Screeding concrete is a process where wet concrete is levelled to the proper depth, typically with a steel trowel, and finished with another tool.
Concrete finishing tools can be made out of aluminium or stainless steel for use in exterior settings where strength and weather resistance are important. Hand screeding concrete is not usually used for large projects. A self-propelled motorised screed can be used to finish a large slab, typically with the assistance of other tools.
The screeding process begins by placing the fluid concrete in position with a pump or other method. The material is typically placed between forms, which are then removed when it has solidified. If not careful, workers can potentially damage the wet concrete by using the wrong tools to remove the forms, especially if they are not soft enough to avoid tearing or scratching the surface of the fresh concrete.
Screed rails are installed at the edges of each section where it meets adjacent sections to create a straight edge so using the screed rails that successive slabs line up properly without interrupting joints between them. Screed rails are typically made from steel channel shaped stock and have holes drilled along their length for attaching temporary guide boards called 'screed stops'.
A screed stop board is a wallboard sized and cut to the distance between a concrete form and a screed rail. The stop boards are attached to one or more steel stakes driven into the ground at intervals along the base of the forms. Other types of tools are a screed board, straight board and power screed
A variety of tools can be used to perform this task, including various aluminium or stainless steel trowels, float blades, square shovels, bull floats and squeegees. In large projects, it is common for workers to use an automated powered screed that is guided by rails laid out in advance on which stops have been placed at regular intervals.
A manual tool called a 'bull float' may also be used with a separate tool called a 'squeegee' to partially cure high spots before power finishing takes place. As the concrete is worked it may be necessary to add or remove water (if too dry) or add portland cement (if too wet) in order to correct its workability.
Depending on the particular use of the finished product screeding can take place anywhere from a few minutes after placing until several hours afterwards, so long as it remains in a plastic state before hardening begins. In a typical residential setting, a final finish layer might receive minimal hand screeding after being floated and immediately followed by steel troweling for added durability and gloss. The Australian Government's Your Home website has a handy guide to concrete.In commercial projects, however, multiple layers of material might be applied fairly rapidly with very little waiting time between them before adequately curing each layer before adding the next one. This would especially apply if the application was for a concrete floor and flooring surface, either for inside or outside use.
A power trowel is a motorised device that has a rotating steel blade and a strong vacuum system to suck up excess concrete from the concrete floor while it's being smoothed. When the machine moves across an area of wet concrete, its blades scrape the surface flat and excess concrete, removing the high spots and allowing any excess cement mix to be sucked into its pan. In addition to making the concrete surface a smooth surface , power trowels serve other purposes including shaving off ridges or stamping designs into the surface for decorative effect. In order to screed a concrete slab successfully, you need to have an understanding of a variety of different factors which can influence the project, including how water affects the mix design, how temperature will affect setting times and what different tools are available to help make the process easier. A good screed finishing process requires a certain amount of experience with the use of various tools to properly prepare the surface, which benefits greatly from being watched over by an experienced supervisor who can adjust techniques during the process.
Screeding is normally done when the concrete has sufficiently hardened enough that it can support its own weight, but not so much that it cannot be worked. It also needs to be free of laitance, which is a layer of powdery material on the surface.
To prevent this from forming, properly mix your batch using dry materials and make sure you don't skimp on water or skip adding chemical mixtures. Also, wait until there are few if any foot or vehicle traffic in the area since they will leave impressions behind in freshly set concrete which are difficult to remove later by screeding.The most common time for screeding is about 24 hours after pouring concrete, just before cure and concrete finishing process.
Concrete is usually cured by misting the surface with water twice a day. The goal is to keep it moist and let any excess moisture slowly evaporate, which can be done in several different ways:
Placing plastic sheeting over the concrete and periodically spraying it.
Using a slow-release dampening system that automatically sprays every few hours on an automated timer.
Creating an enclosed space where humid air is released while the concrete cures inside of it (also called a hot box).
Concrete finishers use a variety of different tools to achieve the desired effect, depending on the type of surface being created. Some examples include squeegees for large flat slabs or rubber trowels for stamping designs into pre-mixed concrete.
Depending on what type of surface is being prepared, either hold the screed directly over the centre line of the slab or in a straight piece parallel to it.
Screed bars can be made of wood, aluminium or steel, but avoid stainless steel which is typically too slippery. The depth of the screed should depend on how much material needs to be removed and how deep it is based on your experience with the type of concrete you are working with.
Generally speaking, any depth that leaves between 1/8" and 3/16" will produce a flat surface with no visible horizontal lines after it dries. To remove stringy laitance from the area being worked on, scrape off any ridges using a broom or stiff push broom before screeding over them again.
Begin the process by placing the leading edge of the screed bar at one end of where you want to start forming a level surface and use the same setting on both sides. Bend your knees and start by pushing down in front of you with a slight forward motion that will result in a product that is level with one another.
The screed bar should be held parallel to the concrete until just before it reaches the opposite edge, at which point you should veer off slightly so that it is angled back towards the centre of the slab. Be sure to go slowly and keep your arms and spine straight so as not to exert too much pressure on them. It's a little different to honed concrete.It takes about ten passes over an area to properly smooth out uneven spots after it has been screeded. The last pass, known as skimming, consists of holding the blade almost flat against the top and dragging it over to create a perfectly even surface.