Construction · Lesson 7 of 13Beginner8 min read

Interior Finishes and Stairs

Finishes are the parts you see and touch: drywall, trim, doors, floors, paint and stairs. They go in last, after the house is weather-tight and the work inside the walls has been inspected.

Drywall

Drywall (gypsum board) is a sheet of gypsum pressed between two layers of heavy paper. Installers measure, mark and cut the panels to fit the plans, fasten them to the studs and ceiling framing, and then tapers cover the joints. The work often means lifting heavy panels overhead to fasten them to the ceiling.

Drywall also slows fire. Gypsum is calcium sulfate with water molecules locked into its crystals, about 20 percent of its weight, and it takes a lot of heat to drive that water out. The Being an Adult 101 guide to patching drywall explains the chemistry.

Each coat is thin and wider than the last; sanding between coats makes the surface flat. Sources: U.S. Bureau of Labor Statistics (what drywall installers and tapers do); NIOSH via OSHA (drywall sanding dust).

Taping and mud

The long edges of a drywall sheet are slightly tapered, so where two sheets meet there’s a shallow channel. Tapers bed paper or fiberglass mesh tape in joint compound (“mud”) across the joint, then add more coats, each a little wider and thinner, and sand between coats until the joint disappears. Screw heads get the same treatment. Thin coats dry faster than thick ones, and compound shrinks a little as it dries, which is why a deep fill may need a second coat.

Sanding makes fine dust, so keep it contained and protect your eyes and lungs. In older homes there’s more to think about, as the Stop box below explains.

Trim and doors

Trim covers the joints where drywall meets windows, doors and floors: casing around openings, baseboard along the floor, and sometimes crown molding at the ceiling. Installing windows, doors and molding is part of a carpenter’s job. Doors and windows only work smoothly when their frames are plumb (perfectly vertical) and square, which is why the framing and the measuring in Lesson 8 matter so much.

Floors

Finish flooring goes over the subfloor: wood, tile, vinyl or carpet, each with its own underlayment and installation instructions from the manufacturer. Flooring installers and tile and stone setters are their own trade.

Old flooring deserves care. EPA lists vinyl floor tiles, the backing on vinyl sheet flooring, and their adhesives among the products that may contain asbestos, and says you generally can’t tell whether a material contains asbestos just by looking at it.

Paint

New drywall and patches get primer first, then paint, so the color and sheen come out even. Paint is part of the envelope too: in cold climates, latex paint on the inside of an exterior wall can serve as a Class III vapor retarder (Lesson 6).

Old paint is a hazard to plan for. If a home was built before 1978, it may have lead-based paint, and the older the home, the more likely it is.

StopOlder homes: lead and asbestos

Lead: EPA requires anyone paid to do work that disturbs paint in homes and child-care facilities built before 1978 to be certified and to follow lead-safe work practices. Minor jobs that disturb 6 square feet or less of paint per room inside, or 20 square feet or less outside, are exempt, but window replacement and demolition of painted surfaces are always covered. The rule generally doesn’t apply to homeowners working in their own homes, but EPA urges them to work lead-safe: test first or assume lead is present, contain the work area, use power tools with HEPA vacuum attachments, and clean up with a HEPA vacuum and wet wiping.
Asbestos: material in good condition that won’t be disturbed should be left alone. Before a remodel that could disturb it, have it inspected. Don’t dust, sweep or vacuum debris that may contain asbestos.

Stairs

A stair is a set of risers (the vertical part of each step) and treads (the part you step on), carried by sloped boards called stringers. The front edge of a tread is the nosing. Codes also cover handrails, guards along open sides, and headroom above.

Laying out a stair starts with the total rise: the height from one finished floor to the next. Divide it by the tallest riser the local code allows and round up to get the number of risers; then divide the total rise by that number so every riser comes out exactly the same. There’s always one fewer tread than risers, because the upper floor is the last step. The local code sets the limits for riser height, tread depth, headroom, handrails and guards, and those rules vary from place to place.

The local code sets the limits for riser height, tread depth, headroom, handrails and guards. Every riser in a flight is made the same height.

Enter the total rise and the limits from your local code. The calculator divides the rise into equal risers and works out the run and the angle. Tap “Walk up the stairs” to climb it.

Finish parts and what they do
Part	What it does	Signs of trouble
Drywall	Gypsum panels that make the wall and ceiling surfaces and slow fire.	Nail pops, cracks at joints and corners, water stains.
Tape and joint compound	Hide the joints and fasteners.	Cracked or bubbled tape, visible seams.
Casing and baseboard	Trim that covers joints at openings and floors.	Gaps that open and close with the seasons.
Doors	Swing in frames that must be plumb and square.	Sticking, gaps, latches that won’t catch.
Finish flooring	The surface you walk on, over the subfloor.	Squeaks, gaps, cupping or lifting from moisture.
Primer and paint	Seal and color the surfaces.	Peeling or blistering from moisture.
Stair treads and risers	Make up the steps; all risers equal.	Loose or uneven steps, wobbly railings.

You canYou can

Patch small holes in drywall (Being an Adult 101).
Find a stud before you hang something heavy (Being an Adult 101).
Paint a room, working lead-safe if the home was built before 1978.

Check yourself

Tap an answer to check it, or open “Show the answer.”

What is the core of drywall made of?
Show the answer
Gypsum. Drywall is gypsum between paper faces. The water bound in gypsum crystals helps it slow fire.
Why is each coat of joint compound spread wider and thinner than the last?
Show the answer
To feather the joint so it disappears into the wall. Wide, thin coats blend the joint into the flat wall around it.
A floor-to-floor rise of 105 inches, with a maximum riser of 7½ inches, needs how many risers?
Show the answer
14. 105 ÷ 7.5 = 14 exactly, so 14 equal risers of 7½ inches, and 13 treads.
Who must be EPA-certified to disturb paint in a home built before 1978?
Show the answer
Anyone paid to do the work. The RRP rule covers anyone paid to disturb paint, including carpenters, plumbers and electricians.
Which of these may contain asbestos in older homes, according to EPA?
Show the answer
Vinyl floor tiles and their backing and adhesives. EPA lists vinyl floor tiles, vinyl sheet backing and adhesives. You can’t tell by looking.

Go deeper

Being an Adult 101: Patch a Small Hole in Drywall Patch a small hole, and the chemistry of gypsum.
U.S. EPA: Lead-Safe Renovations for DIYers EPA’s lead-safe steps for do-it-yourself renovation.
U.S. EPA: Learn About Asbestos EPA: where asbestos may be found and why it’s harmful.
U.S. Bureau of Labor Statistics, Occupational Outlook Handbook: Drywall Installers, Ceiling Tile Installers, and Tapers The drywall installers’ and tapers’ trade.
Lesson 8: Reading Plans and Measuring Next: reading plans and measuring.

Sources

I finished this lessonSaved on this device only.

A free course from Teddy Rook Book. It explains how houses are built in general and follows U.S. sources; the local building code, the building department and the manufacturer’s instructions are the final word.