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Preparation
The concrete needs to be clean. And not water hose clean. Rent a 3000 PSI or stronger pressure washer. The higher the better. Oil and grease should be removed with a degreaser. There are several out there and if you follow the manufacturers directions they will work. On older stains or oil from diesel there may be a halo which remains after the degreasing. This is normal.
The next step is to take muratic acid and dilute it with water and clean/etch the concrete surface. If the concrete is hard and smooth you may need one gallon acid to 5 gallons water. On rougher surfaces one gallon acid to 10 gallons water will be fine. Remember add acid to water never water to acid! Wash the concrete quickly to remove loose dirt and dampen the concrete. Squeegee any standing water. With a plastic water can spread the acid. Be sure the entire surface has been covered with the diluted acid. It should bubble and fizz. Keep the concrete wet with the acid for 5 to 10 minutes. At the end of that time mix one cup of non-sudsing ammonia with two gallons of water. Depending on the size of the surface you may need more neutralizer. Just keep the ratio of one cup to two gallons. Spread this over the acid washed concrete. This will neutralize the acid. Scrub the ammonia solution in. Then take the pressure washer and wash the bejebbers out of the concrete. If you have any questions about the concrete being clean, wash it again!
If you are going to have a failure with the overlay, poor surface preparation will be the number one reason. So Clean, Clean, Clean.
Squeegee the concrete to remove standing water and get ready to mix your overlay
Mixing
You will need several CLEAN five gallon buckets, a squeegee, trowel, mixer blade and a slow speed electric drill (Milwaukee Hole Hawg recommended) The electric drill will need to be heave duty and slow speed.
As for the overlay material itself, I have used pre-packaged and home rolled formulas. Quickrete makes a product called Concrete Resurfacer. It is becoming available at more Home Depot stores. If they dont have it, ask and they can get it. Another product is Conspec Overcrete. Their kit consist of the bag mix and a jug of Overcrete Copolymer. Conspec is available throughout the United States. Conspec is a good company and have great people and offer a lot of technical assistance. To choose between the two, I would go with Conspec. It has a longer open pot life. Which means when you mix it how long you have before it starts to set and becomes unusable. With any product, if it starts to set, get rid of it and mix a new batch. The Quikrete will start to set in 20 minutes even in a closed bucket. If the temperature is in the high 90s even faster. The Overcrete will remain usable 12 to 24 hours in a closed bucket. The higher the temp the faster the set. On a hot day be sure the liquids are cold. Use ice water for the Quikrete and put the Conspec Copolymer in the refrigerator or ice it down before use. When the temperature drops below 80 this becomes unnecessary.
Add the liquid to a CLEAN five gallon bucket. Add about ½ of the grout mix and begin mixing. If you mix too fast or too long you will put air into the mixture. This will result in bubbles in the finished surface. When the mix becomes smooth add the rest of the grout mix. The consistency you are looking for is between buttermilk and pancake batter. If the Overcrete is too dry add clean water sparingly, an ounce at a time, until the proper consistency is obtained. With the Quikrete, you add water until it reaches the proper consistency. But never more than 8 quarts.
Again, mix just long enough to make the mixture smooth and lump free.
Have a clean bucket of water available to "spin off" your mixer. This gets you ready for the next step.
Placement
These products can be applied by spray, trowel, brush, roller, or squeegee.
The concrete can be damp but there cannot be any standing water.
You can lay out design patterns using fiberglass reinforced strapping tape. Do not use masking tape unless you are putting down a very light coat. It is not strong enough to hold up when you go to pull it up. Then you have problems. Stick with strapping tape. Or if you want pre-designed patterns, Otto Dukes has Faux Tile patterns available in various designs. For a tile pattern, strapping tape is the most cost effective way to lay out a pattern.
I always like to put down a squeegee coat first. This gives the next coat a like material to bond to. The cost of a squeegee coat is minimal compared to the benefits.
A squeegee coat is the consistency of buttermilk. All you are looking for is a thin layer. If you have divots, low areas, chunks missing, these need to be filled before applying the squeegee coat. If not, you will not fill them with the squeegee coat. Dont fool yourself into thinking you can fill it. Go ahead and repair everything first to give you a smooth surface to start with!
