After I have installed all the cabinets and interior doors I am ready for the door and window casing. There can be an infinite variety of trim styles. Anything from a simple design with two side legs and a piece of head casing with mitered corners to a complex design with plinth blocks and a layered head casing that can have as many as seven pieces or even more not counting the returns. I know some carpenters like to do paint-grade trim packages more than the stain-grade ones because the gaps will be filled and painted. I will put the same effort into each. I figure if I use the same methods to case out all the window and door openings I work on I will be more used to the method and it will come more naturally. Besides that, it just bugs the heck out of me to leave a gap that everyone will see until it gets finished. I like to think that every trim job I work on is a resume for the next one.

   I will begin the casing process by pre-cutting all the pieces of door casing I will need. I cut the side legs first. That way I can use all the pieces I have leftover for the shorter lengths I need like the head casing and the window trim. Next I cut the longer pieces of window casing. This gives me more off cuts for the smaller pieces I need. This method uses the molding more efficiently and gives me less waste. Finally I cut the head casing and the smaller window trim.

  Simple mitered door casing

   When I precut the casing for this style I will first check for any imperfections in the wood that can't be sanded out. Then I will square off the end that will be at the bottom of the door. If there are any splits in the wood I will cut enough off so I know it won't crack in the same place again. For all the doors that will be over a carpeted surface, or a floor that will be installed later like tile or pre-finished wood, I cut the miter at the top at a length that will give me about ¼ inch gap at the bottom for the carpet to tuck under the door. For all the doors that will be going on a hard surface like a wood floor that is already installed or a vinyl floor I want the door trim to be tight to the floor so I will cut the door legs a few inches long and just cut the top square also. I will mark and cut those pieces as I go. For head casing I will cut a miter on the left end and let the right end run a few inches wild. This end I will mark and cut as I go also.

   After the casing is cut and laid out next the openings where it will be installed I will begin to fit it. I like to leave a reveal of 3/16 inch between the inside of the door casing and the edge of the doorjamb. I have done this so many times that I am comfortable with using my eye to get an even gap around the door casing. For someone who is not comfortable with this method I suggest using a tri-square. Simply set it with the ruler at the desired reveal and place the square in the corner of the doorjamb and lightly mark the side and head jamb. I will take a couple scrap pieces of casing with miters already cut on them and test how they fit. With the scrap casing set with an even gap along the doorjamb, the casing should make contact all along the miter. Sometimes the door will have to be installed so the drywall stands proud of the jamb a little, especially if the wall was a little twisted or out of plumb. In this case the drywall must be removed until the casing makes solid contact all along the back. If it only stands out a little you can, usually, get by with either crushing the corner with a hammer or cutting it down with a utility knife. If there is a significant gap I will set the casing in place with a slightly narrower reveal than I want to end up with and lightly mark the wall along the outside of the casing. I then score the wall with my knife about ¼ inch inside this line to cut the outside paper layer. I then hammer the wall inside this line to remove the paper layer. I then set any screws or nails in the drywall deeper and scrape the loose drywall away with the claw of my hammer or a putty knife. If this isn’t done you will end up with either a gap between the casing and the wall or the jamb. If the top or bottom of the miter makes contact and not the rest it means the doorway is set out of square. In this case you must cut the miters on your finished casing a little over or less than 45 degrees to close the gap. You must be sure to cut both sides of the miter at the same angle or the detail on the molding will no longer line up.

    A more common problem is that there is a gap at the face of the miter but the back makes contact or vice versa. This means the miter is good but you will have to back bevel the miter a bit .If there is a large gap I will bevel both sides as I cut them taking half of the bevel from each side. If there is only a small gap I can take the bevel off the miter on the head casing. To start the installation I will place the casing for both sides in place one at a time tight to the floor and mark the length on the inside of the miter where my reference lines are on the jamb and cut them with any bevel I have determined they require. I cut the left side to the exact length and I cut the right leg about 1/8 inch too long. I nail the left leg in place to the jamb with 18 gauge brad nails. I then nail the outside of the casing to the wall with 15 gauge finish nails. This way I know the trim is tight to the wall. If I nail the outside of the casing after the miters are together it can pull the miter apart. With the left leg in place I put the head casing in place with an even reveal with the jamb and check how the miter fits. I will re-cut the miter as necessary to get a good fit and mark the length on the right side as before and cut it to length as well. I glue the mitered edge where it fits to the left leg and nail it in place with brads for the first six inches and one brad through the edge of the miter from the top. I then take the casing for the right side and check the fit with the head casing. I will adjust the cut as needed and cut the length at small increments until I have an even gap all around. When I am satisfied with the fit I will finish nailing the head casing along the inside with brad nails and then the outside with finish nails. I then dry fit the last piece to make sure it still fits. I then glue and nail it in the same manor.