Question: F. Tim, I need to replace a broken section of my concrete driveway. My main concern is that the color and texture of the new patch match the existing driveway as closely as possible. It doesn’t have to be perfect, just close. How do you do it? I read your previous concrete repair columns on askthebuilder.com so that I could understand how the concrete is mixed, placed and finished. What do contractors use to paint the concrete to make it white? – Donn R., Clemson, South Carolina
A. You may be faced with the same puzzle as Donn. Perhaps you are trying to find a stucco stain on the wall. Or maybe you want to fix the grout between bricks in your home.
I’m sure you’ve seen garish repairs where the new patching material stands out like a red wine stain on a white blouse. While it is possible to get up close and personal with such masonry repairs, it is next to impossible to get a perfect match. If you have patience – and many don’t – you can get really close to perfection.
My advice is to clean the concrete thoroughly before you start. You can accomplish this with a pressure washer that comes with a 15 degree tip on the end of the wand. By cleaning the concrete, you can see exactly what suits you.
After your clean concrete is dry, get on your knees and really look at it. Chances are you’ll be amazed. You will see the individual pieces of sand and tiny stones that the man-made stone was made from. Your first task is to go to local gravel pits and find sand that looks exactly as you see it.
Pay attention to the different colors of the sand as well as the grain size. You may need to mix and match sand from different sources to get an exact match. You have to get the sand right.
Now it’s time to look at the cement paste that’s sandwiched between the grains of sand in the concrete. What color is it: gray, polished, cream-colored? It’s probably a shade of gray. Gray is good and the easiest to find.
Do you remember when I talked about patience? You can only achieve perfection or get close to it through practice. You will be mixing a test batch of concrete yourself. Do not purchase the prepackaged concrete from the home center or local hardware store. Visit a local hardware store and grab a bag of pure portland cement.
You need clean gravel with stones from grapes to green peas. Mix three parts of the gravel with two parts of sand and 1.5 parts of cement. Mix everything dry and add water until the concrete is the consistency of stiff applesauce.
You can watch a video on askthebuilder.com called Mixing Concrete where I show the perfect consistency.
Pour this mixture into a small 1 foot by 1 foot mold and finish it so that the top texture matches the existing concrete as much as possible. Cover the test area with a new plastic garbage bag and secure it so that it does not blow off. Wait two weeks.
At the end of the waiting period, mix 1 part hydrochloric acid with 10 parts water. Read the warnings on the label of this strong acid and follow all directions.
Remove the plastic from the test area, spray the concrete with a little water and brush on the acid solution. It should start gushing right away. Apply more acidic solution and leave it on for about 10 minutes without letting it evaporate. Use an old brush to brush the concrete stain, rinse it off with plenty of clean water, and let it dry.
The acid washes the gray cement paste off the sand on your new patch so you can see the color of the grains of sand. If you don’t do this step, you will have a monolithic color of gray for years. You only do in a matter of minutes what Mother Nature has done since the day the driveway was watered.
There is a great chance that you have a close game. If so, celebrate and repeat your efforts on the actual driveway.
Are you like some of my friends and don’t have that patience? Clean your entire driveway and just mend the area as I indicated in the columns on askthebuilder.com. Buy penetrating colored stonework a month later and colorize your entire driveway. I have a video on askthebuilder.com that shows how to color Mexican tiles. It’s the same process for your concrete driveway.
The white color Donn asked for could be a traditional hydrated lime whitewash. It’s a great way to make your driveway monochrome. You can whitewash any color with dry pigments. Would you like to know how to do it? Just read all of my previous whitewash columns.
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