Fresh Plaster Cracks

JJs Left Hand

Good evening all,

I got my house plastered just before lockdown. Rather than having a standard fascia/soffit arrangement I finished my gables with an aluminium slate trim which incorporated a downstand and plastered up to the underside of the projecting part of the trim (over the downstand).

Prior to starting I asked the plasterer would we need expanding mesh over the trim and he said no, he'd just put a heavy scratch coat on it and it'd be fine. So, trusting the expert I let him go with his suggestion.

The plastering is excellent to be fair to him however the inevitable has happened and I'm getting hairline cracks at the eaves along the line of the trim. They're not deep but with the frost the last couple of nights they are widening and as we're in May I'm very worried about what will happen come autumn and winter.

I've said it to the plasterer and he's going to look at it when he's out to do the internal plaster to see what he needs to do to remedy it. I've also talked to a painter who says they'd rake it out, brush in some flexible sealant and paint over it and he says it'll be fine but I'm annoyed with myself for not backing my original judgement and making him use the mesh so I'm looking to gather as much information as I can on this to see if there's a good solution out there.

So, anyone have any experience with this kind of thing and how do I solve it?

I can't seem to add photos in this post so I'll figure out how to do that and post them.

JJs Left Hand

Photos

sydthebeat

any pics of it before plastering?

was the blockwork carried up or was the gable rafter plastered over?

mickdw

As you figured yourself, this was always going to be an issue.
If you.must plaster over this trim and im not convinced it is a great idea, id suggest additional fixings and expanded mesh but im sure there is a better detail.

JJs Left Hand

No photos but last truss is just inside the inner leaf of the wall.
Blockwork carried up to align with top of truss.
Cavity closed and battens carried over top of wall.
So the trim is covering the end of the battens/felt and then plastered over.

Scratch coat was on it for about a month if not longer and no cracks along the trim although I'd be lying if I said I was forensically checking it.

When the sun shines on the wall the render obviously swells and closes the crack but once the sun moves away it opens again and it's only going to get worse I'd imagine.

Fuming with myself.

sydthebeat

i just find it weird that it didnt separate at the trim.... it separates about 150mm below it.

was there a big mortar build up over the blockwork to create the slope??

JJs Left Hand

https://www.tegral.com/en/products/slate/co2-aluminium-trim

That's the trim so it's cracking at the bottom of the downstand.

Not sure what slope you mean?

sydthebeat

JJs Left Hand wrote: »

https://www.tegral.com/en/products/slate/co2-aluminium-trim

That's the trim so it's cracking at the bottom of the downstand.

Not sure what slope you mean?

ah i get you now.. thats a full gable trim.

i though you meant something like this:



and yes... should have absolutely put on an expanded mesh ayer,

anywhere two different materials meet, they will always move independently and cracks are inevitable.

JJs Left Hand

Aye. Nothing I can do now bar try to fix it. Any ideas?

sydthebeat

JJs Left Hand wrote: »

Aye. Nothing I can do now bar try to fix it. Any ideas?

Chip it off to 100mm below the trim, fix expanded mesh totally covering the trim, and plaster again

JJs Left Hand

Was afraid you were going to say that!!

Sound for the input

sydthebeat

JJs Left Hand wrote: »

Was afraid you were going to say that!!

Sound for the input

it will ALWAYS bug you if you dont....