Types Of Finishes To Concrete

Sapuram Nikhita

Shreya Satish

Shadari Athrey

Sathvik Y

What is finishing?

Finishing is the operation of creating a concrete surface of a desired texture, smoothness and durability. The finish can be strictly functional or decorative.

Why finish concrete? Finishing makes concrete attractive and serviceable. The final texture and hardness depends on the concretes end use.

Formed and off-form surfaces

• Formed: A surface requiring formwork to provide shape and texture finish to the concrete.

• Unformed: A surface that does not require formwork to provide either shape or finish to the surface, eg the top surface of slabs or pavements. These surfaces generally have to meet two independent tolerance criteria: the ‘flatness’ of the surface and variation from the designed elevation (levelness).

Finishing of formed surfaces

• Smooth Form Finish: The form facing material produces a smooth, hard, uniform texture on the concrete. Surface textures that result from forms with raised grain, torn surfaces, worn edges, patches, dents, or other defects are ground smooth or otherwise repaired.

• Air Voids on Formed Surfaces: Air voids on formed surfaces deeper than ¼ inch have to be filled with patching mortar.

• Rock Pockets: Poorly consolidated concrete is removed to sound concrete and the defect repaired.

• Immediately after removing the forms, form ties are broken back a minimum of ¾ inch from the surface, honeycomb, voids, and other surface defects grouted. The surfaces are then thoroughly dampened and rubbed with a carborundum stone for a rubbed finish. Cement wash may be alternatively applied.

Finishing of unformed surfaces

• Slabs: Screed with straightedge to remove low and high spots bringing the surface to the required finish elevation of slope and float with a steel float at least three feet in width. When the concrete has reached its initial set, finish with a steel trowel. Leave finish essentially free of trowel marks, uniform in texture and appearance and plane to the correct tolerance.

• Finishes that are exposed and subject to foot traffic receive a broom finish with a texture of plus or minus 1/16 inch.

• Tops of Walls with Bearings: Strike smooth tops of walls and similar unformed surfaces that shall have bearings or bearing pads, and finish with a steel trowel.

• Stairways and Sidewalks: Strike smooth tops of stairs and sidewalks and finish with a light broom providing a texture of plus or minus 1/16 inch.

• Slabs with Waterproofing Membranes: Strike smooth and float finish. • Construction Joint Surfaces: Surface shall be broom or raked finished. Surface shall be

water or grit blasted prior to placing additional concrete, such as columns on column footings and column footings on reservoir slabs.

Method of finishing

• To obtain an even surface on walls after the formwork has been removed a cement wash is brushed into the surface in 2 coats.

• The area to be coated should be thoroughly wetted before the wash is brushed on. This coat is rubbed in with a wooden float.

• The finished surface is sprinkled with water 2 to 3 times a day for 3 days, for if the wash dries before it has set it may dust off.

• A better appearance is obtained if the wash is rubbed with a carborundum stone.

Rubbed finish

Cement wash

Cement wash

• The simplest form of concrete paint is cement wash which is a slurry made up of cement and water (about 14 kg/100 sqm) and applied with a white-wash brush. This does not stick on for long though it may be improved by addition of fine sand.

• Lime, calcium chloride or common salt may be added to the cement and water slurry to make it stronger and improve the adhesion.

• Before applying any form of cement wash or paint the concrete surface is cleaned and free from any oil, grease, dust or loose material and is well wetted as curing is essential to ensure complete hydration of the cement base.

Surface finishes

• Very pleasing effects may be obtained by the use of lining of wall board, plywood or hessian cloth. Mouldings and decorative features may be produced by fixing appropriate insets in the shuttering.

• Where hessian cloth is used it should be of a very coarse texture as otherwise the wave pattern will not be reproduced. It should be well stretched and turned over the edges of the shuttering.

Form lined concrete

Rubbed finish

• As soon as the formwork is removed the surface is thoroughly wetted and then rubbed with no.20 carborundum (SiC) stone using plenty of water. The rubbing will remove board marks.

• Rubbed surfaces are washed clean and small voids filled with cement mortar 1:2.

• The first rub is applied while the concrete is still green, preferably 24 hours after placement.

• Where necessary , joints may be filled with plaster or clay.

• Exposed concrete surfaces which are to be plastered are roughened with wire brushes and raked out closely with chisels after the formwork is struck off.

