Liquid Rubber for Decorative Concrete Stamps

When it comes to making decorative concrete stamps, liquid rubber is typically the most desired material for the job. Concrete stamps require a level of strength, flexibility and detail that polyurethane can provide. It is the best material for replicating the look of natural materials at a lower cost compared to wood, metal, and plastic stamps.

Because urethane rubbers come in a range of Shore hardnesses, they are utilized in a handful of concrete applications. The rubbers chosen for concrete stamps are typically more rigid, but they also maintain some flexibility and provide great abrasion resistance in comparison to other rubbers like silicone or latex. Urethane’s abrasion resistance makes it long-lasting and reusable, so contractors can use the same stamp in multiple projects.

What Are the Different Types of Concrete Stamps?

Because urethane rubber is extremely versatile, various types of concrete stamps exist. The main types made with these materials are rigid or semi-rigid mats and flexible texture skins. A combination of these tools is recommended for most projects. They can be used in various indoor and outdoor environments, including courtyards, gardens, pool decks, driveways, sidewalks, entryways, patios, and more.

Rigid and Semi-Rigid Mats

These are the strongest and most durable of all concrete stamping tools. Since they are used for the bulk of the stamping project, they are a bit on the larger side to cover more ground. For contractors to be able to lift them, they will typically have handles molded in to help move them and continue the pattern in the concrete.

Most concrete mats need high strength and structure, so a higher durometer rubber is recommended. When they have higher rigidity, they are better able to leave a detailed impression on the concrete. They produce realistic brick, stone, slate, tile, and wood textures. Each stamp has a unique pattern variation to provide a more authentic look. They will typically have grout lines that can be further indented with special tools.

The rubbers VFI generally recommends for the job are VFI-2180 80 A TDI Molding Rubber and VFI-3180 80 A MDI Fast Molding Rubber. These are firm materials that are good for making these mats. At 80 A, they offer the necessary durability to allow contractors to stand on them during the stamping process.

MDI-based materials work best in controlled, high-production environments where little moisture is involved. The cost and processing abilities of these rubbers are typically most desirable for making stamps. They process better at colder temperatures and cure faster than some TDI rubbers. On the other hand, TDI rubbers offer lower moisture sensitivity, lower exothermic reaction, and extended pot life.

Flexible Texture Skins

Compared to stamping mats, texture skins are much thinner. Their thinner quality makes them lighter and easier to move around on the worksite. They are usually made with feathered edges so they can be rotated or overlapped. They will not have simulated grout lines or joints like rigid mats. This means they don’t need to be aligned in a specific pattern, creating a seamless appearance on the concrete.

The rubber material used for these skins usually feels softer because they are poured thinner for more flexibility on curves, sloped areas, hard-to-reach spots, and vertical surfaces. For increased flexibility, VFI-2190 90 A TDI Fast Molding Rubber is a good choice and also provides great detail.

Specialty Tools

Other tools urethane rubber can be used to make for concrete stamping projects include:

• Medallions are not the most used stamp, but they can elevate a concrete project. They add a more sophisticated, unique touch. A lot of the time, these stamps are custom-made to fit an aesthetic desired by the customer. They will then blend with other rigid mats or texture skin patterns. Examples include compass roses, sunburst designs, Celtic knots, and more. Because urethane rubber is so pliable, it can replicate any original design.
• Texture rollers are also stamping tools that make it easier to imprint a consistent pattern on concrete. Since the pattern is attached to a long handle, contractors can cover more ground quickly. A tamper is not used to press the pattern into the concrete, so the detail won’t be as prominent with this method. This tool is better in applications where detail isn’t as critical, like corners and borders. VFI-3180 and VFI-2190 can be used to make these tools since a harder rubber will help the pattern imprint better detail.
• Edge liners can be used around the borders and vertical surfaces of countertops, fire pits, stairs, benches, etc., to easily imprint textures, patterns, and profiles for an extra touch on stamping projects.
• Stamped concrete can also be used with other decorative concrete elements, such as cast stone and manufactured stone. Urethane rubber molds are used, but they will be lower in durometer than urethane stamps. Check out VFI’s TDI specification sheet for more information.

How Are Concrete Rubber Stamps Made?

Stamped concrete looks realistic because a natural material, like flagstone, ashlar slate, or ceramic tile, is used as a model when making the stamp. 2-part urethane rubber conforms to the details and shape of the original pattern, so there are limitless options for the types of patterns and textures you can replicate. If a large stamp needs to be made, multiple pieces are assembled, and clay is placed between gaps to act as grout lines.

Since the model materials are naturally porous, they must be sealed before the rubber is poured. VFI recommends an 80% to 20% combination of mineral spirits and petroleum jelly by volume. After a few layers of the sealer are applied, a mold release should be used on the models and any surface the rubber will come into contact with.

Some urethane rubber users will pigment the rubber for color coding purposes. Color coding can help contractors differentiate between patterns during the stamping process to prevent unwanted repetition. A urethane pigment is added before the rubber components are combined.

All urethane rubbers come with exact mix ratios by weight and volume so they can properly cure. Once the rubber is measured and mixed thoroughly, it is poured into the form to create the stamp. Depending on the size of the stamp and the needed strength, most rubbers can be poured to 3/8 of an inch thick. If a softer rubber is used, it should be poured thicker (about ½ of an inch thick).

VFI’s MDI rubbers offer shorter pot lives and demold times than some TDI rubbers. This is a great feature if you’re making multiple concrete stamps for one project. Since concrete stamps typically aren’t too large due to weight restrictions, you should have plenty of time to mix up and pour the rubber before it starts to cure. The cure time for VFI’s materials is 4 hours, so the stamp can be demolded on the same day for increased production.

How Long to Let Concrete Set Before Stamping?

The concrete should be firm enough to allow contractors to walk on it before they begin stamping. However, it also needs to be a bit soft to allow the stamp to leave a detailed impression. The more rigid the stamp, the sooner you can start stamping. It’s important to work quickly; otherwise, you might end up with a lighter texture as the concrete hardens.

How long do rubber stamps last?

If the urethane stamp is properly cared for, it can last for multiple jobs. The best part is that they are incredibly easy to maintain. After a stamping project, they can be cleaned with soapy water and a brush or a pressure washer.

Concrete stamp mats should be stored flat. If they need to be stacked, they should be stacked square on top of each other to prevent warping or bending over time. If possible, it’s better if a set of stamps has its own pile. Do not bend or roll them. Store them in a temperature-controlled environment away from direct sunlight. If you store them outdoors, the sun may cause them to deteriorate or chalk.

Contact VFI if you have additional questions about concrete stamping materials or are interested in other molding rubber options.