Home Inspection and Drywall Basics
One of the most common deficiencies found during a home inspection is cracks in drywall or plaster. Cracks are common in plaster and drywall because they are brittle and rigid but are supported by materials that are not equally as rigid. Plaster and drywall are attached to flexible wood structures on foundations that rest upon compressible soil. Wood expands in humid weather and contracts in dry weather. Plaster and drywall are too rigid to move with the wood and therefore cracks will appear when there is any movement in the house or foundation.
Drywall installation involves nailing or screwing the sheets to the studs. Drywall installers cut the sheets to fit, and holes must be cut to accommodate pipes and mechanical equipment. The sheets are then fastened to the studs in a process called hanging. While most drywall installation used to use nails, screws are now the most common. Drywall is normally installed perpendicular to (across) the ceiling joists and wall studs, and the ceiling is always installed first.
Special moisture resistant drywall is used where excessive moisture may be a problem, such as bathrooms. In most cases, the moisture resistant drywall is green. Fire-rated drywall (Type X) is used where building codes require it. Typically in garages and under stairs.
After the drywall is installed, special metal corner strips (“corner bead”) is installed on all corners. This helps to protect the edges of the drywall and provide a nice straight finished edge. Joint compound (drywall mud) is used to finish all joints, nail heads and corners. In most cases, two or three coats of compound are needed at all taped joints. The texture coat is applied last.
The finished quality of your drywall will have a large impact on the beauty of your home. Most drywall cracks can be eliminated by just applying joint compound, but plaster cracks should be widened to 3/8 inch down to the lathe cleaning it out and wetting it with Elmer’s glue diluted 50% with water. If sections of plaster are disconnected from the lathe, they can be secured with “plaster buttons” prior to plastering the crack. Press fresh patching plaster, not joint compound, into the crack so that it is forced into the spaces between the lathes.
When plaster ceilings are full of cracks, apply drywall directly over the plaster and don’t bother patching. It’s just not worth the effort. Make sure the drywall is screwed to the floor joist or strapping and not just to the lathe.
Buildings built between 1930 and 1950 may have metal lathes under the plaster. You’ll notice when you try to hang a picture! You can distinguish between metal or wood lathe by hitting the wall. Metal lathe walls tend to be much stiffer.
This home maintenance tip and maintenance advice is brought to you by the Barrie Home Inspector and Orillia Home Inspector