internal sand/cement with lime.

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johniosaif

johniosaif

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We got a job to do in an expensive new block, they wanted the plastering done in sand/cement. the walls were smooth concrete and solid block. They had an old plasterer do the first two flats and gave us three on price. I suggested scudding the walls with sand and cement slurry with pva in it.They wanted the sand to be a mix of building and plastering at 50 50. We scudded and then scratched with first coat four to one sand cement with two shovels of lime in each mix, the second coat was a five to one mix, we then skimmed with multi.Each flat took about seven tonnes of sand/cement. When drying out the walls were showing signs of salts*efferesence* The salts caused some of the plaster to be pitted, the builder said it was the fault of us putting the lime in and that was where the white stuff was coming out was from. I tried to explain it was dampness trapped in the blockwork which got wet during the building works..They never heard of such a thing.what can you say then. I did get paid thankfully but I think they were fairly amateurish.. Your thoughts please..
 
johniosaif said:
bit lost on the ? andy. I expect we all float and then set, sorry if I am missing your real question
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When I say a second coat, it basically goes on straight after the first so we scratch stick beads then bang on the second, skimming the next day..
 
johniosaif said:
When I say a second coat, it basically goes on straight after the first so we scratch stick beads then bang on the second, skimming the next day..
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Sorry mate but that goes against all "good practice" IMHO.
If you don't get a call back regarding more serious problems then you've been very very lucky.
 
So lime render, has the efferesence come out on just the areas which were blockwork ? or where the walls were smooth conc ?
 
essexandy said:
Sorry mate but that goes against all "good practice" IMHO.
If you don't get a call back regarding more serious problems then you've been very very lucky.
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I expect you mean debonding or blown areas andy, perhaps I have explained myself wrong or indeed have done it wrong, can you tell me how you would have done it that is different.?.Thanks
 
i would have just pva the smooth concrete walls and skim. cement and sand floating went out with the ark!
 
malc said:
i would have just pva the smooth concrete walls and skim. cement and sand floating went out with the ark!
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They asked for sand/cement floating ,the walls were badly out of plumb, they did not want any hardwall or bonding used.
 
johniosaif said:
I expect you mean debonding or blown areas andy, perhaps I have explained myself wrong or indeed have done it wrong, can you tell me how you would have done it that is different.?.Thanks
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If the client has specified render, float and set then the first coat needs to cure before the float coat. And then the float coat needs to cure before skimming.
If on the other hand the client just wants it float & set using S&C then I'd have just beaded, applied any adhesive I thought necessary, put an 11mm float coat on, allowed this five days to cure and then skimmed as normal.
 
essexandy said:
If the client has specified render, float and set then the first coat needs to cure before the float coat. And then the float coat needs to cure before skimming.
If on the other hand the client just wants it float & set using S&C then I'd have just beaded, applied any adhesive I thought necessary, put an 11mm float coat on, allowed this five days to cure and then skimmed as normal.
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Funny I do not agree with this andy ,we never have five days to leave anything for.normally if we scud the day before,we then float,we let first coat pick up then apply second which we float in with a devil float, the next day is good for skimming in my opinion, sadly this time it was not due to hydroscopic salts but we had no way to know this.. Thanks for replying ,please accept that I disagree only on this time of five days..
 
johnio, i`m with Andy on this on, cement needs time to cure,if you had a whole flat to do why not float out everything and then skim later.If the client wants it quicker then tell em to get fooked, or use hardwall n set.

Malc it be old school, but imho its still the best way, and a builder i do bits for only floats with sand and cement, and it always comes out mint, if left to cure properly.
 
kebab king said:
johnio, i`m with Andy on this on, cement needs time to cure,if you had a whole flat to do why not float out everything and then skim later.If the client wants it quicker then tell em to get fooked, or use hardwall n set.

Malc it be old school, but imho its still the best way, and a builder i do bits for only floats with sand and cement, and it always comes out mint, if left to cure properly.
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It is something I will keep in mind but on most sites they want rooms finished for storage etc, it was a perfect flat for hardwall except for the fact the walls had got soaked during the building. Sand /cement was the way they wanted to go, there was no other problems other than the efferescence coming out in some places...
 
