When installing ceramic tiles, vinyl carpets and other flooring. Self-levelling screed smooths out uneven substrates, leaving a flat, smooth surface to connect to.
Before laying self-levelling screed, its appropriateness needs to be assessed. The majority of projects will comprise three distinct kinds of substrates according to the following:
Construction Types
Bonded is a crucial aspect of the self-levelling screed laid because it is based on the bond formed with the substrate. Self-levelling London is ideal for this kind of construction.
Unbonded is when you have a membrane between the screed and its substrate. This kind of screed isn’t something that could be appropriate for this kind of screed.
Floating construction is when the screed is placed on insulation, whether it’s thermal or acoustic insulation. This kind of construction isn’t something which is suitable for this kind of screed because the bonding process is typically required.
Sound Substrate
When it comes to bonding, I think it is crucial to emphasize the process. If we are looking towards the material, it must to be solid. When we talk about “sound,” it needs to be a solid. If you notice cracks, crumbling, or any other issue, you must take action prior to placing the screed. It is not a good idea to placing self-levelling screed on something that’s not stable as it could cause the screed to crack or separating.
Contamination
The screed should be checked to make sure that the substrate isn’t affected. Contamination can come from a range of things: grease, oils, dust or anything else that has 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 are any traces of paint on the substrate, it should be removed prior to the installation of self-levelling screed.
The surface must be cleaned and vacuumed in the event that there is dirt or dust over the area. Before you lay self-levelling screed,, a primer should be placed on the substrate in order to aid in the bonding between the self-levelling screed to the substrate. Sometimes it’s possible to go down without primer. Always check the instruction before you lay. In any case, you’re going require some penetration into the surface. It must bond to the matrix, which means that you have to grind away the initial couple of millimetres of matrix to grind it down to something that can be bonded.
In the case of made of power floated concrete and the top layer of the matrix has to be removed in order to allow for the more open-textured concrete, which will allow the primer to get into. Certain types of concrete could be placed directly on the surface that is power floated However, again you must examine the requirements for each specific product. In general, you’d be considering changing the mechanical properties of the surface in order to facilitate greater adhesion between the screed as well as the surface.
Self-levelling Screed Thickness
When you lay self-levelling screed the thickness can vary between different products but as a general rule of thumb, look at the following depths:
The minimum depth is usually 3mm There are products that are able to go to “featheredge”
The maximum depth is around 10mm but by adding bulking aggregates (normally kiln-dried sand) when you lay self-levelling screed, it can reach a depth of 30mm.
Substrate Moisture
Generally, when installing self-levelling screed, the surface should be at 75 percent absolute humidity, or lower. when it is above the threshold of a liquid damp proof membrane might be necessary to block the moisture available.
I would suggest that the surface be checked for moisture prior to proceeding.
Primer/Bonding Agent
Once you are satisfied that you are completely satisfied with your substrate you’re in a position to use the primer, which helps in bonding the screed to the substrate.
Every product will come with a tried and tested primer, and may come with different ratios to water. Always verify the manufacturer’s guidelines before using.
The primer generally needs to dry prior to laying self-levelling screed. However, it shouldn’t typically be allowed to sit for more than a few hours (always be sure to check the product’s directions).
For applying the primer, make use of a brush and make sure that there isn’t any concentration on the primer.
Screed Mixing
When mixing by hand with an electric drill you add the powder to appropriate volume of water (again follow the manufacturer’s instructions for the product they sell) while mixing well until a non-clumpy mortar is formed.
It is poured on the substrate, and laid self-levelling screed. The screed is then removed with a trowel made of steel or floating float to distribute the mortar and then finish.
In general, the screed will self-smooth within about 15 minutes. It will last for a total period of about 30 minutes dependent on the temperature of the site.
Drying Times
The conditions on the site will affect drying times, but 3 millimetres of screed will typically be dry within 24 hours. It would be walkable within 3-4 hours.
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