How Do You Prep A Floor For Screed?

Liquid screeds are not a particular structural feature or element of a building; they are often applied to the flooring or inner roofing surface of all or specific rooms to offer a level, flat, and smooth plane.

It acts as an underlayer to correct sloping issues or rough terrain and provides an extra second layer of support to the surrounding heating elements. Any under-floor heating gets securely placed underneath the type of screed and poured over the top.

Traditionally, you could find levelling screed laid through shovelling screed mix over the surface of heating elements, and they would skilfully level it with a polyurethane float or screeding bar.

These days the process is similar but with a few more steps, making it doable but still a complex ordeal carried out by professionals and experienced contractors.

Unbonded screed tends to be placed atop a type of membrane, such as plastic sheets or others, compared to sitting it directly on top of other substrates and building materials like concrete flooring.

There are a few notable benefits to doing so, including that it can successfully protect your concrete flooring from settling and moisture damage.

First, you must clean the concrete flooring, ridding any grease or dust from the surface as this can prevent your bonding mixture from properly or evenly settling.

Once your flooring is entirely free of debris, dust or dirt, you can begin laying down your choice of membrane or polythene sheets; this helps keep your screed separate from the concrete flooring.

It would be best if you didn’t forget that the sheets need to at least overlap by 20-30cm to ensure protection from mishaps and damage that could come from leakage onto your concrete subfloor. For the same reason, it’s also vital that your sheets or membrane are fitted up the walls by at least 10cm.

Run around the walls with a high-quality form of insulation such as polystyrene or edging foam, which will help avoid damage when your screed begins to shrink during the drying process.

You can also use fibres to reinforce and increase the strength of the screed, as this will ensure all cracking is prevented when your screed dries.

You can also take reinforcement mesh suitable for the screed, and you can lay it over your concrete subfloor; it can sit on top of the screed after being laid.

Laying screed can be a relatively complicated process, depending on the method used. In regards to the level of thickness, the unbonded screed should sit at around 50mm.

We highly recommend that you aim for a thickness of at least 70-75mm when pouring and self-levelling; in doing so, you can account for any height variations from sloping or rough terrain on the subfloor.

All bonded screeds must be a thickness of 35-40mm; however, if your subfloor isn’t entirely level or flat, you must aim for the highest suggested amount. We do not recommend pouring above this level; otherwise, debonding will occur.

To begin the process, we recommend dividing up the floor, as this way, it is a tad easier to work with, especially when striving to achieve a flat, even finish across the entire floor.

Use timber battens, apply a small screed amount to the flooring, and lay the battens atop in strips across the specific section. A great top tip ensures you wet the batten before you lay it on the ground; this makes them much easier to remove.

Once this is done, you can begin laying the screed. We suggest working on the section furthest away from the entrance; that way, you won’t have the tread on the newly laid screed to exit the room.

Then, you can begin spreading it with a high-quality trowel, flattening and compacting it with a straight-edged tool, screed board or vibrating screen board. The best results will come when you do so in a chopping motion.

Once the screen has been laid in that specific section, we encourage you to level the screed with a straight-edge tool or piece of solid timber.

Ensure the tool or timber is laid on the battens to rest on every side, moving down the length in a somewhat sawing motion.

Repeat this process in the remaining sections; after precisely two sections have been fully filled, take the batten out and fill the gap between the two to ensure they are level.

Once the whole floor has been screeded properly, you can finish off the concrete using what is known as a bull float.

Continue this process once all water involved has stopped escaping the concrete or has evaporated. If you wish to, you can successfully create a purposefully textured surface by moving a wooden float across the concrete in arched motions. A steel trowel will help create a smooth finish over the top.

The screed will need to be cured after receiving the final treatment; you can do this by placing a sheet across it and sealing its edges. Ensure you leave the screed for at least seven days to cure fully. However, we recommend leaving it for another three weeks to completely dry before installing brand-new flooring.