Understanding Floating and Darbying

Finished concrete is intended to be flat and floating helps achieve that. It is important to float the concrete before excess moisture or bleed water rises to the surface and accumulates. Excess water can significantly weaken concrete; therefore, floating must occur before too much water bleeds to the surface. It is normal for some surface water to accumulate, which should be allowed to evaporate before further floating. Let’s cover some useful tips on which tools to use, and when.

 

Why Use Floats and Darbies?

Floats and darbies help ensure that concrete is properly screeded and floated, which is essential to a proper finishing job. The voids or holes in the concrete left by screeding are leveled out by floating. The float process also embeds the coarser aggregate in the concrete that may have risen to the surface ensuring a smooth finish. In general, two passes of the float should do it.

 

Floating Is A Tricky Business

Floating does not completely close the surface of the concrete, which allows all that excess bleed water to be removed after the slab is floated. While floating needs to be done immediately after screeding so less water rises to the surface, it also should not seal the surface so much that the bleed water gets trapped beneath. Trapped bleed water can cause dusting or delamination. Floating the surface of the concrete takes a steady hand keeping the bull float as flat as possible. Skimming the bull float flat on top of the surface prevents pushing the concrete around and sealing the surface.

Pro Tips for Floating and Darbying

Bull floats, hand floats, and darbies all accomplish the same task: they further smooth out a concrete slab after screeding. Bull floats are held when standing and have extendable handles, while hand floats and darbies are typically hand-held tools that workers use while kneeling (long handles can be attached to some darbies).

While these have different applications depending upon the size of the slab, they can all be used on the same slab. Tips for using each of these include:

Bull Floats

• Begin using immediately after screeding before bleed water surfaces
  
  
• Hold the bull float flat on top of the concrete surface, keeping the leading edge slightly elevated. However, do not tilt the float. It’s a fine balance here.
  
  
• Never dig the bull float into the concrete. It has a long surface so it can make wide passes up and down the slab.
  
  
• Avoid making high spots along the edges of the forms. To do this, push or pull the bull float all the way to the edge as possible. (Go back after with a darby to float these edges)
  
  
• Avoid over-floating or allowing concrete to spill over the sides of the forms.

Hand Floats

• Hand floats are used (after bull floats) to finish the floating process
  
  
• They can get into unfinished tight areas around edges and obstacles
  
  
• Hold hand floats as flat as possible, using a wide semicircular motion
  
  
• Both hand floats and darbies prepare the slab for troweling

Darbies

• Begin using immediately after screeding before bleed water surfaces
  
  
• Keep darby flat against the surface of the slab
  
  
• Use a sawing motion across surface
  
  
• Use one or two hands to push or pull the darby around the wet concrete (some darbies have one handle, others two)

Learn about Different Types of Floats and Darbies