Concrete blocks or concrete masonry units are classified into two main types: solid and hollow. Solid concrete blocks are made with dense aggregate, making them heavier, stronger, and more stable than other concrete blocks. For this reason, most architects and engineers prefer to use them for load-bearing walls. Meanwhile, hollow concrete blocks contain a void area and a solid area, making them more lightweight and easier to install. You can learn more about concrete block shapes in Guam by reaching out to a local concrete manufacturer or supplier, or by visiting a home improvement retailer that sells them. Not sure if your neighborhood hardware store does? Just call ahead and ask! Most businesses on the island are listed in the Guam Phone Book’s yellow pages section for your easy reference.