Everythings always needed in a hurry, why cant T***s listen to the people who know best, plasterer that is.Buidlers s are really thick or stupid these days, or just do not know any better.
 
With all due respect Johnio you can disagree about curing times but you're wrong. S&C will not have cured/shrunk overnight enough to make it suitable for skimming. I've seen many jobs where the skim coat sometimes looks fine but is standing there independent of the float coat and others where the skim has just fallen to the floor leaving the float coat as clean as a whistle. This is often referred to as the skim having failed but the truth is that the S&C just carried on shrinking back away from the set, ridgid skim coat.
Loads of spreads will say "I always skim the next day without a problem", but the truth is the problem just isn't always found until they've long gone. That still doesn't make it right, does it?
 
Lots of jobs that I do have designers,architects, surveyors,builders ,clients etc but no one ever asks the tradesman for an opinion, we become invisible to them, they have the jobs priced and do not want to hear of work that is essential in our opinion.ie ceilings need to be pulled down,new lintels needed ,blown plaster needs to be pulled off. the paint /distember/artex wont hold up..we are just to nod and smile until they tell us what we told them and agree they have had a great idea..
 
kebab king said:
Everythings always needed in a hurry, why cant T***s listen to the people who know best, plasterer that is.Buidlers s are really thick or stupid these days, or just do not know any better.
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To be honest mate most plasterers know no more than the builders, just think of some of the things that come up on here.
 
You will get to a point in life when you just tell em to fuckkk of, i have and cant be arsed to be fooked around by assholes like that.
 
johniosaif said:
Its not two coats as such, its one half put on all the way around ,then scratched and the second half put on...
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But the two coats are different strengths so it's not a monolithic coat, and the different strengths will cure at different rates.
 
essexandy said:
But the two coats are different strengths so it's not a monolithic coat, and the different strengths will cure at different rates.
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true, never looked at it that way ie different strengths, but honestly I have never had a problem with it either. I have never been asked or seen plasterers leaving it for a week to set prior to plastering ie skimming, possibly because of all the push and rush on sites. its just new to me thats all Andy..
 
essexandy said:
With all due respect Johnio you can disagree about curing times but you're wrong. S&C will not have cured/shrunk overnight enough to make it suitable for skimming. I've seen many jobs where the skim coat sometimes looks fine but is standing there independent of the float coat and others where the skim has just fallen to the floor leaving the float coat as clean as a whistle. This is often referred to as the skim having failed but the truth is that the S&C just carried on shrinking back away from the set, ridgid skim coat.
Loads of spreads will say "I always skim the next day without a problem", but the truth is the problem just isn't always found until they've long gone. That still doesn't make it right, does it?
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Obviously if it fails it is not right, but I have not had it fail and I have had the same clients for ten yrs and more, I will still bear in mind what you say when sand/cement a full flat out in future, but if I was to float one room I would still skim it the next day..
 
I used to work for a damp coursing firm years ago doing council houses, so we had to be in and out as they were usually occupied and as result were told to float up then skim the next day and i can tell you we had no end of problems with cracks etc .BUT i was young and easily led in those days and now i would never skim the next day but would leave it as long as possible (3-5 days). over the years have been to many jobs where the skim on a wall has been hollow and found it shelled off clean once you get behind it but the render has been fine, but this can also be because there was not enough key when rubbed up.
 
Thanks Beader, I think the cracks can also come about because of the strength of s/c mix in damp proofing and also sika as an admix makes it stronger and without any flexibility it can crack.A good floating with nails leaves a good bond also for the skim coat, ps lots of damp proofing is also skimmed the same day if its only a few metres..
 
You can't skim sand n cement the same day as the surface will not be firm enough to take it as the grains of sand come away (if that makes sence) and the skim just falls off ,its a disaster to even try it.
 
beader said:
You can't skim sand n cement the same day as the surface will not be firm enough to take it as the grains of sand come away (if that makes sence) and the skim just falls off ,its a disaster to even try it.
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I have seen it done by damp firms, even seen them putting in bonding in the render to speeed it up, damp proofers are the cowboys of our game generally speaking ie those that only do a metre high all their lives..
 
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