Exposed aggregate finishes

• This can be achieved by removing the outer film of cement from the concrete to expose the aggregate.

• Best results can be obtained by the usage of rounded aggragates of size 10mm to 24mm

• A wide variety of finishes may be obtained on the concrete surfaces with cement mortar which may consist or either

(a) One part cement and three parts sand

(b) One part cement ,1.5 parts of lime and 6 parts sand.

EXPOSED AGGREGATES FINISH

• ROUGH CAST- a wet plastic mix of 3 parts cement, 1 part lim1,6 parts sand and 4 parts of 6mm to 12 mm crushed stone which is thrown onto the wall by means of scoop or trowel is called as rough cast.

• PEBBLE DASH- A 10 mm coat of 1 part cement,1 part lime and 5 parts sand upon which, while it is still soft, is thrown 6mm to 12mm selected crushed stone which has been well washed is called pebble dash

BROOMED FINISHES

BROOM AND STEEL FINISH

TROWELLED FINISH

STAMPED CONCRETE It is the process of adding texture and color to concrete to make it resemble stone, brick, slate, cobblestone and many other products found in nature including wood, fossils, shells and many more.

The installation consists of pressing molds into the concrete while the concrete is still in its plastic state. Color is achieved by using Dry Shakes or Color Hardeners, Powder or Liquid Releases, Integral Colors or Acid Stains. Stamped Concrete may be used on driveways, patios, commercial roads and parking lots and even interior floors.

ROCK SALT FINISHIt is a decorative concrete finish that is characterised by pits or holes in the surface

ROCK SALTRock salt (essentially sodium chloride) is readily available as either 2-mm to 5-mm granules (eg pool salt) or coarse pieces ranging from 7-mm to 20-mm in size

PROCESS•Rock salt finishes are typically produced by placing and finishing the concrete slab to the desired base texture and colour,•uniformly seeding the surface with granular rock salt particles• rolling or trowelling these into the surface so that only the top of the salt is exposed• curing and then washing to remove the rock salt particles leaving pits or holes.

•They can also be imprinted into the surface using special textured rollers or rubber mats

• SPADED AND TROWELED FINISHES—With wet-concrete and ordinarily good form construction a reasonably good surface appearance can be obtained by spading and troweling.

• Troweling, that is troweling without grout wash requires that the concrete be stripped before it has become too hard to be worked.

• MORTAR AND CEMENT FACING—Where a surface finish of fine texture or of some special color or composition is desired the concrete is often faced with a coat of mortar or, sometimes, neat cement paste or grout.

• Mortar facing is laid from 1 to 2 ins. thick, usually 1½-ins., the mortar being a 1-1, 1-2 or 1-3 mixture and of cement and ordinary sand

Stucco finish

• The ordinary concrete surface with a film-like cement covering will not hold plaster or stucco.

• To get proper adhesion the concrete surface must be scrubbed, treated with acid or tooled before the plaster or stucco is applied and this makes an expensive finish since either of the preliminary treatments constitutes a good finish by itself.

• When a coarse grained facing is made of very dry mixtures, it has been made to hold plaster very well on inside work.

• In general plaster and stucco finishes can be classed as uncertain even when the concrete surface has been prepared to take them.

Aggregates

Aggregates come in a variety of colors, sizes, shapes, textures and materials. The type of aggregate chosen affects the final finish of the concrete.

• Size: Aggregates can range from 3- and 6-mm 'pebbles' to large stones placed into the surface of the concrete, often referred to as 'plumbs‘. Public areas generally do not have aggregates larger than about 20 mm.

• Grading: refers to the distribution of particle sizes in a batch of aggregates. Typical concrete mixes have an even distribution of sizes ranging from fine through to coarse to balance the demands for workability, cohesiveness, strength and durability.

• Shape: Flat and elongated aggregates, referred to as misshapen particles reduce workability and may also have an adverse effect on strength. For barefoot applications the use of rounded river gravel instead of a crushed and angular aggregate is recommended.

• Glass aggregates: Glass aggregates provide a translucent appearance to the finish and are available in a wide range of colors.

Water proofing concrete

• Giving 3 alternate coats of alum and soap solutions. 10gms alum in hot water. 30gms soap in hot water (1l). hot alum first and then hot soap. 3 coats 24hrs apart.

• Dense concrete with well proportioned, non-porous aggregates and low water cement ratio (<.54) to have minimum air voids.

• Small increase in cement ratio which also increases workability.