If your home was built before the 1940s and was not remodeled in the past 50 or so years, you probably have plaster walls. Aside from assuming, there are some practical ways to tell if you have plaster walls, including the following: If you knock on the wall and it feels solid, not hollow, if you can’t insert a thumbtack easily, if there are cracks that look like spiderwebs, or if your home has curved, arched, or swirled walls, doorways, or window openings.

If you have an unfinished basement or attic, you could examine the backs of any finished walls to check, too.

You should not leave drywall outside, especially overnight or in a wet, humid climate. Exposure to rain and humidity can damage the drywall, weakening its structural integrity and making it susceptible to mold growth. If you must leave drywall outside during a project, be sure to cover it with a tarp or keep it inside a storage shed to protect it. Even drywall intended for exterior projects requires a protective moisture barrier. For best results, store any extra drywall in a dry area away from the elements.

There are six levels of drywall finish, from 0 to 5, that refer to the amount of work performed during the finishing process.

Level 0: Drywall is hung with no finishing work.

Level 1: Tape is placed over the seams between drywall sheets.

Level 2: A thin layer of mud is applied over the tape and screw holes. This level is common for utility rooms or walls that will be covered.

Level 3: A full coat of mud covers the screw holes and tape, but the surface is not sanded. This is often used in garages.

Level 4: This is the most common finish for visible interior walls. It involves applying two coats of mud over seams and screw holes, with sanding between each coat, creating a smooth surface ready for flat paint.

Level 5: This is a high-end finish for luxury homes. It includes full taping, mudding, and sanding, plus a final skim coat over the entire surface before painting.

Very little. One inch of water can stain walls, warp wood, and create a perfect environment for mold growth. One to two inches of water can do significant damage to drywall, insulation, and electrical systems. Anything over that is considered an extensive flood, often resulting in severe structural damage.