When installing ceramic tiles, vinyl, carpets and other flooring. Self-levelling screed level off uneven substrates and creates an even flat surface that you can connect to.
Before laying self-levelling screed, its suitability has to be assessed. The majority of projects will comprise three distinct kinds of substrates that are as follows:
Construction Types
Bonded is a crucial aspect of self-levelling screeds laid by layers because it is based on the bond that is formed with the substrate. Self-levelling screed is ideal for this kind of construction.
Unbonded refers to the fact that there is a membrane between the screed and its substrate. This kind of structure is not one that would work with this kind of screed.
Floating construction refers to the fact that the screed is placed on insulation, either thermal or acoustic insulation. This kind of construction is not one that is appropriate for this kind of screed since bonding is usually required.
Sound Substrate
When it comes to bonding, I think it is essential to draw attention to the process. When we look towards the material, it must to be solid. When we refer to “sound,” it needs to be sturdy. If you notice cracks, crumbling or any other issue, it is imperative to take action prior to placing the screed. It is not a good idea to installing self-levelling screed over something that’s not stable since it can cause the screed to crack and/or deteriorating.
Contamination
The screed should be checked to make sure that the substrate has not been affected. Contamination could be caused by a range of things: dust, grease, oils and anything else that could have been absorbed into the crevices in the screed (the capillaries of the screed). If there is contamination, it might require a mechanical surface preparation. This could involve grinding, scabbling, or shot blasting. If there is any paint on the substrate, then it must be removed prior to the installation of self-levelling screed.
The surface should be cleaned and vacuumed if there is dirt or dust over the area. Prior to laying the self-levelling screed, a primer must be placed on the substrate to facilitate the bonding between the self-levelling screed to the substrate. Sometimes, it is possible to lay without primer, but always be sure to read the directions prior to laying. In any case, you’re going require some penetration into the surface. It must bond to the matrix, which means that you need to remove the initial couple of millimetres of the matrix in order to reduce it to a level that can bond.
In the case of made of power floated concrete The top layer of the matrix has to be removed in order to be able to access the more open texture of the concrete which allows the primer to get into. Certain types of concrete can be poured directly on the power floated surface however it is necessary to examine the requirements for each specific product. In general, you’d be looking at changing mechanically the surface so that it can allow for more adhesion between screed as well as the surface.
Self-levelling Screed Thickness
When you lay self-levelling screed the thickness will vary between different products however, as a general rule of thumb, check the depths below:
The minimum depth is typically 2-3mm There are products that are able to go to “featheredge”
The maximum depth is around 10mm However, when you add bulking aggregates (normally dry sand that has been kiln dried) when you lay self-levelling screed, it can be as deep as a of 30mm.
Substrate Moisture
Generally speaking, when you lay self-levelling London, the surface should be at 75 percent absolute humidity, or lower. when it is above a membrane that is liquid damp proof may be required to reduce the moisture available.
I would suggest that the surface be examined for moisture prior to any work.
Primer/Bonding Agent
If you are completely satisfied that you are completely satisfied with your substrate you’re prepared to put on the primer, which aids in the bonding between the screed to the substrate.
Each product comes with an approved primer that has been tested and may come with different ratios to water. Always verify the manufacturer’s guidelines prior to implementing.
The primer generally needs to dry prior to laying self-levelling screed. However, it shouldn’t be left for too long (always be sure to check the product’s directions).
Applying the primer, use the brush, and be sure there’s no poolsing in the prime.
Screed Mixing
When mixing by hand with an electric drill you add the powder to right volume of water (again take note of the manufacturer’s instructions for the product they sell) While mixing until a non-clumpy mortar is formed.
It is poured on the substrate, and laid self-levelling screed. It is then spread using a trowel made from steel or floating floats to make the mortar spread and then finish.
The screed is likely to self-smooth within during the initial 15 mins. It will last for a total period of about 30 minutes subject to the temperature at the site.
Drying Times
Conditions on the ground can affect drying times, but 3 millimetres of screed will typically be dry within 24 hours and walkable within 3-4 hours.
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