Fitting door casings is considered a first fix job. When they are fitted, the goal is to create a completely even opening, that will accommodate a door as neatly as possible. This means the legs should be completely plumb and free from any bellies and twist. Also the head should be completely level.
The better the casing is fitted, the easier it will be to hang the door, as this will be fitted to the casing. If it is completely straight, twist free, plumb, and level, the work needed on the door will be far easier to make it fit.
Another consideration when fitting a casing, is the overlap on each side. The frame will be deeper than the wall it is being fitted in. Therefore, when fitting, you should ensure this is even on both sides of the wall.
For example, the casing timber may be 30mm wider than the wall. This would accommodate a 12mm plasterboard and skimmed plaster on each side. The goal would be for the plaster to finish as flush as possible with the fitted casing.
So, which comes first? Do you fit the door casing before or after the plastering is done?
As a general rule, the plastering will be done after the casing is fitted. This will include boarding up to the casing and then skimming flush with the timber. This provides a nice seamless finish. Following this, your architrave will be fitted to cover any gaps or rough edges.
Is plastering first fix or second fix?
Basically, before the plastering is done, all other trades will have completed first fix.
The electricians will have run all their wires and fitted things like back boxes for switches and plugs.
Plumbers will have fitted all their pipework ready to install radiators and boilers etc.
Joiners will have done things like, built studwork, fitted door casings, window boards, etc. As well as even earlier jobs like fitting joists and floorboards.
Plastering is the last job carried out after first fix. It is also the first job carried out before second fix. I would consider it, the job that transitions between first and second fix.
If you were to split plastering into either category, I would say that boarding and preparing for skimmed plaster is the end of first fix. Following this skimming and finishing the surface is the beginning of second fix.
Would you ever fit a door casing after plastering
The obvious answer to this is yes. If you are replacing a door casing in an existing property, then you will have no choice. In this scenario you will need to fit your casing to the existing finished walls.
The only caveat to this, would be if you need to remove damaged plaster. It is also worth noting, that when you remove the existing casing, it is possible, that you could damage the existing plaster. In this case, you would finish the job by skimming back up to the fitted casing to fill any gaps.
One challenge when fitting a casing to existing plastered walls, is you don’t know the condition. This doesn’t just refer to the plaster condition, but also the walls and the opening.
For example, there is more chance of the opening being slightly out of plumb and/or level. If this is the case, you need to fit to the existing plaster. Whilst at the same time trying to make your door casing as well fitted as possible.
This will usually mean that the door casing needs more packing and adjusting to fit well. There may also have to be some slight adjustment to allow the casing to be both:
- A good fit for the door you hang in it.
- And a good fit to the walls it is being fitted into.
For example, let’s assume one side of the opening is plumb and the other isn’t. If you fit perfectly to the existing wall, one leg of your frame will be out of plumb. This will cause twist in the casing and your door won’t close properly.
On the other hand, if you fit your door frame perfectly plumb, it will not line up with the wall. This could cause it to jut out in areas, which may make things like fitting architrave more difficult.
Usually the best option for this, is a compromise between the two. You should try to even this twist out over each leg. This would mean much less twist, that would be unnoticeable. As well as a neater finish with the existing walls.
If the problem is really significant, your best option would be to strip back the plaster a reasonable amount around the door. If you do this, you should be able to fit your frame plumb. Then you can plaster back up evenly to the new frame.
Conclusion
In any situation where you are working on bare unplastered walls, you should always fit your door casings first.
By fitting in this order, you will achieve a neater more seamless finish. Plasterers will skim as flush as possible with the door frame. This will provide a nice flat transition that is perfect for your architrave and skirting in second fix.
As we mentioned, in existing properties you will usually need to fit into existing plaster. I think you will agree, the example given, gives a good demonstration of the potential issues of fitting to existing plaster.
