Final answer:
Yes, mastic is typically needed underneath the flanges of accessory items in construction projects to ensure a secure and watertight seal.
Step-by-step explanation:
When it comes to construction, mastic is commonly used for various purposes. In the case of accessory items, such as flanges, mastic is often needed underneath them to ensure a proper seal and prevent leaks. Mastic acts as an adhesive, creating a strong bond between the accessory item and the surface it is being installed on.
For example, let's say you are installing a toilet flange onto the floor. Applying mastic underneath the flange will help secure it in place and prevent water from leaking between the flange and the flooring material.
So, to answer your question, yes, mastic is typically needed underneath the flanges of accessory items in construction projects to ensure a secure and watertight seal.