Foundations and Concrete - Thoroughly Explained - 1950

The video highlights the importance of builders in constructing various structures, from houses to factories. It focuses on the fundamental steps involved in building a durable foundation for a two-story administration building in a temperate climate, emphasizing that construction principles can vary based on factors like climate and soil conditions.

The initial step in construction is to accurately lay out the building's position on the ground. This involves using plans adhering to Navy specifications, measuring from known reference points (like street centerlines) to establish building lines, and driving hub stakes to mark corners. Triangulation is used to precisely locate all corners, including those for a central wing, and batter boards are set up at a predetermined elevation to guide the foundation's grade.

After laying out the site, a trench is dug to the required depth for the concrete foundation and piers, ensuring it reaches undisturbed earth. Forms, typically made of wood or steel, are then constructed to contain the concrete as it hardens, shaping the foundation. The foundation will be T-shaped, with a footing and a vertical wall, connected by a keyway to ensure strong bonding between the sections.

The video breaks down the components of the foundation form, including tie wires, spreaders, wales, stakes, braces, studs, and sheathing. It then demonstrates the step-by-step assembly, starting with cutting studs and sheathing to precise lengths using patterns. Sections are assembled on a workbench and then carried to the site, where they are joined, particularly at corners, using scaffold nails for easy removal later.

Stakes are driven along the inside and outside of the form walls, and braces are nailed to them. Two men work together, one plumbing the form with a level to ensure the sheathing is on the building line, while the other nails the braces. Whales, selected for their straightness, are toe-nailed to the form walls, and corners are securely locked by an overlapping arrangement of whales and additional nailing.

Inner form wall sections are put in place, maintaining an accurate spacing with tie wires and spreaders. Snap lines and accurately sized drippings are used to establish the exact level for the concrete pour. A core box is strategically placed to create an access opening. Anchor bolt templates are installed to secure the building's sills to the foundation, and forms for pilaster supports are also prepared.

The video explains how concrete is prepared, either by mixing on-site with a portable mixer for small jobs or more commonly, transported from a batch plant by a transit mix truck for larger projects. The batch plant precisely measures aggregate (sand and gravel) and cement, which are then loaded into the truck's revolving drum for mixing with water during transit to the construction site.

Before pouring, forms are thoroughly wet to prevent concrete from sticking. A metal chute from the transit mix truck guides the concrete into the forms. During the pour, it's crucial to rod the concrete by hand or with a mechanical vibrator to remove air pockets and prevent aggregate separation (honeycomb). Concrete is often poured in stages to allow initial setting and prevent form failure.

As concrete is poured, spreaders are removed, and excess concrete is screeded off the top of the foundation wall to achieve a preliminary level surface. A wooden float is used to further smooth the top of the wall. Piers are also poured and rodded, and metal stirrups are embedded to secure the girder later. The video briefly shows sidewalk pouring: screeding and bull floating to bring larger aggregate below the surface, followed by steel troweling, edging, and jointing for a finished look.

Concrete hardens over time, a process called curing. To prevent cracking due to shrinkage, concrete must be kept damp. After 3-4 days, the forms are carefully stripped, removing stakes, braces, tie wires, wales, and the form walls. The concrete, initially 'green,' will lighten in color as it fully cures. Salvaged form materials are stacked for future use.

Once the foundation wall is completed, nuts and washers are removed from anchor bolts. Termite shields are installed on top of the wall, and holes and joints are sealed with coal tar. Sills are cut, drilled to receive anchor bolts, and placed on the termite shields, ensuring they are level and aligned. Finally, the girder is fabricated, positioned on the piers, secured to the stirrups, and checked for grade, completing the foundation ready for building erection.