8 Types of Precast Concrete Finishes

Precast concrete, one of the most prevalent building materials, is used to construct everything from fences, walls, and gates. It can be used outdoors and indoors, making it one of the most versatile concrete types available.

Precast concrete offers several benefits to construction projects. Not only is it extremely adaptable and robust, but it is also simple to maintain and available in a variety of finishes. This is informed by the fact that clients want structurally sound buildings with finishes that set them apart. Some of the most common finishes include:

1. Shot-blasted

The shot-blasted finish is achieved by blasting the product’s surface with extremely small steel shot or recycled glass pieces, which breaks the product’s smooth top surface and provides a rough, textured finish. Typically, this approach exposes the stone or aggregate material inside the concrete mixture, resulting in a unique design element.

One of the main advantages of selecting a shot-blasted finish is the flexibility to choose between light, medium, and heavy blasting. Light blasting reveals very little of the smooth surface, while heavy blasting creates the most textured surface and reveals a great deal of the stone aggregate detail. 

2. Polished Finish 

To add shine to a precast concrete product, a polished finish offers the best results. This is obtained by placing an additive, like resin or varnish, to a honed product, which lends a transparent, shiny coating to the concrete, adding to its visual appeal.

Due to the requirements associated with blasting, honing, and polishing the concrete product, this finish is the most expensive and time-consuming. However, the outcome is more than worth the effort!

3. Off-mold Finish

An off-mold or off-form finish is obtained when a precast concrete object is removed from the mold in which it was cast. This is often quite smooth to the touch as no further treatments are used. Due to air bubbles in the concrete mixture, there may be a few small, visible pockmarks. The off-mold finish is a cost-effective choice that does not sacrifice the aesthetic appeal of a precast concrete product. 

4. Honed Finish  

A honed finish is employed in applications that demand a smooth, uniform concrete surface as well as the visual appeal of an exposed aggregate finish. To obtain a honed concrete finish, a precast concrete component is first shot-blasted to peel away the top layer and then further ground with a grinding disc to create a smooth surface. As a result of the additional labour, honed items are more expensive and have longer manufacturing lead times than off-mold or shot-blasted products.

5. Buffed Finish

A buffed finish is less common than some of the previously listed precast concrete finishes. However, it is not any less enticing to buyers seeking a genuine concrete look. The phrase buffing refers to the application of a polishing compound to an off-mold concrete surface, providing additional protection and giving the concrete a beautiful sheen.

6. Abrasive Blasted

Abrasive blasting removes the form-finished surface using abrasive particles (often sand) propelled by high-velocity air. The blast erodes paste and fine and coarse aggregate. The pace of coarse aggregate deterioration relies on the aggregate’s hardness and the blasting substance. The most often used substance is silica sand. 

Due to the strict EPA and OSHA standards for containment and safety, this option has become prohibitive. Other abrasive blasting ingredients include “Black Beauty” and crushed walnut shells. Protective clothes, boots, gloves, and a hood with a breathing line must be used to prevent inhalation of small silica particles.

7. Exposed Aggregate

A chemical retardant coating must be applied to the precast mold to expose aggregate from within the precast panel. As concrete interacts with the chemical coating, cement retardation occurs, preventing the thin layer of cement from setting. After the panel has hardened and removed from the mold, the retarded cement matrix is rinsed away to expose the aggregate bonded inside the concrete. In retarder-exposed aggregate concrete, irregular aggregate placement and varied depth of exposure, as a result of the chemical reaction, are normal occurrences.

8. Acid-etched Finish

Acid etching is a technique for removing laitance from the surface of the concrete to reveal the colour and texture of the matrix below. Either diluted or gel-form hydrochloric acid is used. The dilution determines the depth of exposure and the duration it remains in contact with concrete before being washed away. 

It may be necessary to repeat the procedure to create a deeper etching. When performing acid etching on vertical surfaces, the personnel should be extra careful to avoid streaking. Usually, one should do the etching three or four days after casting, when the concrete has attained adequate strength but is still permeable to acid. After etching, it may be essential to repair tiny blow-holes that result after eliminating the laitance.

Whether your project involves precast concrete or an on-site pour, hire a reputable and experienced contractor with a wide range of skills and experience. A reputable precast concrete manufacturer like TKL Group will recommend the best finish for your project. Their experience with precast concrete projects is backed by breathtaking architectural masterpieces that feature some of the best finishes around.

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