What is Stamped Concrete? – Its Features and Its Construction

The Stamped concrete can be defined as a finish that is provided to the concrete in its wet state. Specific designs or patterns are stamped on the concrete in its plastic state as shown in the figure-1 below.

Fig.1. Stamped Concrete Preparation on a Concrete Driveway

The stamped concrete provides a great option in terms of realistic colors, textures, and patterns. These will hence end up with a final product finish similar to that obtained from the installation of granite, marble or costlier sandstones or tiles. Thus, stamped concrete provides great option for the designers to choose a design for the floor for various budget and aesthetics.

A greater advancement in the area of stamped concrete have resulted in the development of new patterns similar to the stone patterns. 

Fig.2. Stamped Concrete Finish similar to Stone Patterns

The use of stamped concrete will help in achieving the appearance of an imported stone for a lower cost.

Stamped Concrete Construction 

A teresting texture is provided by the application of stamped finish for the sidewalks, patios, and driveways. The main design element for the process is stamping mats. The figure-3 below shows some of the rubber - stamping mats that are available. There are numerous designs of stamping mats in the market.

Fig.3: Stamping Rubber Mats with Hexagonal, brick and square patterns

Along with the decision of implementing stamped concrete, it is very necessary to bring a decision on the layout of stamping and the type of stamping pattern that will suit your floor. This will help in maintaining a consistent pattern throughout the course of the project. 

To maintain a consistent layout, a reference line is made during the stamping of the initial stamping mat. Further stamping can be carried out with respect to the initial reference line hence achieving proper alignment and consistency. Each stamping mat will be aligned with the before stamped layout. This method is followed till the end of the project. 

The textures at the corners of the stamped portion mostly have to be finished by hand. Necessary obstructions can be created on the surface with the help of special stamps or by using an aluminum chisel. 

The stamping pads is pressed with pressure over a concrete surface that is in its plastic state (slightly stiff) to a depth of 1 inch. 

Stamping a Concrete Surface

The process of stamping a concrete surface can be conducted by the following step by step procedure.

Step 1: To a prepared formwork, the concrete of required mix ratio is poured and leveled to form a concrete slab. A reference line is made at the point where the first mat is intended to be placed or at the center of the form. The time we observe that the bleeding water has disappeared from the surface of the slab, a release agent in the form of powder is tossed on its surface. The amount to be tossed is dependent on the instructions given by the manufacturer. The procedure is shown in the figure-4.

Fig.4: Preparation of Concrete Surface for Stamping

Step 2: Next is the process of aligning the stamping mat of desired pattern over the prepared concrete surface as shown in the figure-5.

Fig.5: The first Stamping of the concrete Surface

The stamping mat is aligned with respect to the reference line made and based on the layout plan. It is to be noted that once the mat is placed, no kind of adjustment have to be conducted. The mat can be pressured and embedded into the concrete either by stepping over it or by tamping with hand.

Step 3: Now the second stamp is taken and placed against the first as shown in figure-6. And if there are many stamps of the same pattern, it can be embedded in the continuous pattern. If only one mat is available, after each stamping, the mat have to be removed and continue the stamping.

Fig.6: Placement of Second pad for stamping the concrete

If we have to reuse the mat after each stamping, then it is suggested to complete row-wise first before finishing lengthwise.

Step 4: Once the stamping procedure is over, the surface is cured for 3 days. The releasing agent that is used can be removed with the help of pressure washer. Then a complete curing can be performed for the concrete surface for a time period of 1 week. Finally, as per the manufactures, an acrylic concrete sealer can be provided. After which the formworks and the backfills can be removed, as shown in figure-7.

Fig.7: Finishing the Stamped Concrete with a Concrete Sealer

Based on the aesthetic views of the worker or as desired, more and more detailing works can be performed on the stamped concrete with a roller to defined each block, or texture skin that will provide the look of a natural tile or a stone. Most of the professional stamping pads with give complete finish for the concrete surface. 

Tips while Stamping Concrete

Some essential tips can be followed before you work with a new stamping pad or if you are new in stamping concrete.

