Drying times - how long does screed have to dry?
- Five screed types in house construction
- cement screed
- Poured asphalt
- Calcium sulfate screed
- Synthetic resin screed
- After curing comes the drying
- Which screed dries how long?>> Measures to accelerate the drying time
Nothing is more annoying than to have unwanted traces and impressions in the fresh screed. Therefore, the drying times for screed must be strictly adhered to and always be understood as a minimum. The specified drying times also include other factors that are difficult to assess by a layman. The temperature of the environment (inside and outside), the humidity, the layer thickness and the type of screed also play a major role in the calculation of the drying times.
Terminological subtleties around festering
The term "drying times" is not entirely correct when it comes to the time between insertion and passage of the screed. The hardening of a screed layer is not caused by the evaporation of water, but by chemical processes that take place in its interior. Otherwise screed would be resolvable by applying water. For Magnesiaestrich that's true too, but that's another case. Cement-bound screed does not dry, it " sets off ". Synthetic resin screeds and plaster screeds " harden ". The distinction is important to understand that the input water is important for the curing process. Attempts to accelerate the curing time prematurely by high temperatures can therefore have fatal consequences.
Five screed types in house construction
The most widely used screed is still very popular because of its universal usability. It is suitable for indoor as well as outdoor areas. With appropriate additions, the cement screed can be arbitrarily color and technically adapted to the desired requirements. Cement screed can be earth-damp and installed as floating screed. In addition, it is - in conventional design - with 2.50 € per 25 kg bag very cheap. Cement is cured relatively quickly.
The setting process is completed after 24 hours until the soil is firm. Still, he is still very sensitive. The visit was to be maintained for a week to ten days. DIN specifies a curing time of 21 days for cement-bound materials, which includes concrete and mortar as well as screed. Additional heating only makes sense according to the established rules. Adequate ventilation shortens the subsequent drying time and prevents mold growth. A nail test can provide information about whether the screed is hard enough for entry: If the screed can be scored deep with a fingernail, it is still in the middle of the curing process.
The still largely unknown in private application mastic asphalt screed used as a binder bitumen. The flowability of the mastic asphalt screed is achieved by heat. Is the poured asphalt screed cooled, he is walkable.
Calcium sulfate screed
Calcium sulfate screed uses gypsum as a binder. This makes it more flowable and increases the self-leveling properties of the screed. Calcium sulphate screed can also be installed quite thick as liquid screed and is therefore well suited for underfloor heating. As a material, calcium sulfate is good-natured and does not necessarily require a reinforcement. However, it is recommended.
Calcium sulfate screeds, which are introduced as liquid screed, have a very high water . Their hardening happens extremely fast. Most of the calcium sulfate screed is already accessible a few hours after introduction. But then exact steps must be kept to make the drying process optimal.
Magnesia screeds consist of a mixture of organic substances such as wood chips and caustic magnesia as a binder. It is built in bulk. After installation Magnesiaestrich is indeed quite fast walkable. But it must be professionally sealed immediately after curing. Since it is strongly hygroscopic (water attracting), even the smallest splashes of water can ruin the magnesia screed. The sealant layer must cure for 2-3 days . Care should be taken to ensure adequate ventilation.
Synthetic resin screed
Synthetic resin screeds consist of three components: aggregate, solvent and hardener. The solvent ensures that hardener and aggregate can mix with each other. Then it diffuses out and lets the synthetic resin screed harden. This happens relatively quickly, so that after 2-3 days of synthetic resin screed can be committed. Adequate ventilation is essential, otherwise there may even be a risk of explosion.
After curing comes the drying
In addition to the basic type of screed, the manner of its installation is crucial for the drying time. A water-based screed, which is installed damp, is much faster hard and walkable than a liquid screed. The longer the drying time of a screed, the higher the risk of cracking. The process of drying must be as homogeneous as possible. If too much heat is applied to the fresh screed due to external irradiation, tensions may arise that cause cracks.
