Making Impressions in Concrete

by Jeff Potvin, The Concrete Network

Brad Bowman developed the process known as stamped concrete in the mid 1950's. With advancements in tool texture and release agents the art of texturing concrete was born. Today, the market is filled with different forms of stamping tools that include some shapes that manufacturers universally use. I'm writing on what I have learned on using some of these shapes.

The first trick to laying out stamping tools is having enough of them. The number of tools needed depends on how a particular pattern lays out. The rule of thumb is to have enough tools to span the widest point one and a half times: the reason for this is that you should always try to stamp tools while they are locked together. If they are not locked together, the stamping tools can move.

If you don't have enough stamp tools, break up the pour with bands, cold joints or expansion joints. While thinking of the stamp pattern layout, also decide where to begin and end the stamping pattern. While looking at this, keep in mind the amount of hand stamping, tracking, and how the pattern will reconnect, especial on pool decks. Pool decks are a little tricky, since you need to go around the pool and have the pattern reconnect. I usually pick the narrowest point of the pool deck for this connection, which helps hide any alignment problems.

The first shape shown below in Figure A is the fan or fish tail pattern. This shape should always open up towards the focal point, such as a front door or entrance. This shape is hard to hand stamp and alignment with a previous poured area can be difficult. Using bands as an edge detail will make both of these problems easy to deal with. The fan will have a tendency of curving or meandering while stamping. To help keep the tools straight apply a line of powdered release ahead of the tools and lightly snap a string line in it. Using a corner of the tool as a reference follow the line, this will keep the pattern running straight. Also, a line will help in cases where there are not any straight edges to follow.

Figure A- the fan or fish tail pattern

The notched shape shown in figure B was designed to reduce the number of straight lines in the slate patterns. With this shape you need to be careful because it will track. Tracking is when you can identify a repetition of lines. Some patterns only show the tracking when you look at them in a certain direction. That's why you want the focal point of the pattern to be pointed in the right direction. While setting this pattern I use the notch as an arrow and keep it pointed in the same direction eliminating any confusion while setting the tools.

Figure B- Notched Ashlar Pattern

There are a couple different configurations of the running bond shape shown in figure C below. One uses a fingered type connection and the other is a stair step. The stair step has a tendency of not staying straight. Overlapping the tools half way will help this issue. But take a look at the short bond grout lines on the tools and make sure that they don't line up. When coming to an edge with this shape, I measure a couple rows out to make sure that I will land even. If the tools are crooked I cheat the ends of the last few rows to straighten it out.

Figure C- Running Bond Pattern

The seamless texture skin shown in figure D was designed to cover a large area at one time. This allows contractors to place and stamp more square footage in a day. One particular tool has a heavy ridge that runs through the pattern. If the tools are turned wrong it will make circles in the slab. Note the arrows in the figure D below, each time the tool is moved you should turn it 90°. I like to mark the back of the tool so that I can identify the direction that the tool is running. When stamping skins you should overlap them 6" to 1'. Before moving the skin the overlap needs to be reversed and re-stamped along the edge of the exposed side.

Figure D-Seamless Texture skin

When making an impression in concrete you need a little preparation to prevent mistakes. Each stamp tool shape has a technique that makes the installation go smoother. The concrete is not going to wait for you to figure it out. I have trained some contractors on a bed of damp sand, so that the mistakes can be raked out. You should hide tracking and eliminate hand stamping whenever possible. Make sure that you start with enough tools and a plan of attack for the job.

Jeff Potvin

Jeff Potvin, a Civil Engineer and the owner of Architectural Concrete Consultants, has nearly fifteen years of experience in the architectural concrete industry. Hisexperienceincludes stamped concrete, overlays, form-liners, acid stains, counter tops and coatings.

He helps contractors get started in the industry with hands on training, promoting, product selection and troubleshooting. Property owners such as theme parks and retailstoresconsult with him on product sourcing and maintenance issues. Architects and Engineers utilize Jeff's knowledge on the preparation of specifications and oneducationalpresentations. He is a member of ASCE, ACI, ASCC, IAAPA and the DCC.

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