Loose stringer

[jacko555]

I've spent the day understairs glueing and screwing as per the https://www.diynot.com/diy/threads/screw-size-squeaky-stairs.592566/ and found the stringer flexes as someone walks up the stairs.

It appears the stringer was attached to the wall with large cut nails. The plaster behind them has crumbled over the past century. So there's stringer, 1 inch ish gap, wall. The nails are loose and there's movement.

What's the best way to fix?

Torn between screwing some 2x4 underneath for it to rest on, or masonry screws through the stringer.

Neither solution is ideal. There's no consistent smooth end on the stringer for the 2x4 to butt up against (it looks like there was a rebate for a tongue) that's broken in places, so I'd need to pack and wedge.

For the masonry screws, I'd need to (I think) pack between the stringer and wall. Messy and lack tools to cut the correct depth.

Suggestions welcome.

@JobAndKnock all day I could hear your words taunting me that it would, in the long run, be easier to replace the lot.

 

[Deleted member 174758]

It appears the stringer was attached to the wall with large cut nails. The plaster behind them has crumbled over the past century. So there's stringer, 1 inch ish gap, wall. The nails are loose and there's movement.

What's the best way to fix?

Packer between the stringer and the wall (piece of 19mm softwood skirting or the like - plene to the required thickness or pack out with hardboard, thin plywood or horseshoe packers if not thick enough), drill through with a twist bit (but not into the masonry), swap to a masonry drill bit and hammer drill into the masonry (7mm). Push a 7mm brown masonry plug (or if needs be multiple plugs) down the hole and into the masonry then fix with a 5.0 x 100 or 6.0 x 100 screw (6.0 x 100 really needs an impact driver and will be a PZD#3). Repeat every 400 to 600mm up the stringer and it should stiffen things up quite well. I'd forget the masonry screws unless you are absolutely sure how good the masonry is - in any case 5.0 x100s with brown plugs are a lot cheaper and have a wider range of uses IMHO

@JobAndKnock all day I could hear your words taunting me that it would, in the long run, be easier to replace the lot.

Did you also hear me saying, "Been there, done that, got the T-shirts!"

OK, so I'm driven by commercial considerations (a guy's got to earn a living, after all) - but I couldn't see me being able to justify spending the time to do the repairs you've undertaken, especially with customer's money, There are times when it is better to cut your losses.

 

[jacko555]

For closure - I followed your advice (packed void with ply, 7mm brown plugs, 5x100 screws).

Stringer no longer flexes. Stairs no longer sound like a flock of seagull being slaughtered when you use them.

Apart from various aches from the contortions, satisfied with the job. Entire thing took a day and about 140 quid. (Needed more glue and a 150mm masonry bit)

Thank you @JobAndKnock, your advice has been priceless.

 

[Diver Fred]

May I add I'd have given the underside of the flight of stairs a good dose of woodworm treatment.

 

[jacko555]

There's no woodworm. The holey bit in the pic is crumbling lime plaster chunks.