Building new door frame

[DanGB]

Hi all,

As part of my kitchen renovations, its getting a new door frame/liner.
The old one was in awful condition plus a non stand door width.
Im widening it to suitable for 762mm door width.

Few questions.
The wall seems an odd thickness (1930's house), at the top its 80, and further down its about 77mm.
Im going to skim the walls after the door frame is on, so the frame will be about 86mm thick.
I was going to make the sides out of this wood, and plane it narrower to suit:
http://www.diy.com/departments/timber-smooth-t29mm-w89mm-l2400mm/249697_BQ.prd

The original top piece I have left in. This appears to be acting as a lintel, which just bricks above it, is this correct? If so, I'm wary of removing it, and may leave it in.

Is mortar right to use to fill the gaps between the uneven wall edge and wood lining?

One side of the door is against the wall. any tips on doing the door frame/architrave when its against a wall?

Many thanks,
Dan.

 

[Deleted member 174758]

The old one was in awful condition plus a non stand door width.
Im widening it to suitable for 762mm door width.

In which case you'd be able top get a standard door lining/casing kit with a rebated head joint from a timber/builders merchants. Some yards will rip kits to the appropriate width so all you need to do is give it a quick pass with a sharp jack plane. They should aso be able to supply lengths of planed stop lath for un-rebated linings. Beware! There are lots of poor quality, knotty monstrositis out there masquerading as "quality lining kits" (a bit like B&Q selling banana pine and calling it wood, really)

The wall seems an odd thickness (1930's house), at the top its 80, and further down its about 77mm.
Im going to skim the walls after the door frame is on, so the frame will be about 86mm thick.

TBH that's nothing unusual. The lining/casing will need to be wide enough to accommodate the thickest part of the wall so I'd normally just rip down the next widest stock size to suit

The original top piece I have left in. This appears to be acting as a lintel, which just bricks above it, is this correct? If so, I'm wary of removing it, and may leave it in.

Yes, I'd leave it in as well. The wall above needs more support than you'll get from a 30mm thick lining!

Is mortar right to use to fill the gaps between the uneven wall edge and wood lining?

No. The best way to do it is to plumb-up and fix the door casing/lining on packers, screws and plugs and then to foam-in the casing with expanding PU foam. To do it properly you'll need either a 6ft level or a shorter level taped onto a 6ft length of straight softwood (e.g. a 3 x 2 PSE - but it MUST be dead straight). We use AFFF (pink) fire foam on bigger, but that's not necessary for a stand-alone domestic property - the basic cream stuff will do as well. Do it on a warmer day, though (when the temperature is above 4 or 5 degrees), because the stuff doesn't work when too cold - and wear gloves in case it gets on your hands

One side of the door is against the wall. any tips on doing the door frame/architrave when its against a wall?

Depends in part on the style of architrave. If it's wide enough I'd either rip down a length of architrave with a circular saw and scribe that in to the wall, or possibly just run an appropriately-sized quadrant bead up that side of the lining/casing. If it's a complex architrave moulding or the moulding would be less than about 10mm wide I'd probably be satisfied with a architrave leg on one side only plus the head and nleave the other side bare

 

[DanGB]

Thank you @JobAndKnock for the very comprehensive reply as ever.

I'm interested to know why you would recommend expanding foam rather than mortar to fill up the gaps? I amk presuming that you are implying that there is no strength needed once the frame is screws to the wall with the packers/fillers.

How would you recommend afixing the side frames to the existing top lintel, is would that probably not be necessary as the architrave would provide the fixing together.

 

[Deleted member 174758]

I'm interested to know why you would recommend expanding foam rather than mortar to fill up the gaps? I am presuming that you are implying that there is no strength needed once the frame is screws to the wall with the packers/fillers.

Mortar will tend to crack where it abutts the casing/lining in any case, but foam literally "glues" the casing/lining into the opening and it will stop draughts dead. We tend to use it on commercial builds because it's less messy than mortar (no mixer/spot board to clean afterwards), faster to install (2- to 3-minutes per casing - mmaybe 5 minutes with a Staley knife to clean-off excess when it has all set), won't put moisture into your brand new casing/lining causing it to swell and potentially move (especially important if using MDF casings) and because we are often working in a fire control environment we use AFFF (pink) fire foam which helps prevent the spread of fire/smoke. To give you some idea of the strength of foam, if you removed the screws holding the casing after the foam had set the foam alone would hold the door casing in place even after you'd hung the doors, especially if the architraves were fitted (they stiffen the whole lot up as well) - mortar just can't do that

How would you recommend afixing the side frames to the existing top lintel, is would that probably not be necessary as the architrave would provide the fixing together.

I wouldn't fix the head at all. You normally just fix the legs (four fixings per side) and leave the head alone on single width doors. I'd normally only put a fixing or two into the head if it were a double width casing or lining - to prevent sag in the middle. A wee bit of foam between the head and the lintel will in any case give you an excellent fix