Wednesday, November 14, 2012

How To Create Surface Textures With Concrete

There are many standard surface textures for concrete and there are a lot more you can "invent". To get an idea of why such possibilities exist it would be helpful to take a look at a cross section of a concrete slab. Correctly poured, spread and finished, the cross section would reveal an almost uniform pattern. The larger stones in the mix would be surrounded by smaller stones and spaces between w fashion coats ould be filled with the finest aggregates (sand). Each piece of aggregate would be encased in cement which bonds to itself and bonds aggregate to aggregate.

Working with a wood float is a finish in itself or it can be just a step in preparing the surface for a slick finish accomplished with a steel trowel. The wood float finish leaves a rough, slip-free surface which is practical for many purposes, especially on walks and paths where traction is an important consideration. The steel trowel finish can be made almost as slick as linoleum and this is good for interior slabs that will be overlaid with tiles or which will be used as is - for a recreation room that will be used for dancing, for example.

When you have an idea for a particular texture, construct a small test slab to see if the results match your expectations. The test slab does not have to be large; stepping-stone size will do. The important thing is that you carefully note the contents (proportions) of the mix, amount of spreading and tamping, time lapse between striking (if any) and the finishing touches. Go through this procedure even if you have to make three or four test slabs. They can always be used as stepping stones.

Striated Surfaces

Striations can take the form of straight, zigzag or wavy lines and are usually used to add some interest to a nonskid textured surface. A long handled broom can be used for the purpose or a small hand brush. Stiff bristles will produce a coarse texture while soft bristles result in a fine texture.

You can finish with a broom or brush over a floated surface or a troweled one. The float-broom finish will always be coarser than the trowel-broom finish. Straight lines are done by resting the broom on one edge of the pour and then pulling toward you. Each time you do as much as the width of the broom. You can jiggle the broom as you pull it or move it in such a manner that you create a wavy effect.

Travertine Effect

This is a very intriguing texture which involves an extra operation after the surface of the concrete has been broomed. The brooming is to insure a good bond when for an additional mortar coat.

To make the mortar coat, use a sack of white Portland cement with 2 cu. ft. of sand. Add about 1/4 1b. of color pigment and mix thoroughly. Any mineral oxide color can be used, but yellow is extremely effective. Add enough water so that the mix will pour like heavy paint.

The coating is thrown on the slab with a brush. The best method is to pick up a good quantity and apply it to the slab by snapping the brush. A quick flick of the wrist does it - a snap that causes the mix to leave the brush and strike the slab smartly. The idea is to make an uneven surface with depressions and ridges that are from 1/4 to 1/2 in. high.

Allow the coat to harden until you can rest a board across it for working and use a steel trowel to flatten the ridges. The result is a kind of three-dimensional texture that is smooth in some areas and coarse-grained in the depressions. You can vary the results by the amount of final troweling you do and/or the amount of finish mortar applied. The final effect is most pleasing if the slab is then scored in a uniform or random geometrical pattern before the concrete cures.

This is just a small sample of the surface textures you can create with concrete.

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