Plastering (bonding) over a steel lintel?

[TheStrayCat]

Im a bit concerned about applying bonding directly over a steel lintel holding up an RSJ in regard to cracking...

Is there a trick to it or some mesh or a product that is good for these sort of scenarios where movement between 2 different substrates?
Really trying to minimize cracking in the future... I was considering making up the thickness around the lintel in bonding and then making up the plaster thickness on the lintel (highlighted in yellow) by layering on 1kg of fibacryl as it has those flexible qualities (although application will likely be a pig!) with a view to help stop future movement. What do we think?

Avoiding cracking is my main concern and theres only about 5mm thickness from steel to plaster ao really no way of adding plasterboard or similar. along this 6m wall.

@Wayners - Any thoughts?

 

[TheStrayCat]

Anyone?

 

[Wayners]

Chip the plasterer off following your yellow box line you made in the picture. You only need around around 20mm below existing plaster edge and 15mm Ish deep. If all the plaster comes off back to masonry that's fine.
Lash on PVA 50/50 with water. Give it time to dry.
Then fit plasterboard over which will bridge the edge joint.
You can use board adhesive. That will stick to plaster/masonry and over the metal.
The plasterboard edge is the weak point so PVA the dry edges before dot and dabing so it all sticks as one.
If the board is stuck to masonry bridging joint and the metal moves, it won't split board.


Other option is to cut plasterboard strips to fit in.
PVA board edges and wall plaster.
Stick first board on metal with a polymer grab.
Dot and dab plasterboard to make up depth.
Fill and make good
If you PVA everything including all board edges it would flash dry from suction and crack and be solid. The bit of polymer holding first board will give a bit under.

Hope that makes sense...
Either option will work

I probably wouldn't bother using mesh tape. It will all be solid.

How deep is it? Maybe one layer of plasterboard will be enough

 

[TheStrayCat]

@Wayners - unfortunately not deep enough for plasterboard. 4-5mm.

 

[Wayners]

I'd lash with PVA and fill with a box of toupret powder filler then.

Can't do anything else

 

[TheStrayCat]

@Wayners - Funny you say that, that's kind of what i'd settled on. I was considering using their flexi-skim. Which has a great demo online showing off it's flexibity.... any experience with it?

 

[robinbanks]

Wallpaper it, so you don't see the cracks

Joking aside, if it does crack, can you affix some decorative overlay, wood trim etc?

Alternatively I think if you took it back as far as poss and fitted 9mm board I don't think you'd see the 4mm at the edges if it was feathered out over a reasonable distance..

 

[Wayners]

@TheStrayCat

Like this. 40cm is the one I used the most.
Sometimes the 60cm

Is that what you mean with flex skim?

I gave my plastic blades away. Never liked them.

https://www.amazon.co.uk/Skimming-Smoothing-Plastering-Flexible-Finishing/dp/B0BJDVZCK2/ref=asc_df_B0BJDVZCK2/?tag=googshopuk-21&linkCode=df0&hvadid=650847846199&hvpos=&hvnetw=g&hvrand=1613952331529237228&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1006741&hvtargid=pla-2022909143404&psc=1&mcid=6df41656651c3babb6e62a74f4fbbb12