internal sand/cement with lime.

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essexandy said:
Exactly the same as when outside rendering, you always need to wet down the first coat more on the low suction backgrounds to get it to cure, don't you?
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I don't hose down my scratch like some do, that often. Occasionally when I think it's drying too quick I might.
 
Do you think it's because low suction backgrounds are generally more dense and so have a higher thermal mass. In other words they hold heat better and that gets transfered back to the fresh render applied?
 
DannyMac said:
Do you think it's because low suction backgrounds are generally more dense and so have a higher thermal mass. In other words they hold heat better and that gets transfered back to the fresh render applied?
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No as I said earlier I think it's because the water has all come out into the atmosphere and the S&C hasn't cured as well as it does on Celcons. If you use the same mix on both Celcons and concrete blocks and leave them to dry out the render on the concrete blocks won't to as hard as that on the Celcons, if just left to it's own devices.
 
essexandy said:
No as I said earlier I think it's because the water has all come out into the atmosphere and the S&C hasn't cured as well as it does on Celcons. If you use the same mix on both Celcons and concrete blocks and leave them to dry out the render on the concrete blocks won't to as hard as that on the Celcons, if just left to it's own devices.
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Hmmm, dunno. I'm not convinced, that doesn't sound quite right to me. The slower the scratch dries, the better it cures doesn't it?
 
DannyMac said:
I didn't know that. i haven't skimmed much S&C TBH.

Why do you think it works that way?
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sorry danny never asked why? thats just the way it is, if you skim a brick wall where the suction was highest the set would hang wet the longest. when the floating high suction you floated in two coats , [giving the wall one coat then follow up straight away with the second coat] to give yourself time to rule in.
 
Hi lads when i used to work with an old plasterer. he use to say to me never put building sand in plastering sand. as the salts mix and will come out in the skim coat. (efflorescence) notshore if this is true but he swore by it. and if i s and c render. i leave it 3 to 5 days then skim and never had a problem. hope this helps mate
 
hirst said:
Hi lads when i used to work with an old plasterer. he use to say to me never put building sand in plastering sand. as the salts mix and will come out in the skim coat. (efflorescence) notshore if this is true but he swore by it. and if i s and c render. i leave it 3 to 5 days then skim and never had a problem. hope this helps mate
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Thanks Hirst, lots of the stuff is hard to know to the exact point, we just work as we have been taught and learned over the years, but its good to still learn from guys on this forum even the condescending ones..
 
building sand has a high clay content and as the render dries so does the clay and we all know what happens to clay when it dries out, it cracks to buggery
 
jrplastering said:
building sand has a high clay content and as the render dries so does the clay and we all know what happens to clay when it dries out, it cracks to buggery
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some guys I believe use building sand to render celcon blocks internally. a big no no in my opinion
 
johniosaif said:
some guys I believe use building sand to render celcon blocks internally. a big no no in my opinion
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I've used building sand for internal work on Celcons for years (about 800 houses) although it's a fairly clean building sand. It's nicer to work with than "plastering sand".
 
you will love this years ago on S&C internal work we used to put fairy washing-up liquid in the mix as a plasticiser then skim with a plaster called surfite finish loverly stuff to work with ,and we never had a problem !!lol
 
not tried that sand andy ill have to give it a shot i know at least on of the big jobs we got on next year is all float and set if its sand and cement ill try it out.
gooner we used fairy for the same purpose 10 years ago when i started:RpS_thumbup:, was a cant trying to get the bubbles out of the mixer at the end of the day haha:RpS_lol:
 
essexandy said:
I've used building sand for internal work on Celcons for years (about 800 houses) although it's a fairly clean building sand. It's nicer to work with than "plastering sand".
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I always find it inclined to crack, I would of been too scared to use it, but If it is good enough ,had building sand delivered by mistake before and used up some of it but always afraid of come back and yet you done hundreds without any... every day a school day
 
johniosaif said:
I always find it inclined to crack, I would of been too scared to use it, but If it is good enough ,had building sand delivered by mistake before and used up some of it but always afraid of come back and yet you done hundreds without any... every day a school day
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I've got pits that are close to me that have sand I wouldn't touch with a barge pole Johnio, as you say they would probably shrink and crack. I think it's down to knowing the materials you're buying, I'm fussy with sand for plastering, rendering and screeding.
 
essexandy said:
I've got pits that are close to me that have sand I wouldn't touch with a barge pole Johnio, as you say they would probably shrink and crack. I think it's down to knowing the materials you're buying, I'm fussy with sand for plastering, rendering and screeding.
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Been in london and with the turndown in trade we are all over the place and good sand is like a good cafe as in hard to find. some of the stuff is like seaside sand..Doing mostly refurbs with a mix of materials and in different areas all over london it is difficult to get good stuff, why do the merchants have this crap, they must get negative feedback
 
But that's the problem Johnio, most spreads are such clueless twots that they don't know the sand is crap, the times I moaned about materials over the years and the suppliers say "no one else has mentioned it". Whether that's true or not I don't know.
 
I can hold my hands up and says I aint got a scooby doo what is good sand and what aint. All I knows is I dont use building sand for rendering. So what should I be looking for and avoiding when sourcing decent sand ??
 
Artisan998 said:
I can hold my hands up and says I aint got a scooby doo what is good sand and what aint. All I knows is I dont use building sand for rendering. So what should I be looking for and avoiding when sourcing decent sand ??
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Grab a handful of sand and hold it underwater and move your fingers around a little to let the water at it, if you can see loads of silt/loam coming out of it then don't use it. If you just get a little silt coming out then it'll be fine, assuming it's neither to coarse or to fine. This is only for internal work mind.
 
essexandy said:
Grab a handful of sand and hold it underwater and move your fingers around a little to let the water at it, if you can see loads of silt/loam coming out of it then don't use it. If you just get a little silt coming out then it'll be fine, assuming it's neither to coarse or to fine. This is only for internal work mind.
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and for external what else do you look for??
 
Sometimes had that sand that's full off the black tar, oily ****! Then it bleeds thru on the render:RpS_cursing:
 
essexandy said:
But that's the problem Johnio, most spreads are such clueless twots that they don't know the sand is crap, the times I moaned about materials over the years and the suppliers say "no one else has mentioned it". Whether that's true or not I don't know.
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they trades probably just go elsewhere,I deal with some merchants and buy everything from them except their sand.
 
Artisan998 said:
and for external what else do you look for??
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For external work it must be really clean and not to many little stones in it. For pattern work I like to use quite a fine sand but for plain rendering a courser sand is preferable. Just my opinion others will differ.
 
you must know what is the quality of your local sand pits.
i like a really sharpe sand, preferable white, for floor screeding so that it pumps and lays easy.
a sharpe sand, but finer then screed ,for rendering.
i would use a mixed 50/50 sharpe and soft sand for floating but have not floated in cement and sand for years.
 
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