Even though construction sand is not used for laying block paving or paving slabs until coupled with cement, and even then, the material might be too soft to put paving slabs over. This is due to the fineness of the sand. If you use soft building sand to install block pavement, the paving will ultimately sink. The best option is to use coarse grade gravel instead. Building sand is used in creating foundations because it is inexpensive and easy to work with. The sand can be used as a base for other materials, such as concrete, or by itself. It is also useful for making patterns and shapes, since you can change the shape of the container that you use for storing it. When building a foundation, first check with your local building department to make sure that you are using the correct type of sand for your project. Some sands are designed for certain types of projects while others are general purpose. For example, if you were building a house with a basement, you would want to use a heavy duty sand with larger particles than you would if you were just putting in a patio. Heavy duty sands can be found in grades 100-150. Lighter weights are good for finer finishes or when you only need a light base under a plant. Next, you will need to determine how deep you want your foundation to be. This depends on several factors including but not limited to your own taste and what type of structure you are building.