Large gap between stair and stringer

[redhexagonal]

I have a U turn staircase. There is a large gap (18mm) on one side between stringer and plasterboard wall, while the opposite side is cut about 12mm into the plasterboard. The gap is currently filled with foam, filler and caulk. Its uneven and cracked so I’ve removed the filler/caulk and raked a bit of the foam out (it was filled level with the stringer).
How could I make this look neat and not crack? The stringer is 25mm

 

[RandomGrinch]

Scribe in a wooden moulding?

 

[Deleted member 174758]

The Grinch is right - the gap between the wall and the stringer is tool large to caulk in. You'll need to get some flat wooden profile, maybe 15 to 2omm wide) and if needs be scribe it to the wall and pin to the top of the stringer (jigsaw, block plane). Always better to have a moulding which is stepped back from the edge a few millimetres, like an architrave is stepped bacjk from the edge on a door casing

 

[redhexagonal]

The Grinch is right - the gap between the wall and the stringer is tool large to caulk in. You'll need to get some flat wooden profile, maybe 15 to 2omm wide) and if needs be scribe it to the wall and pin to the top of the stringer (jigsaw, block plane). Always better to have a moulding which is stepped back from the edge a few millimetres, like an architrave is stepped bacjk from the edge on a door casing

the gap itself is almost 20mm wide at the top, so it would have to be wider that. The other issue is that the stringer has some pretty horrible curves/angles in it going down to the first turn

 

[Deleted member 174758]

OK, make it wider. Even a piece of 2 x 1 PAR (44 x 22mm) softwood could be used for the task (albeit a bit thick IMHO). Door lipping (often 45/50mm wide x 6 to 10mm thick) would be easier to install

 

[redhexagonal]

OK, make it wider. Even a piece of 2 x 1 PAR (44 x 22mm) softwood could be used for the task (albeit a bit thick IMHO). Door lipping (often 45/50mm wide x 6 to 10mm thick) would be easier to install

The other issue is that the stringer has some pretty horrible curves/angles in it going down to the first turn.

 

[Deleted member 174758]

Thinner lipping will bend over that. Go to the mouldings in B&Q (or better a timber yard) and pull stuff out to see how flexible it is. Down at 5 to 6mm thickness timber strip is quite bendy. Alternative get a rip cut of 6mm MDF cut to size (local joinery shop, local timber merchant?). 6mm MDF is very flexible