Carpet that is attached to a concrete floor is usually held down by adhesive. Unfortunately, when you remove the carpeting to replace it, the adhesive usually does not come off with the carpet in all areas. Instead, what is often left behind is course sections of dried adhesive that have bonded to the concrete floor in such a way that they are very difficult to remove. Separating the adhesive from the concrete is essential in order to properly clean and prep the concrete for new flooring installation.
Use a handheld floor scraper for small jobs. Hand-held floor scrapers have sharp blades that efficiently separate the adhesive from the concrete, so that it can be easily swept away.
Sweep the concrete floor well using a broom and dust pan. Follow up with a light vacuum, using the vacuum's floor attachment. The concrete floor should be completely free of all adhesive residue, dust and dirt before applying a cleaning solution.
Fill a bucket with approximately one gallon of water and a few squirts of dish soap. Thoroughly, mop the concrete floor; wringing the mop out in between to make sure that you do not over saturate the concrete floor with water. Change the water as you go if it becomes too dirty.
Allow the concrete floor to air dry overnight before re-carpeting or performing any installation over top of it. Otherwise, you can create a mildew problem if water is trapped between the concrete and the new flooring.
For stubborn adhesive that seems impossible to remove, use an adhesive remover along with the hand scraper. It may get messy, but at least you will be able to remove the old carpet adhesive. Just make sure that you open all the windows to make for proper ventilation. Rent a floor scraper machine for bigger jobs. Local home improvement stores often have floor scraper machines available for rent that can minimise the time it takes to remove carpet adhesive over a large area. These walk behind machines have a blade that can be adjusted for wood floors or concrete.
If you are cleaning the concrete floor after removing carpeting, in preparation for laying down a new floor, it is imperative that you do not skip removing the adhesive. Doing so will interfere with the new layer of adhesive that is used to lay the new carpeting. And if you are replacing the carpeting with tile, the left over, bumpy adhesive will make it impossible to lay the tile evenly.