EML galvs vs SS (rendered dormer cheeks)

Hi
I'm doing a new post as this one isn't open for further replies - https://www.plasterersforum.com/threads/riblath-galv-or-stainless.47004/

Its this usual debate about galv vs SS EML. In this case, dormer cheeks (6x) on a self build chalet bungalow. I've more or less already decided on galv because of the massive price difference and i'm stretched on budget. Seen pricing for 8x2' sheet at £5 for galv and £25 for SS, £20/sheet x say 20 sheets is £400 extra!

Also I've read a lot of stuff on forums. While there's masses of arguments for and against, on balance it seems like SS is basically an insurance policy. Whereas in normal circs (I'm in Hertfordshire so not on the coast... house is averagely exposed) galv should be fine for 10/20 plus years, assuming quality workmanship (i have an excellent renderer) and also it will have Dulux exterior paint.

I'm more looking for confirmation on method - dormers already built, as timber stud cheeks with 18mm sheathing ply over (so too late for cement board) then quality breathable roofing membrane over that. I see comments about putting 25mm battens under EML to stop thermal bridging / create a vent gap. I could do this but suspect possibly an overkill, so am tempted to make do with using say 5 or 10mm nylon? spacers behind the EML that I'll screw through. Using SS screws at regular 6 inch intervals with prob a small SS washer to grab the mesh... not too big or may stop render adhering.
Also a 25mm void would surely require another solid ply/similar board to render against... not going to fill a 25mm gap with render scratch coat before it even reaches the EML.

I guess the beads will be SS anyway as exposed.

Any pragmatic comments welcome please!
Cheers
 

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jmoss5

Active Member
def batons . It’s going to crack any road . Render and timber not compatible in my opinion whatever precautions are taken to counter the inevitable movement . Good luck .
 
def batons . It’s going to crack any road . Render and timber not compatible in my opinion whatever precautions are taken to counter the inevitable movement . Good luck .
Ok thanks for the tip jmoss5. Sorry to be thick, but how do you stop the render going through the EML and filling the void between the battens? If it does fill the void and touch the sheathing ply (or the roofing membrane over it) then it destroys the point of this.
Surely the EML isn't enough to hold the base coat without having a surface immediately behind.
Other snag is as per the pic, these are gabled dormers and the front fascia only has a narrow gap of soffit (circa 2 inch) from the ply face - not sure i'd have room for the battens build up. Would be daft to only batten the sides, the front is the most visible bit if it cracks. Guess i could use thin 13x38mm battens.
Am I missing the point somewhere?
If you can explain by reply or send links to explanations / typical details that would be great...
cheers..
 
Thinking about it... my brother had identical dormers built about 4 years ago. Checking back on the site pics, he didn't have any battens on the sheathing ply, in fact (questionably) he didn't even have membrane, just ply, mesh and render. His dormers look totally fine 4 years later... surely any issues would've shown by now... I wonder if we're over egging this?
 
Hi Andy, thanks but you're jumping to conclusions.
Username is tongue in cheek.
I like to do things properly but unfortunately don't have bottomless pockets.
Defo not a £30k kitchen - half that if i'm lucky.
If money was no object it'd be an easy decision to always go for a better spec.
In my position I'd never afford to finish the project.
When something costs 5x as much you need a sound argument for it, more than just "SS is better and galv might rust".
We're talking about lath here which is fully covered, not exposed beads which will be SS.
There has to be balanced body of evidence out there even if anecdotal.
Any actual experience people have of whether galv really does rust / expected life span in normal circs would be appreciated.
 

smoother09

Well-Known Member
So you'll happily spend 30k on the kitchen but shy away from an extra £400 for SS riblath? You sound like just the sort of person I don't want to work for.
Nice apt user name.
Your right there f**k**g penny pinching on the exterior performance of the house! Some people are just dumb ass's!
 

essexandy

The Lake Governor
Hi Andy, thanks but you're jumping to conclusions.
Username is tongue in cheek.
I like to do things properly but unfortunately don't have bottomless pockets.
Defo not a £30k kitchen - half that if i'm lucky.
If money was no object it'd be an easy decision to always go for a better spec.
In my position I'd never afford to finish the project.
When something costs 5x as much you need a sound argument for it, more than just "SS is better and galv might rust".
We're talking about lath here which is fully covered, not exposed beads which will be SS.
There has to be balanced body of evidence out there even if anecdotal.
Any actual experience people have of whether galv really does rust / expected life span in normal circs would be appreciated.
Ok, the last outside render we did where we were removing and replacing, there was just one smallish projection of a timber construction. Galvanised EML onto battens fixed to building paper covered ply. The two side elevations were only rusty in places, the back, well it's a miracle it hadn't fallen of and killed someone. Rusted to hell.
Apparently less than twenty years old.
Replaced with SS riblath, I'll be long gone before there's anything issues with that.
 
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Ok, the last outside render we did where we were removing and replacing, there was just one smallish projection of a timber construction. Galvanised EML onto battens fixed to building paper covered ply. The two side elevations were only rusty in places, the back, well it's a miracle it hadn't fallen of and killed someone. Rusted to hell.
Apparently less than twenty years old.
Replaced with SS riblath, I'll be long gone before there's anything issues with that.
Ok fair point. Don't know the whole story though - if it rusted because the render failed and let moisture in (due to poor workmanship / paint going). Or regardless of this, can galv rust inside just from the moisture within the render.
Beads, different matter, they're exposed...
 

martinemj

Well-Known Member
Got job I've recently quoted for ...customer removing exp m lath which was fixed over brick ?
Completely rusted....render 25mm thick just hanging on ...fixings rusted too....
Worse still layer of dpm going up to top of wall.......wall was about 3m high ...one storey extension
 
ok guys you scared me, getting SS EML (not galv), managed to get for £25 ex VAT next day.
Ok noted comments re carrier board, anyway my renderer said ply/membrane/EML is good, he's a perfectionist and i've seen his work a few years down the line so I'm happy to stick with that this time.
Cheers all.
 

essexandy

The Lake Governor
ok guys you scared me, getting SS EML (not galv), managed to get for £25 ex VAT next day.
Ok noted comments re carrier board, anyway my renderer said ply/membrane/EML is good, he's a perfectionist and i've seen his work a few years down the line so I'm happy to stick with that this time.
Cheers all.
EML definitely needs to go on battens not straight onto membrane on ply. If he says otherwise he's no perfectionist trust me.
 

malc

TPF Special Forces
Got job I've recently quoted for ...customer removing exp m lath which was fixed over brick ?
Completely rusted....render 25mm thick just hanging on ...fixings rusted too....
Worse still layer of dpm going up to top of wall.......wall was about 3m high ...one storey extension

the early EML was black matt, galvanised was the 'improved' version.
 
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