There are a variety of tub types that you can choose from when it is time to install a bathtub in your home, ranging from cast iron to steel, acrylic and composite tubs. Acrylic is one of the most common because it is easy to create and uses plastic-based materials that are cheaper in comparison to the others. They are also much easier to install, but still have the strength needed to support the weight of a body plus water.
Nature of Acrylic Tubs
While acrylic is one of most flexible types of tubs and one of the easiest to install because of its lightweight components, it is also one of the least durable in terms of scratches and cracks if the tub is not installed properly. A cast iron tub, for example, can weigh up to 600 pounds before water is added, while an acrylic tub might weigh 100 pounds before water, depending on the type of acrylic tub you are buying. They are the budget solution for bathrooms.
Acrylic tubs are not designed to support weight on their own, as they are not stand-alone tubs. Part of the overall installation for acrylic tubs is a tub frame built out of the same framing material as the house, plus the tubs are set in a base. The combination of elements creates the support structure necessary for this plastic-based material to support several hundred pounds of water and the weight of human bodies, as the tub alone is not strong enough to withstand the pressure.
All acrylic tubs need to be set in a base of mortar or mud, such as concrete mortar or drywall mud. While the upper part of the tub sits on a frame built out of wood, the entire bottom of the tub needs to be supported by a contoured base that has hardened to fit the skin of the tub. This base of mortar/mud supports the weight of a human body as well as the weight of the water. Without this support, the acrylic tub would bend and crack within the first few uses.
The actual strength of a tub depends on the manufacturer and the type of acrylic they use, but they always rely on the strength of the surrounding elements that frame the tub in. As a general rule, tub frames and floors are meant to support a minimum of 40 pounds per square inch, and a structural engineer can help you decide if you need more based on your tub design plans.