Rigid Floats

Note that prolonged or excessive working of the concrete surface early on, especially in the presence of accumulated bleed water, can serve to create a weak upper layer. So too can the trapping of bleed water caused by any premature sealing of the top surface. For this reason, the use of sprung-steel floats or trowels (the action of which tends to close off the surface) is generally inappropriate for preliminary finishing work. Rigid floats are also used in final finishing operations prior to troweling.

Sprung Steel Floats and Trowels
Used in the final finishing operations (after the completion of bleeding and the onset of appreciable stiffening) to close off the concrete surface, impart smoothness, and provide for the later development of good wearing resistance. The actual waiting period required from the time of initial placement to the point of readiness for steel floating will depend on the material make-up (e.g. the cement and water contents) of the concrete mix and on the prevailing temperature conditions. A delay of somewhere between 1 1/2 - 4 hours is typical for relatively warm weather, 5 - 8 hours in colder weather.

Sprung steel floats & trowels

Most steel-bladed finishing tools can double as floats (blade held flat to surface) or trowels (blade angled to surface). Note that the greater the inclination of the blade as it is drawn across the concrete (and the smaller the area of the blade) the greater is the amount of local pressure that can be put on the surface. Do not incline the blade to any significant extent until such time as the concrete is capable of sustaining the associate pressure, otherwise some gouging and/or tearing of the surface could result. As the concrete continues to stiffen, progressively adjust the angle of the blade to suit or switch to a smaller/narrower blade. The use of blades with curved end (rather than sharp corners) for the final troweling operation lessens the risk of leaving unsightly trowel marks.

Edging Tools
Used in pavement work to produce a rounded edge detail (this being far less prone to chipping or breakage in normal service than an abrupt sharp edge). The concrete should be relatively stiff (but not too stiff!) when an edging tool is employed. Edging tools create a very neat border for broom-finished areas.

Edging Tool Grooving Tool

Grooving Tools
Used to produce control joints in concrete slabs and pavements. Control joints allow for the effects of later drying shrinkage and thereby decrease the risk of unsightly random cracking. In order to function properly, the groove should be of a depth no less than one-third the local concrete thickness. If the grooving tool does not cut to such a depth in the first instance this can always be increased after the fact through the careful use of a trowel blade or similar implement. (A second pass of the grooving tool may then be required to tidy up the joint).

Do not let the concrete become too stiff before grooving. A grooving tool can normally be used as soon as the bleeding has ceased.

Guidence on positioning of control joints in concrete Pavement/Ground Slabs?/Paths

General:

Corners:

OR

Changes of Width/Geometry, Re-entrant corners:

The maximum spacing of control joints is often taken as the lesser of 4m or 1 1/2 times the width of the slab/pavement. Where a concrete slab/pavement is laid around an existing structure or takes some irregular form (L-shaped.T-shaped, etc), be sure to provide an appropriate control joint at all inside (re-entrant) corners. The overall pattern of control joints should serve to create a series of square, rectangular, and/or triangular areas.

Disclaimer:
While the information presented within this web site is offered in good faith, Holcim (New Zealand) Ltd disclaims any and all responsibility for the application of the principals and procedures discussed.