I'm writing about what must be a common problem in Winnipeg due to the severe winter weather here.
I have a house in River Heights, which I purchased in 2001 after you did a pre-purchase inspection for us. When we bought it, the concrete front porch had separated from the house, and had to be replaced. We hired a concrete contractor who did the job in September 2001. He demolished the old porch and steps, and rebuilt them with fresh concrete. While he was on the street, he also did some repair jobs for two of our neighbours. They don't seem to be having the same problem; so I assume it wasn't a substandard mix.
Since then, we've had to have him back three times to resurface the steps and/or the porch. Every year after the winter, there has been serious crumbling and flaking of the concrete in many places. Because the porch doesn't have an overhang, it is exposed to all kinds of winter weather. As you know, on many occasions we get freezing rain, which must be melted or the steps can become hazardous. I have never used salt on it, but have used two different kinds of ice melting compound, both of which claim they are safe to use on cured concrete.
My first question is: Could this be what is causing the flaking of the concrete surface? If so, what would you recommend doing to keep the porch/steps free of ice when this type of weather occurs?
My second question is: Is there anything you would recommend doing to prevent this from happening, such as laying down outdoor carpeting, or painting the surface with some sort of preservative?
Thanks for sending in your recent inquiry. It is always nice to hear from a former client, especially with a good question about a new issue with a repair or renovation since the purchase of the home. I will attempt to offers some explanation for the problems you are facing and offer a possible solution.
When the surface of newly poured concrete flakes, also known as spalling, it is usually due to a defect in the concrete itself or the at the time of installation. Concrete is a mix of cement, water, sand, and aggregate material (stone). There are many factors that may cause this mixture to cure improperly and cause the spalling you are experiencing. If there is too much or too little water in the mix, it may set up too quickly or too slowly and the surface concrete may be rough or flake off. If the temperature outside is too hot and the concrete is in direct sun or it is very windy when the concrete is poured it may affect the setting time. The moisture in the mix, which rises to the surface after pouring, may dry too quickly, leaving a bad finish. If it is too cold, the concrete may freeze before it is properly cured and may be damaged. If the concrete is not properly vibrated or tamped it may have too much air entrenched or have the aggregate settled to the bottom. Any of these things may affect the end product.
Wet concrete is poured into forms, normally wooden or steel, which hold the material in place until it is sufficiently cured. After pouring and levelling this mixture, it is normally allowed to partially set before trowelling to provide the desired surface finish. This is the most finicky part of the process and a good concrete finisher will know the precise time to start the trowelling and not over work the surface. Often a coarse brush or broom may be used at the end of this stage to give the steps a rougher texture to avoid slipping. If this finishing step is done improperly due to weather conditions or a problem with the concrete mix, it may be impossible to remedy. This is probably the most common cause of damaged surfaces in new concrete.
The other possibility is that the ice-melting compound you are using is not as safe as advertised. If the salts or chemicals in the compound react with the cement in the cured concrete it will cause surface damage. I suggest reading the instructions more closely as they make contain a warning against using on concrete that is less than several years old. If this is not the case, I suggest contacting the manufacturer directly to see if they have an answer or have experienced this problem.
To answer your final question, there may be a couple of relatively simple things you can do to help prevent further deterioration. Water seeping into the concrete from ice, snow or rain is actually the cause of the spalling and anything that prevents this from happening may help. Shovelling snow shortly after falling may the first line of defence. Carpet is the wrong solution, as this will hold moisture against the concrete, when wet, and make the problem worse. You may be able to paint the surface of the concrete with a non-slip paint designed for concrete. You can also use regular concrete paint and sprinkle in fine sand, to help prevent slipping in wet conditions. This should be done after the surface is refinished and allowed to cure, but well before the weather goes below freezing.