After the drywall installation in a room, trim carpentry can start. But there are a few things to be checked for first. Check all the surfaces that will have molding applied to them, using a straightedge and carpenters square.
Drywall compound will frequently have been built up along inside and outside corner joints, and your trim molding will not lay flat there. So, you need to flatten these areas out, taking off the high spots with a Stanley Surform tool, and paring down tight areas with a chisel where the Surform won’t reach.
Edges of door and window jambs should be flush with the drywall surface, but chances are that due to layers of building paper, miscellaneous minor discrepancies, and differences in thickness of studs, there will be spots where the jambs are not flush. If the drywall protrudes proud of the jamb more than 1/8 inch, it will need to be corrected to make the two surfaces flush.
One trick is to add a few more drywall screws or nails; this will sometimes be enough to “suck back” the protruding drywall just enough. You may also remove the protruding drywall area with the Surform tool. Shave away the drywall paper and core in a taper the width of the finished casing.
Be aware this is a messy job that will produce lots of dust, so wear a breather mask and put down a drop cloth if there is a finished floor in place. For major gaps of ¼ inch or more, you’ll want to add jamb extensions.
A jamb extension is a strip of wood attached to the edges of the jambs, in order to bring the jambs flush with the surface of the drywall, letting you nail the casings on. Extensions need to be the same wood as the jamb and the same thickness.
Saw the wood to the width needed to bring the edge flush to the wall surface, then glue or nail the extension on to the jamb. At the corners where the extensions meet, basic butt joints are good enough, since they will be covered by the casing.
You may have the exact opposite problem also, that is, the jamb protruding beyond the surface of the drywall. This case can be remedied by planning down the jamb surface flush with the drywall.
Watch out not to plane too deep, or you will damage the surface paper of the drywall. The best tool to use for this is a small block plane; for larger protrusions, a jack plane or power plane can be used also.
Plane down the jamb until just before digging into the drywall paper with the plane. A block plane will let you bevel the jamb so that the inside edge is slightly away from the drywall, which will ease installation of the casing.
When to Paint
Although trim is one of the last finishing touches to go on a house, there are different approaches on exactly when to apply it, mainly revolving around whether to install it before or after painting the wall and finishing the floor. The ideal sequence is:
1. Taping and Mudding Drywall
2. Installation of Wood or Tile Floor
3. Priming Wall and Uninstalled Wood Trim
4. Sanding and Finishing Floor
5. Install Trim and Cabinetry
6. Any Electrical, Plumbing and HVAC Remaining Installation
7. Painting/Staining of Walls and Trim
The above sequence requires detail hand painting of the trim, but often, painters will work exclusively with airless paint sprayers in order to maximize their productivity, and want the trim installed before they come in to a house to paint. What they do is mask off the walls, spray the trim, then mask the trim and spray the walls.
You can find airless painters who will agree to paint untrimmed walls, but the trim will need to be painted before installation, and touched up after being installed. Of course, if you are doing all the work yourself, you can do what you want, which should be to finish the floors, then paint the walls, then do the trim carpentry.