Creative Concrete Stamping
Stamping concrete is an affordable way to imitate the look of natural stone or brick without having to pay for the real thing. Proprietary rubber patterns that create effects resembling natural stone, and preconfigured patterns such as brick or cobblestone, are commercially available, but sometimes look like what they are — artificial.
One alternative is to create your own stamping patterns. My stamp impressions are full of variety and often are made from found objects. Used with discretion, a stamp is an effective decorative tool. The concrete can simply be concrete, without trying to imitate something else.
But this is often the case with good design. And though there are no limits to the imaginative combinations of the practical and the aesthetic, applying a philosophy of restraint is a good idea when using stamping techniques to design a floor.
Creative concrete stamping can be done with found objects, such as this Indonesian batik print woodblock used as a design tool. We placed the block and tapped it lightly with a hammer to make the impression.
Commercial stamping produces (and produces and produces) accurate imitations, but I prefer to let concrete speak for itself and tend to use stamps discreetly, in ways that bring out concrete’s natural beauty. These stamps are typically found objects, a batik woodblock or part of an auto transmission, for example. Anything can be used to stamp the concrete as long as it’s durable and doesn’t have a tendency to stick and pull up the finished surface. The way we use these found objects, stamping is pretty simple. We’ll take our stamp, place it on the wet surface of the concrete, and tap on it a few times with a hammer to create a stamped impression.
A commercial stamp is perfect for making basic improvements to a plain slab on grade, like this patio which looks like brickwork.
For a project at Clark Place, a basic slab-on-grade floor and patio in El Cerrito, California, we used a batik woodblock and a short strip of leftover copper. On the patio, we created our own rubber stamp using a found object, in this case a sheet-metal panel from an old ceiling. We incorporated the panel into a 2-inch-deep mold, mixed up a two-part rubber compound, poured it into the mold, and a day later had a beautiful, workable rubber stamp.
Creating your own stamp tool is straight-forward and fun. We used a salvaged 2-by-2-foot square from a tin ceiling for the decorative stamp on the Clark Place patio. The Art Deco–style star design had a shallow relief, so it would read well on concrete. The release agent added a gray-blue hue, which mixed with the moisture in the concrete and accentuated the detail nicely.
Stamping with found objects entails some risk and should be approached in a sense of playfulness. Commercial stamps are designed to consistently pull free from the concrete, leaving behind a clean impression. A found object, such as a batik woodblock or auto transmission part, on the other hand, isn’t intended for this sort of use. There have been times, usually when we’ve tried to stamp when the concrete hasn’t set up sufficiently, that we would get a ragged hole instead of a clean impression when some of the concrete pulled up with the stamp. But it’s easy enough to fill in the hole and try again. And there have been times when we’ve tried to stamp into concrete that’s gotten a bit too hard, and we’ve ended up with no clear impression and a broken stamp. If you’re new to concrete, we recommend making a few small samples and experimenting with stamps, to get a feel for the timing.
A mold was cast from a tin ceiling panel. Thoroughly blend the two-part urethane with a low-speed drill and paddle.
Pour evenly and methodically to prevent voids from trapped air. After a day’s curing, the tough urethane stamp pulls cleanly from the tin mold with release agent.
Commercial stampers, because they make so many impressions, use release agents so that the stamp pulls away cleanly. Some commercial stamps rely on a thin plastic sheet in place of a release agent, which serves the same purpose. Very often, the release agent is colored, and it acts like a color hardener; it’s spread on the wet concrete, then is driven into the cream on the surface as the impression is made. A release agent doesn’t get troweled into the concrete, though, and most of it will wash away unless it’s sealed with some type of topical sealer. We used a release agent with the rubber stamp on the Clark Place patio and left a residue to accentuate the stamp relief.
On the Clark Place patio, a dark blue-gray release agent was spread liberally at the site to be stamped. The stamp is carefully positioned so the release agent is not scattered to the adjacent concrete.
Here, a crew member stands on one edge of the stamp while he tamps the other. It’s important to distribute weight evenly to produce a uniform impression.
The resulting stamped concrete.
Whether you use a found object for a stamp, a homemade stamp, or a commercial stamp, there are a few basic things to consider:
No stamp cuts deeply enough for the pattern to serve in any way as a control joint, so a stamped slab, like any slab, will need joints (joints and stamped designs will need to be integrated). Typically, the control joints can serve as dividing lines between stamped fields, and may demarcate pattern changes. Take into account the width of the control joints when laying out your stamped patterns.
Do your layout before the concrete arrives, so you know exactly where you’ll start and finish; you don’t want to be figuring this out while the concrete is setting up.
The best concrete mix for a stamped floor has 6 to 6.5 sacks of concrete per cubic yard, and 3⁄8-inch pea gravel. Large rock may make it more difficult to stamp to the desired depth/relief.
Tell the batch plant that you intend to stamp the concrete, and find out if retarder or accelerator is recommended for the prevailing weather conditions in your area.
Like inlays, stamping can be created with found objects. This delicate pattern was made with an Indian batik wood stamp and a car spring.
The small stamp, a classic lotus pattern, was pressed about 1⁄8 in. into the concrete.
Adding Some Color
As long as you’re jazzing up a concrete project, you might consider adding a little color to boost its appeal. Uncolored concrete can be pale, gray and boring and even cure to various shades, but adding color at the mixing stage will allow an interesting tint that will permeate throughout the batch, providing a uniform color. In this case, the subsurface concrete will retain its color properties as the top layer erodes over time. However, the drawback of integral powdered pigments for a large batch can carry an expensive price tag.
A color hardener is a fine mix of pigments, cement and conditioning agents that create a hard, colored surface. Also called “dry-shake” hardeners, these products are cast onto the wet concrete and troweled into the creamy surface. Dry skae colorants can achieve a more dramatic, intensely colored concrete than an integral color.
Adding color to existing slabs is more difficult. Depending on the application, four different products can be used: concrete stain, epoxy paint, or latex or oil-based porch and floor paint.
Professional staining is generally the way to go, because it lasts longer than old-fashioned floor paints. Staining the concrete yourself is relatively inexpensive, but keep in mind, staining concrete is not like staining wood. You can’t just pop open the can and start staining. A great deal of preparation is required. If you don’t follow the right procedures, the job can end up a huge mess.
The prep work entails cleaning, an acid bath, rinsing and neutralizing, which can be a lot of work. But if everything goes right, you will have a job that will add beauty to your property for years.
This article is an excerpt from Concrete at Home, a new book by best-selling author Fu-Tung Cheng, a recognized master craftsman of residential concrete design. With his new title, Cheng shows you the anything-is-possible flexibility of concrete, and gives you the step-by-step guidance and confidence to form, pour and polish your own distinctive countertops, floors, walls, fireplaces and more. For more information about Concrete at Home, visit www.taunton.com or call 1-800-477-8727.