The squeegee coat will dry quickly. Even in high humidity conditions it will be ready to take the pattern or the second coat in two hours. When the temperature drops below 70 you may need to wait overnight before the pattern or second coat.
Brushing - Use a stiff bristle wall paper brush. When squeegeeing the first coat, keep one of these handy to get those areas you miss with the squeegee or those ridges you just never get out.
Rolling - Use a drywall texture roller. These have little loops in them that will make the surface non-skid. This is great around swimming pools when repairing Kool-Deck or texturing pool decks.
Spraying - Use a standard drywall hopper gun with and air compressor. Set the air for 15 to 30 PSI. You vary the size of the nozzle to give different splatter effects. The smaller the nozzle the smaller the texture will be. When spraying, hold the gun horizontal to the surface. There are rubber ells available which allow you easier holding of the gun. Two thirds full the hopper gun will weigh 25 to 30 pounds. Make the overlay mix the consistency of pancake batter. Too stiff and it will not spray well. Too thin and it will not stand up if you are doing a "knockdown" design. When spraying, mix each batch separate. When using the Conspec Overcrete you can mix two or three bags of grout without worrying about set. But the Quikrete will set in 20 minutes or less so dont dawdle. If you see hardening of the materials, get rid of them. The chunks will clog the gun and you will loose the hopper of material anyway. I would recommend mixing each batch separate in a CLEAN five gallon bucket. While it may take a little more time it will make up for it in less aggravation. When doing a "knockdown" design, after spraying, let the mix set for five to ten minutes then hit it with the trowel. Have some old golf shoes so you dont schmeer the overlay.
Trowel - Have the mix a little stiffer than for spraying. Dont over trowel. Spread it out then move on. Dont press to hard. The idea is to have a nice level coat. The materials will do the work. If you want a stone texture effect, let the trowel coat dry until you can walk without leaving impression in the surface. Mix up some more material fairly stiff and flick it on the surface. Hit it with the trowel. What you are looking for is an uneven surface. You can do this with several coats to build up the effect. You can also use colored grout to give it different shades. This works great in flagstone designs. Going over these textures with an acid stain will give the appearance of natural stone.
This brings us to the final step.
Curing
These materials are self curing. However in windy dry conditions or areas they may need to have a fine mist of water sprayed on them for 24 hours to keep the surface damp. After 24 hours, let it dry. The surface can take light foot traffic in 4-8 hours and heavy traffic within 24 to 48 hours. If the surface is to be subject to extreme heavy traffic or forklifts, use a heavy duty product or protect the surface with a urethane topcoat.
I have left out sealing.
Sealer will make the overlay last. It will make it easy to clean and maintain. However, when using sealer around wet areas such as swimming pools or entrances, they need to be slip resistant or have a slip resistant additive added to the sealer. Solvent based sealers will darken the color. Water based sealers will not. If the color is what you want, and you do not want it darker, do not use a solvent based sealer. You taint gonna be happy! Water based sealers are harder to work with and there have been problems with the sealer turning white. This is because the sealer traps moisture between the sealer and the surface. There are sealers now available that allow the surface to breathe. While not eliminating the problem they are getting easier to work with.
This is by no means a complete course in concrete overlay. You can take this information and with common sense make a stunning concrete overlay. There are acid stains, dyes and tints you can use to add color. Your imagination can be created. If you have questions call me or check my web site. There are forums on the internet where you can ask questions and get answers. www.decorativeconcrete.net and www.acid-stain.com are the best. Check them out, learn and educate yourself. Make the world a little less gray. And make people say ?! That IS Concrete !?
Disclaimer:
You are responsible for following my advice. You will be using materials and process which you could get exposed to bad and heavy stuff. Follow the manufacturers recommended procedures for their materials. I dont want anyone to get hurt while making the world a more beautiful place. If you feel anything is beyond your experience or ability call for help. I am more than happy to pass on advice to you. But you are responsible.
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