The fact that a screed is firm enough to commit damage free, but does not mean that he is cured. Screed needs enough water or hardener to harden. What is too much diffuses out. For this, the screed must have a long enough opportunity. As screeds are insulated down through the shell floor, and the dam layer, water and solvent can only escape upwards . Too early sealing by vapor-tight coverings such as PVC, laminate, tiles or carpets can have fatal consequences: Mold formation or, in the worst case, chemical reactions between solvent and flooring always entail expensive repairs.
The expert speaks of the so-called "compensation moisture". This is achieved when the residual moisture in the screed matches the average humidity of the environment. If the screed dries up to this point, the residual moisture remains in the screed and is not further diffused to the outside. It is easy to determine whether a screed is dry: Cut a square out of transparent foil with an edge length of 30 cm and glue it to the floor. The underside of the film must be hermetically sealed. If there are no more condensation droplets under the foil, the screed is completely dry.
Further workable screeds are thus after their setting and curing time. But minimum times must be respected.
Which screed dries how long ">
The longest drying time have flow marks. The high water , which is necessary for the flowing introduction of the screed, must escape again by diffusion. Cement screeds are quite robust and undemanding in their drying behavior. On the other hand, calcium sulphate screeds are much more sensitive and require compliance with defined work steps:
- Immediately after insertion:
The screed must rest and must never be entered for the next 48 hours . Windows and doors must be closed, as the screed must be protected against drafts and direct sunlight.
- After 48 hours
Open all windows and ensure maximum ventilation.
- Calculate drying time
For flow screeds, the drying time is in square with the layer thickness. The rule of thumb for the drying time of flow screeds is
Days of drying time = d² x 1.6
Tabular this means:
- 1 cm layer thickness = 2 days drying time
- 2 cm layer thickness = 7 days drying time
- 3 cm layer thickness = 15 days drying time
- 4 cm layer thickness = 26 days drying time
With four centimeters of layer thickness you are just in the minimum thickness for underfloor heating. However, this formula is only useful as a rough guide. Natural and artificial factors can significantly increase the drying time for the liquid screed.
Measures to accelerate the drying time
- Use quick binder
Quick Cement hardens much faster than normal cement. Once cured, quick-setting cement can be dried out in no time with massive measures such as heat radiation, ventilation or switching on the underfloor heating system. However, this has its price: fast cement costs about 10 times as much as normal cement.
- Professional heating and ventilation
To speed up the drying process professional equipment can be used. The DIN EN 1264 part 4 regulates exactly how a heating process has to run for the drying of a screed. For this purpose, mobile heaters can be used, if the specified in DIN heating and cooling periods are met. Although electrically operated devices have much higher operating costs. But since they run emission-free, their operation indoors is much less dangerous than gas burners.
Tip: More recommendable is the use of professional building drying equipment
A new Bautrockner costs about 600-1600 euros, depending on the equipment and performance. Professional building dryers have a built-in hygroscopic sensor, so that the residual moisture can always be accurately determined. The rental prices for professional building dryers start at about 30 euros a day. This looks cheap at first. But if you look again at the drying times, which occur at larger layer thicknesses, the purchase and subsequent sale of a professional construction dryer can be the cheaper solution.
- Use underfloor heating skillfully
DIN EN 1264 also regulates the use of underfloor heating to speed up the drying process. This is advantageous in that thereby the function and tightness of the floor heating are checked with the same. Cement screeds can be heated at the earliest after 21 days, calcium sulfate screeds at the earliest after 7 days. Overall, the drying time of flowing screeds can be reduced by 30-50% with the help of these measures.
The residual moisture can be determined with the film test or a moisture meter. Only when the maximum permissible residual moisture values are reached can the flooring be introduced.
Tips for quick readers
- Setting and curing is not always the same
- Only cement and calcium sulphate screeds need to be dried
- Drying time of liquid screed increases with the thickness of the layer squared.
- DIN EN 1264 regulates how the drying process can be accelerated
- Electric fan heaters are preferable to gas and gas burners. Even better are professional building dryers
- Calculate the need for building dryers in advance and then decide on a purchase or rental solution.
- skilful construction site planning bridges the drying times of the screed with other work.
- Wallpapering and painting are possible, for example, even if not completely dried screed.