Modello Options Overview
Modellos can be used for a wide variety of custom and artistic techniques on concrete surfaces, including
- Acid Etching/Color Removal
- Positive Color Application
- Color Resists
- Embossed (raised) and Inlaid (recessed) Images
For most applications, other than sandblasting and heavily embossed designs, 4 mil white vinyl will be the material of choice on smooth concrete surfaces.
4 mil white vinyl will NOT bond well, however to concrete surfaces containing an aggregate or with a textured “broomed” finish. In that case 10 or 25 mil vinyl may work. "Test" sample are provide upon request
For light sandblasting, 10 mil is recommended. Deeper carving will require 25 mil green rubber. These thicker materials will not accommodate small, intricate designs.
Acid Etching/Color Removal
This process involves first acid staining the background area with the desired color. After the acid stain has been neutralized and is completely dry, the Modello pattern is applied and a gel-based acid etching crème is applied to remove the color/stain from the concrete surface in the exposed areas-similar to the effects of bleach on blue jeans. Gelled Acid Recipe: for stronger acid mix 1 part Muriatic Acid with 2 parts Gel-lo. For a less agressive gelled acid, dilute the acid first with water (1:1 or your desired ratio) before blending that mixture with 2 parts Gel-lo.
The design shown is a border with a negative weed (meaning the background area or negative space surrounding the design has been removed.
The etching gel will react differently on different types of concrete surfaces. Concrete slabs that contain a larger amount of lime will experience an actual etching of the surface, creating a slightly rougher texture in the etched areas. The acrylic polymers present in cementitious overlayments will result in a simple color removal only. The longer the DesignEtch remains on the surface, the more “bleaching” will occur.
Positive Color Application
Modellos can be used for Positive Color Application on concrete, but special care and consideration must be taken in the application because Modellos will NOT prevent liquid acid stains or dyes from seeping or “wicking” outside the design areas.
There are three basic ways to apply color/stain cleanly and effectively with Modellos:
Utilize a thickening agent such as Modello Gel-lo to brush on the stain.
Spray solvent or water-based dyes using a Preval sprayer.
Stencil, sponge or paint on color, such as Modello Dye Stains in their concentrated form.
Modello Gel-lo, a thickening additive, can be added to acid stains or water-based dyes to create a color/gel that can be brushed or troweled over the exposed Modello areas to stain them. It serves to provide more color control and to reduce or prevent "wicking" or seepage of the liquid stain under and around the edges of the Modello pattern.
Sprayed Stains or Dyes
Preval sprayers are available in the paint department of your local home hardware store (Home Depot, Lowes). They consist of a glass jar onto which a Co2 canister is screwed on, which acts as a propellant. The stain or dye can be diluted and placed in the jar for easy spraying through a Modello. The spray needs to be applied in thin, light layers (allow to dry between layers) to build up depth of color. A heavy, wet application will result in bleed-through or “wicking” under the Modello pattern.
In addition to Modellos, traditional mylar stencils can be used in conjunction with Modello Dye Stains and stencil brushes to create a wide range of interesting effects. Modello Dye Stains are water-based stains in a concentrated form, making they ideal for stenciling on concrete (as well as a multitude of other surfaces).
Modello Dye Stains are available in 24 designer colors and three different series: Essential Colors, Vibrant Colors and Metallic Colors.
Modellos can be used to create resist patterns in a number of ways. Of course, Negative Weed Modellos can be used and etched, embossed or sprayed around. The focus here though is how to use a Positive Weed pattern to create a resist.
To create a “resist” pattern, a solvent-based sealer or water-based sealers can be sprayed or brushed through the pattern openings.
The solvent sealer needs to be sprayed on thinly and in layers as a very heavy application may cause the Acetone to “eat” the vinyl-not a usual occurance but beware.
After the concrete in the design area has been sealed, the Modello is removed and the unsealed areas (negative spaces around the design) can be stained with an acid-based stain. The sealed areas will “resist” the stain and will remain unaffected.
This technique can also be combined with a “Positive Color Application” technique. In that case the colors/stains can be sprayed through the Modello to create a colored design or image and then sealed with the solvent sealer prior to the Modello removal.
Embossing concrete means troweling or spraying a cementitious overlayment (such as Colormaker’s Sgraffino, Skimstone or Concrete Solutions Sray Top) through a Modello pattern to create a raised image.
The same issues are true for embossing with concrete as with any other textural medium:
Care should be take not to emboss too heavily, so as to “bury” the design. It will be difficult to find the Modello pattern for removal if the overlayment is trowelled on too heavily. Apply only just past the thickness of the Modello
To get a clean image, the overlayment should be allowed to dry completely (can be overnight). If the material is in a half dry/half wet state when the Modello pattern is pulled the edges of the design may appear “ragged”.
There are many variations for embossing, including
- Emboss with the same color/material as background and stain all at the same time.
- Stain the background, let dry, emboss, pull Modello and then restain with a lighter (or darker) color.
- Stain the background, let dry, emboss and color the raised design with the Modello still in place to create a high contrast and completely different color treatment.
Modellos can be used for sandblasting patterns into concrete slabs. For light surface etching, the 10 mil green rubber is appropriate.
For deeper carving 25 mil green rubber should be used. We can also special order a 42 mil rubber material for even deeper carving. We do NOT stock this material currently, however, and would need 1-2 weeks lead time for ordering.
All of these decorative options are detailed out in the various techniques presented here on the website and are intended to provide additional instruction and inspiration for those already familiar and working with concrete.
If you are new to decorative concrete, we highly recommend that you attend a workshop (See our Workshop and Resource Links pages) for specific and hands-on instruction in the concrete medium.