The maximum gap at the top should be 5mm or less - about the most you can caulk without it falling down the 'ole. Bigger gaps cap be filled with Fossa Caulk Saver then caulk added (a technique sometimes used on old buildings wth existing skirtings that have big gaps). You aim to get the skirting to fit as near to plumb as possible
before you start fixing it (see below) as well as sitting flat to the floor to prevent draughts. MDF skirting can easily be bent in to the contour of a bowed wall much more easily than pine and will also bend downwards to a meet a hollow or arched floor more easily as well.
There are two main problems you get with walls for skirting; firstly the wall is bowed along it's length (but acceptably plumb). This can even occur in new houses - most often because corner beads in the plastering are sitting proud. In these cases you need to fix one end of the skirting to the wall, then bend the skirting in to the wall with your knee and hold it there whilst you fix it. If needs be fix a temporary block to the floor to hold the skirting in place it whilst you do this and until the grip adhesive goes off (same applies to walls which are bellied out, only in that case the temporary blocks go at the outer ends).
Another, more serious, defect you get at the bottoms of walls is ropey plasterwork where the plasterer starts his stroke at that point and leaves a thicker area of plaster, so you just can't get the skirting in plumb and there is a big gap at the top if it is plumb. I find the best solution for that is to pencil line where the top of the skirting should go using an offcut of skirting, then reduce the thicker plasterwork to plumb (but probably quite rough) below the line with a hammer and electrician's bolster chisel or a large old wood chisel so that the skirting will sit flat and upright to the wall (this is a joiner's solution). I have on occasions resorted to planing out the back of the skirting with a power planer to get things to fit a really ropey wall, but that is mainly for hardwood skirtings and is really a "solution of last resort"
Also, as it stands, you simply cannot see what is happening at floor with the skirting if you leave those spikey carpet strips in the way (i.e. is the skirting flat to the floor or does it need bending or scribing to the floor to reduce the gap?). So lift them out carefully with a thin bar or wide chisel, before knocking the snot out of the plasterwork, installing the skirtings, painting the skirts,
and then refix them. You'll never do a decent job with that carpeting carp in the way (and the deco might struggle, too).
50mm ovals are maybe a bit on the big side, you know, 40mm are thinner, and
why are all the nail heads left sticking out? If you can't punch the nail in below the surface and if they bend like that then you are obviously trying to use nails that are too long for the job
You can use ovals providing you ensure that what you are fixing into will actually take and hold a nail
and that you can punch the heads under. Ideally this means fixing into the stud wall sole plate (bottom 45mm or so of the wall), looking for wooden studs to fix into, or adding wooden plugs if needs be. If the wall is something like a hard brick with a thin skim of plaster or render your only choice is going to be to drill 7mm, brown plug then screw (4.5 or 5.0mm screws). Plaster on soft brick and you can often use masonry nails rather than ovals. Plaster on soft block (such as Thermalites) and you can just nail double skew (dovetail nail) with biggish ovals, because they'll hold.
If the plaster is firm enough and thick enough you can get away with just double skew nailing
and using a grip adhesive on the back of the skirting. The technique for nailing to plaster is to drill two pilot holes at an angle in different directions with a small drill bit (or even just snip the end of a nail, chuck that and use it as a pilot drill), tap the nails in 3/4 of the way into the holes (aligning them with the grain of the wood), position the skirting against the wall, then finish with the hammer and punch under with a hammer and nail set. If you are using a lot of nails it is generally better to pre-drill the skirting and tap all the nails in
before planting it on the wall. BUT THIS ONLY WORKS IF YOU HAVE ALREADY SORTED OUT THE PLASTER (AS ABOVE) SO THAT THE SKIRTING PLANTS PLUMB AND FLAT TO THE WALL. IT ISN'T SUITABLE FOR POOR QUALITY AND SOFT PLASTERWORK NOR FOR WALLS WITH VERY THIN PLASTERWORK OVER MASONRY IN WHICH CASE DRILL, PLUG AND SCREW (capitalised to emphasise how important this is)
Despite comments, joiners
nailed skirtings into place for something like 350 years before we had 2nd fix nail guns in the late 1990s/early 2000s. It was the norm, but as I said above you always try to find a wooden stud, timber sole plate, timber ground or wooden plug that you've hammered into the wall to fix to (which is incidentally where the name "plugging chisel" comes from - a chisel designed to cut out mortar between masonry so that a wooden wedge or plug can be hammered in).
I also notice that you have a joint beneath that radiator. How the heck are you going to sand that flat?
View attachment 265217
Whilst can be a good idea to hide joints beneath skirtings,
that is only if you can plane or sand them flat afterwards! Also that joint is terrible!!! I've found that doing my joints at about 25° to 30° bevel works better for me, especially if I Mitre Mate the joint. But joints do need to be made as flat as possible and you do need to be able to get in there to plane/sand the joint absolutely flat afterwards - what you have done makes it impossible to get a smooth joint in there, so that will always stand out like a sore thumb. I had a 1st year apprentice last year who did a lot better than that - so considering that you charge for your work, that scores 2/10.
Another thing which is wrong is the way you have finished the skitrting into that "architrave":
View attachment 265225
In point of fact either that archtrave looks like it has been installed the wrong way round - the radiused edge should go to the opening side, the wall side, where the skirting meets the architrave is supposed to be flat. TBH I'd just want to rip that off and replace it with architrave fitted the right way round. Given that the architrave is a FU you've at least
started the right way to tackle this by bevel cutting the end of the architrave, but then you didn't scribe the back of the skirting to to fit the radius (requires a rat tail wood rasp, etc). Filling that now will just look like another bodge job.
If you can't take the architrave off (although why I really wouldn't know, as it
is carp), there is another solution, but it requires a multitool and a neat methodical approach:
View attachment 265228 View attachment 265229
1. Starting with the architrave and a line marking the top of the skirting, mark out then cut away the radiused section of the architrave
View attachment 265231
2. Cut some square edged material and trim th fit the gap. Glue in place. When set clean-up glue squeeze-out, plane flush, fill gaps with 2-pack filler then machine sand (because 2-pack
cannot be hand sanded effectively). Infill fillet shown in a different colour for clarity
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3. Install the skirting - you now have a flat edge to finish to - which is what you should have had to start with. It is still a little bit awkward compared to what it should look like if the architraves are properly installed:
View attachment 265235
but done properly it's a heck of a lot better than mitreing it then trying to bodge it with filler. Replacement is faster, though
At least your scribe at the other end is somewhere near, although there is still too much of a gap on the vertical, where it will be most noticeable and where you can't fill. Are you applying enough back set to your scribe cuts? (5°) Also you do need to learn not to chip the edges the way you have.
View attachment 265236
It may seem awkward, but the way to control the cut is to turn the blade so the teeth point towards the handle of the coping saw, and make the cut with the handle on the underside of the cut, so that the teeth are cutting into the material, and the blade is kept in tension (stiffer - straighter), so no break out. This is how fretworkers make cuts - at least half the joiners I've ever worked with don't know or seem to understand why you should work this way. Whilst this isn't as critical on unfinished MDF or softwood, it essential if you ever install pre-finished stuff or are working with splintery hardwoods, etc
For anyone who has read thus far but who isn't aware,
the OP is a tradesman who is charging for his work. I therefore hold o