We sometimes remove enough material so that we can dab two (plum and straight) strips of plasterboard up each rough masonry jamb. Once set this gives you an ideal surace to fix the casing to.
We fix the hinge side back to the plasterboard and pack out the latch side.
Mark off your solid bricks before dabbing so you can identify where to fix to later.
At first I thought you meant to fix to the plasterboard!
I'd assume your method is:
- locate good bricks (nearly full, not a quarter for example) near where the hinges of the door will go
- dab the plasterboard onto these bricks
- fix the hinge case leg through the plasterboard and into these bricks, tight up on the hinge side
- fit the other leg, packed out to an opening of the door width + 6mm or so
Good call on the plasterboard, i dare say.
Other tips -
You're either fitting door cases that are pre formed with a thick part that the door stops against and a thin part that the door fits into (and this is what you measure when making the door +6 mm opening), or you're fitting a door stop bar afterwards - fit the stop after fitting the door, that way if the door is slightly warped the stop can be fitted to the warp for a consistent contact. When fixing cases to masonry, fix in the region that will be covered by the stop bar
If you're doing a lot of doors, buy a hinge jig and a 1/4 inch router. Buy hinges that have rounded off corners, or get a special punch that chops a square corner in one hit after you've routered the door/case. The screws that come with hinges are occasionally crap - the shafts are too thick and the thread not very deep, so they split the wood rather than bite it so predrill. Bear in mind that hardwood doors are probably softwood cored, with a 10mm or so strip of hardwood down the edge (dpeends how much the blurb says the door can be planed), when arranging good wood to get your screws to bite into