Is this key good enough on S&C

Lastlaff said:
Okay, this helps with the diagnosis. So in the first photo it does look like it was just finished in skim (with no Bonding/Hardwall before the skim). The back of the skim does have a slight indent where the skim has been pressed into the S&C key (but, the key was still not good enough). If the floating coat is not consolidated with a devil float correctly the skim will not 'bond' together and any decent experienced spread would now this. The S&C coat doesn't look to have been straightened/ruled off to a decent floating coat finish. The sand & cement looks to be a 'builders sand' or similar sand....crap IMO for plastering.
When you scratch your finger nail over the skim finish does it seem powdery? Or is it tough/strong?
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Thanks for responding again - it does seem strong but if I run my finger over it there is a slight powdery residue on it when I pull it away

I can't go through going back to brick again it's just too messy - think I'll just have to get them to take the skim off blue grit reskim and hope for the best
 
Lastlaff said:
Okay, this helps with the diagnosis. So in the first photo it does look like it was just finished in skim (with no Bonding/Hardwall before the skim). The back of the skim does have a slight indent where the skim has been pressed into the S&C key (but, the key was still not good enough). If the floating coat is not consolidated with a devil float correctly the skim will not 'bond' together and any decent experienced spread would now this. The S&C coat doesn't look to have been straightened/ruled off to a decent floating coat finish. The sand & cement looks to be a 'builders sand' or similar sand....crap IMO for plastering.
When you scratch your finger nail over the skim finish does it seem powdery? Or is it tough/strong?
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Hi mate it or very powdery just rubbed my hands over it and the top surface rubs off and leaves a powder on my hand and the floor I take it that's bad? Can that be resolved??? Also if I run a Stanley knife over it it score up fairly easy
 
If the skim is powdery then the S&C has sucked some of the moisture out of the skim before it has had time for the chemical reaction (the setting action of the plaster). The degree and loss of strength of the plaster due to this action leaves the finish coat in a de-bonded state I.e. cracking and hollow.
If you bluegrit the S&C , make sure it is dust free and there isn't fierce suction....bluegrit is usually for low suction background and needs time to dry.
Good luck with it.
 
Daveo82 said:
View attachment 16511 Hi recently had a room back to brick and S&C now a month later there are lots of cracks and hollow patches - when hacked off there are no cracks in S&C only skim is the key good enough? Any other reasons this could have happened???
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Looks like dri coat to me with bonding or hardwall on top (to thick to be skim) , them lines ain't deep enough neither
 
You could just strip it and 2 coats of pva and then skim? Just like an overskim.... you just need to bond it to the base coat. Sand and cement looks too closed in (possibly steel troweled and that weird scarifier that's not deep enough and I've never seen used before) should of been devil floated in whatever direction would of worked. If you pre grit just prime it with diluted sbr/pva let dry then grit and then skim.
 
Best key of the lot,the back of the yard brush. I can't tolerate the nails in the float method.
 

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Floating coat devilled up then laid down with a trowel. I do it this way whether it's S&C or plaster....it also helps to flatten the background.
In fact, I do this on my external S&C scratch coat before I comb it - helps with wobbly render in sunlight.
Is this key good enough on S&C
 
Hey buddy,it's definitely a key with a suction problem,if they have hardwalled/bonded and skimmed the next day without pva the suction will be to great rendering the gauge useless,as with s&c if the wall is HOT the same will happen.the key it definitely not good and a devil float is the way forward here.unlucky for you the finish needs to come off I do think blue grit will work but I possibly would get the grinder out and give you some extra key but there may be a need to straighten the wall out before re-skim in order not to put a thicker than normal coat bk on ,hope this helps.
 
If I saw anyone using a brush on a floating coat prior to skimming, tools would be in the van soon after...


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Hey just a thought,is it actually dry wall over s&c with waterproofed in,this could repel each other especially if damp still? Any thoughts on that?
 
Way tighter key altogether. No shiny floated areas missed.We would do the same to give bonding a key prior to skimming. What's the problem with the brush BigK....?
 
solway said:
Way tighter key altogether. No shiny floated areas missed.We would do the same to give bonding a key prior to skimming. What's the problem with the brush BigK....?
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Its a s**t key for any finish to go over, whether render or skim there is not much to key too, with more chance of shelling or cracking.
 
Flynn is bang on, also skim on way deeper than necessary or needed, love to know how flat the wall is after you've gone over it with a brush head!!


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Try it before ye knock it lads. I've tried both ways and the brush is a thousand times better. Ye're disagreeing with the method but still asking questions about it.....
 
Only time I've seen it done was by a gang that would go over topcoat with yard broom prior to tyrolean to save time floating up. Never seen it done as a scratch, i was taught deep and wavy, what does @Rigsby think?
 
Only time I have seen a stiff brush used to create a key is in Ireland. Quite common over ther I have been told.
 
Your not doing it right so if it ends up rough after. Maybe you just don't have the "hands" to get it 100% to skim onto. The wall is ruled and floated plumb and to give the perfect key for skim let the brush fall gently between your hands. If you have to put force on the wall to get a key it's gone too far so it's all about timing and "soft hands". Nails in a float is the "quick townie way"...[emoji6]. Seriously iv never seen skim come away from it but I have on numerous occasions seen it come off in sheets from your way... I ain't trying to WIN this conversation I'm just giving my point of view. Each to their own but if I saw 1 of my men with nails in their float I'd tell them put their tools in the van and find a job elsewhere [emoji106]
 
It takes more time and effort this way beader. Dumbing down the trade.....WTF come on with me for a few days. You do it your way and I'll do it mine,we'll see which is the straighter wall with the better key. It's not just brushed to skimp on floating
 
What do you guys float over? Nearly all extensions are on lightweight blocks inside.... at least in my world. Absolutely no chance of straightening, floating and brushing before it pulls in. That's with dampening the f**k**s down.
 
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