanks to its strength and lightness, gypsum screed suits both the ground floor and the upper storey. A gypsum floor is elastic and has very low thermal expansion, so it also suits log houses well.
Is a gypsum screed floor fire-resistant?
In timber houses, it is extremely important to achieve the highest possible fire resistance. Gypsum screed floors have the fire resistance of class A1 building materials.
How much does the finished floor weigh?
With a 35mm screed layer, the floor weighs under 70kg/m2, which is several times less than a conventional concrete floor.
Sound insulation of gypsum floors?
A gypsum screed floor has much better sound insulation than concrete floors, especially against low-frequency impact noise. A standard gypsum screed floor with a thin insulation mat a few millimetres thick already gives 35dB of sound insulation.
Can gypsum screed be laid on a wooden floor?
Yes, gypsum screed can be used both to cover an old wooden floor and on boarding/OSB etc. in a new building. With underfloor heating, we recommend a thin insulation layer under the screed to improve thermal resistance and keep heat from spreading in the wrong direction.
Can gypsum screed also be used as a levelling compound?
Yes, it can. You can even pour a layer just a couple of millimetres thick.
How long does the work take?
The work on site is a relatively fast process. We can pour about 1000 m2 of floors per day.
At what construction stage is a gypsum screed floor poured?
As with a conventional screed floor, the building envelope must be closed and a minimum temperature of +5C (outdoor temperature down to -15C) must be ensured during drying. However, you can also pour at a much later stage of construction (for example after plastering), as drying takes many times less time and the heating can be switched on after just a few days. In addition, compared with concrete screed, the work is practically clean: it does not leave lots of compound stains and splashes behind or, at worst, “power-floating” marks on the walls.
Is gypsum screed also suitable for outdoor use?
Gypsum floors are intended for indoor use.
Can underfloor heating be used with gypsum screed?
For a heated floor, using gypsum screed instead of concrete screed is not only possible but highly recommended – gypsum screed has better thermal conductivity than concrete, plus a much smaller total mass, which eliminates one of the main drawbacks of underfloor heating – high inertia. When a room heats up quickly (for example, spring sun starts shining into the room) or cools down, a large concrete mass usually reacts to the temperature change only hours later. A thinner gypsum screed floor with better thermal conductivity reacts to changes many times faster. In addition, a gypsum screed floor is free of concrete’s age-old problem – high thermal expansion and the cracks that often come with it.
If you install underfloor heating, what is the best way to fix the heating cable or pipes?
Out of old habit, people tend to fix the pipes/cable to reinforcement (since a concrete floor needs it anyway). As a gypsum screed floor needs no reinforcement, it makes sense to fix the pipes/cable to the floor with clips or fixing tape (which one exactly depends on the subfloor; ask info@porandavalukeskus.ee for details). Using reinforcement is not recommended, as it usually increases the required screed thickness and costs much more than fixing clips and tapes.
How should the construction site be prepared?
On site, we need 3x20A electricity and clean water at a flow rate of 1500l/h (normal household water pressure).
Which floor coverings is gypsum screed suitable for?
All conventional floor coverings can be used on gypsum screed.
What is the lead time?
In most cases, we can do the work within 1-2 weeks.
How often are expansion joints needed?
Because the thermal expansion and drying shrinkage of gypsum screed are practically non-existent compared with concrete, a typical private house needs no joints. For larger areas, discuss the need for joints and their placement with our specialists.
In summary - why choose a gypsum screed floor?
- Fast installation
- Lets you start using underfloor heating quickly
- Work can continue the very next day
- No waste – exactly the required amount of compound is mixed on site
- The product has all the necessary certificates
- Excellent thermal conductivity and the even heat distribution that comes with it
- No “power-floating” needed
- No “laitance” forms
- No dust
- Hypoallergenic
- Good sound insulation
- Clean work
- Screed thickness with underfloor heating from 35mm
- A thinner screed layer and good thermal conductivity allow faster and more precise room temperature control, avoiding over- and underheating
- The screed surrounds the heating pipe/cable on all sides, which gives noticeably better heat transfer than dry installation
- The gypsum screed installation process minimises the risk of damaging the pipes
- No expansion joints needed
Need an approximate price?
Fill in our enquiry form, stating the type of site and the total floor area to be screeded.