• Before working on concrete, we can apply the pads on a bed of compacted sand.
• Always try to bring random designs. Avoid placing the stamping pads in a repetitive pattern. 
• Better results will be obtained if we use a releasing agent. This will help to avoid any kind of breakage of concrete while taking out the stamping pads.
• Check the alignment of the stamping pad periodically.
• The person who is working over the concrete surface, performing the stamping procedure must wear a boot or work shoes that is clean. It must be free from debris, pebbles or other dirt. Or else these contaminants will also be impressed over the concrete surface. 

What is Efflorescence? Causes, Prevention and Removal Techniques

The brick masonry industry is plagued with a stubborn and persistent confusing delinquent trouble frequently seen as white powdery scum on a lot of buildings. This white powdery substance is termed as efflorescence which is, although, not well understood but still the masonry industry is still able to define it, knows where it comes from and also methods to reduce and prevent this badly-behaved nature in brick masonry have been device and practiced these days.  

Sure Ways to Prevent and Cure Efflorescence

According to dictionaries the efflorescence is defined as:- 

A change on the surface to a powdery substance upon exposure to air, as a crystalline substance through loss of water.

To become encrusted or covered with crystals of salt or the like through evaporation or chemical change.

Actually efflorescence is a deposit of water-soluble salts that are left on the surface of masonry as a crystalline powder sometimes white or brown or green or yellow after the water evaporates from the exterior surfaces upon exposure. You might have not seen any color other than white but still it exists depending on the type of salts etc. 

This is a prominent defect in brick masonry. In moist climate, in damp places, like basements or under leaky gutter, masonry often gets disfigured. Deposit originates from the mortar and frequently spreads over a part or entire face of the wall. 

Absorbed water dissolves the salts of sodium, potassium and evaporating, forms a crystalline deposit on the surface. In addition to unsightly appearance, the crystallization of salts in the pores of the bricks or mortar may cause disruptive expansion resulting in disintegration due to cracking. 

The problem of efflorescence is not new; its existence finds its way back in the prehistoric primitive times as the brick masonry was ever started and great piece of time, money and efforts have been made and spent trying to solve the difficulties generated by this persevering problem.  

The timing of when the efflorescence appears is very critical, it open appears just after the completion of the structure and is thus named as “new building bloom”.  And at this time the contractor, builder or architect are mostly concerned with the appearance of the new structure. The appearance of efflorescence is triggered by variation of temperature and is obvious during the winter, but may also be observed throughout the year following heavy rains and sudden drops in temperature.  In summer, even after prolonged periods of rain, moisture evaporates so quickly that only small amounts of salt are transported to the surface. However, during winter, slower rates of evaporation lead to migration of salts to the surface. 

This article will explain in detail about the sources of the efflorescence, how it works, about the attempts that are to be made in order to reduce its destructive effects and if it does appear the ways to remove it.

Sources and Causes of Efflorescence  

In most general cases, the efflorescence is caused when the water gets mixed with masonry material and thus moving the salts to the surface and usually the free salts were created. In other cases when the free salts are readily available the free water dilutes it into a solution which is transported through brick masonry depositing it on the surface referred as efflorescence. 

During detailed analysis of the efflorescence it was found that sometimes the salts which are deposited inside the brick masonry form a crystal depositing within the matrix of masonry called crytoflorescenc as it is not visible. 

Conditions for Efflorescence 

The subject of efflorescence is not that simple, it is a confusing mechanism and the real cause is hard to find sometimes. However, it is well known that there are three conditions that must be met in order for the efflorescence to appear. 

• First: There must be water-soluble salts present somewhere in the wall
• Second: There must be sufficient moisture in the wall to render the salts into a solution
• Third: there must be a path for the soluble salts to migrate through to the surface where the moisture can evaporate, thus depositing the salts which can crystallize and cause efflorescence. 

These three conditions must be simultaneously existed in any structure for the appearance of the efflorescence which means if any one of the cases does not exists than no efflorescence will appear. 

