Concrete being an extremely flexible medium, one can create many varieties of textured edges and surfaces. In this howto I will describe how to create a counter top with edge surfaces having a natural stone look and feel.

The technique used imprinted clay on the edge surface of the form to create the natural stone look.

To begin this process I first made a small test piece to test the method and also to gain experience valuable to creating the finished piece. This is often a good idea especially if you are trying a particular technique for the first time. I experimented with the four sides of the form with different rocks, imprinting styles, and patterns. After pouring the piece I waited until the next to see the results.

With the best experimental method chosen I set about building the form. For the smoothest surface I use melamine coated MDF particle board for the form. Pouring the piece "upside-down" meaning the bottom of the form will shape the top of the counter top. After carefully cutting the boards I drill pilot holes for the screws and assemble the form.

The next VERY IMPORTANT step is to caulk all the seams of the form well. Follow the caulking by wiping so that only the crack has caulk in it and the form surfaces remain clean. This will insure no unwanted impressions in the final product. This step is crucial because if water leaks out the form after pouring bad spots will be created in the concrete because the water carries the portland away with it. Also strength of the piece will be reduced. I generally wait now 24 hours for the caulk to dry.

Created the Textured Edge

I chose regular potter's clay that I obtained from Hobby Lobby. A 25 pound box will be enough for a large piece. Depending on the depth of the impressions you desire choose the thickness of the clay to apply to the form sides. I choose about an inch on this piece. I also varied the thickness of the clay some along the edge to add natural variety. Find a rock from the road, a landscape rock yard, or anywhere to use as the texturing implement. I chose a piece of small culture stone from Home Depot. Using a rubber mallet I gently tapped the rock into the clay. Several rocks were used attempting to create a "random" natural look.

To prevent the concrete and clay mixing during pouring and for easy clay removal some non water soluble substance must be used. I brushed and fingered on olive oil for this piece.



After that experience i might recommend trying Vaseline. Olive oil, being a clean light oil, was used so the residual stain on the concrete would be minimal. Olive oil is also runny which caused me to continually wipe the surface of the melamine. Oil left on the surface of the melamine will show up concrete. The oil on the clay is o.k because the color will be consistent across the edge surface.

Mixing and Pouring

The single most important part of the process is the proper mixing of the concrete. I used Maximizer concrete mix and a powdered charcoal dye. The dry concrete and dye should be mixed thoroughly before adding any water. It is best to mix only one batch of concrete for a single piece to insure consistent color. Add water is small amounts until JUST ENOUGH water is in the mix to make it consistently wet. It should be the consistency of oatmeal. Done correctly the concrete will be wet enough to fill the form evenly and vibrate into one piece but with little to no water rising to the surface. I usually just slap the concrete with my hand and use a rubber mallet tapped to the bottom and sides of the forms to vibrate the concrete. This helps air bubbles escape to insure little to no pits in the finished surface.

When the piece has set long enough in the shade to be firm enough to cover with a tarp do so. This lets the concrete set slowly because remember only the minimum amount of water necessary should be used. By the next day or so you should be able to remove the forms and clay and see a counter top with a natural rock texture finished edge and a smooth top surface.

Finishing

After the piece cures for several days you can sand the piece. This step is optional because the melamine form board creates a very smooth surface. To keep the even color I recommend only using a 220 grit or even 400 grit sandpaper on a random orbital sander. If you sand too much you will start to expose sand, aggregate, and possibly small pits caused air bubbles.

After sanding its best to seal the piece with a penetrating masonry sealer. This may be considered a minimalistic seal. Many other choices of finishing stains, sealers, and engravings are available.

The finishing procedure for the piece in this howto was as follows:

1. Light orbital sanding with 120-grit then 200-grit sandpaper.

2.Spray off the piece with high pressure water

3.Let dry completely....I mean completely....
3a. DO NOT TOUCH IT WITH YOUR FINGERS!!!
If you want perfection then realize the fingers leave behind oils wherever they go and these oils can cause unwanted variation by staining the concrete, creating a area where the stain won't penetrate to the surface of the concrete (oil repels water and acid stain is water based).

4.I used a 100% siliconized acrylic concrete stain coal black in color mixed and purchased at Home Depot. The weather was perfect for painting/staining (overcast,80 degrees, some humidity). I applied only one coat but I basically never let it dry until I had but on the equivalent of 3 coats.

This produced one thick coat applied over about 1-1.5 hours. I poured the acrylic stain on the piece and used a standard painting roller to smooth it over the complete surface and continued to roll back and forth for approximately 30 minutes. The stain will begin to adhere to the entire surface with a continuous film. The small bubbles will disappear and be unnoticeable. This actually stains the concrete, drys within 30-45 minutes, and provides a consistent color with much less variation than acid stain. So if your customer wants a consistent color go with this stain. If the customer likes a varied, unique look go with the acid stain.

5.I let the stain dry for about 18 hours. I believe 6 to 8 is all that's really necessary but I just left it overnight. That next afternoon I applied a Urethane based concrete sealer that I had used to seal slate tile with grout. It had worked great then. The sealer was a high gloss. I used a small plastic squirt bottle to spray the sealer on the concrete and used a roller to spread it around evenly.
Withing 4 hours the piece was dry and ready to use

6. Installed the pieces into the kitchen.