Although the efflorescence is a complex problem, the prevention is not that difficult with economic and feasible steps there exists ways to reduce any one of the cases/conditions required and is thus making nearly impossible for efflorescence to occur. 

Sources of Salts 

The chemical reason and nature of efflorescence is very complex as there are many chemicals in the clay bricks, concrete blocks, mortar used, cement, lime, sand, admixture and ground water that can cause sulfates, carbonates, sodium bicarbonate or silicate to cause efflorescence. The efflorescence in green color which is often termed as “Green Stain” is a result of certain vanadium and molybdenum compounds present in some ceramic brick units. Similarly in brown color the efflorescence called “Brown stain” exists which is due to manganese deposits. 

 The appearance of efflorescence is generally not dependent on the quantity present of the water soluble salts as it is reported that even very small quantities of water soluble salts causes efflorescence.  Sodium and potassium hydroxides are commonly present in Portland cements which may cause some efflorescence during the first year after construction. This is known as “Building-bloom”, a condition which typically disappears after a short while. 

Moisture 

If your house/building you are constructing is in areas of high annual rainfall than it must be considered in the initial stages and planning of project that the materials will be subjected to higher quantities of water both during and after construction making it more susceptible and liable for efflorescence. Similarly even if the rainfall is not more, the area is near sea where humidity is always more than in such areas the projects are also greater exposed for efflorescence potential. 

As water is always needed for the salt to dissolve, which means if more water exists the more solution will be prepared and thus more salt will dissolve causing more efflorescence. 

So after discussing sources and reasons of efflorescence we can conclude that detailed study of the following items is necessary for judging the reason and prevention measures for the efflorescence :- 

1. Moisture 

2. Construction Material

3. Temperature

Preventive and Controlling measures 

Since many factors influence the formation of efflorescence, it is difficult to predict if and when any will appear: There is no accepted standard test method for   reassuring the efflorescence potential of masonry mortar. Several experimental methods have been proposed, but none has been accepted as effectively predicting the performance of mortar materials in actual use.

After finding the reasons and causes of the efflorescence it will be easy for the one to control it prior to avoid the situation to get worsen. Even if the soluble alkali sulfates exist in a masonry wall, before the sulfates can cause efflorescence the salts must be dissolved into solution by water. If no moisture reaches the sulfates than they cannot be rendered into solution and migrate to the surface where the water will evaporate, leaving the sulfates salts on the surface to crystallize and become efflorescence. Attention must be given to preventing any soluble alkaline sulfates from being rendered into solution by water. 

This is difficult since during construction water is naturally used in the mortar and grout; therefore the amount of water in the wall should be controlled to only reduce the amount necessary for actual construction. The majority of the water is absorbed into the masonry and used to chemically react with the Portland cement and hydrated   me and is thus not free water.

To avoid Efflorescence do not use porous bricks in contact with limestone. Protect brickwork against contamination of salt-bearing materials during building operations. Bricks should be thoroughly soaked during construction. Correct design of DPC should be used.

Once the cause of efflorescence is corrected, the removal of the deposit is relatively easy, since most efflorescing salts are water soluble. In general, efflorescence can be removed by dry-brushing followed by flushing with clean water. If this is not satisfactory, walls can be washed with a five to ten percent solution of muriatic acid. It is always advisable that a small inconspicuous test area be tried first to determine whether etching or other discoloring will occur. After the acid treatment, the surface should be immediately and thoroughly flushed with clean water.

To summarize, three conditions must exist before efflorescence can occur. If these three conditions can be controlled, there should be no efflorescing of masonry walls.

1. Reduce all soluble alkali sulfates.

2. Use good details to prevent water from entering the masonry.

3. Use good construction practices to eliminate migratory paths for moisture.

Remember, it is very difficult to totally control any one of these three conditions, but it is relatively simple to reduce the effect each one has towards efflorescence. The following 5 simple ways are a sure way towards efflorescence free brick / block masonry for your project. 

1. Limit Driving Moisture Force

2. Provide for good drainage

3. Construct good mortar joints

4. Ensure proper curing

5. Limit Water Entry