Internal sand and cement float and set

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bof said:
I don't devil float , I use neat sharp , leaves a course open surface
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malc said:
i always devil float mine, but a lot of plasterers now float up smooth they say that multi keys to plasterboard . therefore why do you want to put a load of lines which will slow your skimming down ?
we where sharing a site with a gang from Southend,who floated up smooth, we floated a lot quicker then them but they came back on the skimming. overall about the same areas and same time.
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Anyone who thinks that way Malc shows a serious lack of understanding of the trade and has served no time as an apprentice or even some form of learning from proper spreads .IMO............just saying
 
malc said:
i find that i can float quicker then i can dot and dab.
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I loved floating s/c it's the mixing and lugging upstairs that's the drawback , working on refurbs it's not common to have a tip of sand outside the front door , dab simplifies things
 
beader said:
Anyone who thinks that way Malc shows a serious lack of understanding of the trade and has served no time as an apprentice or even some form of learning from proper spreads .IMO............just saying
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i know what you are saying .when i was an apprentice every wall was devil floated as it was needed for sirapite. they are saying that multi has better adhesion therefore no need to devil.
 
malc said:
i know what you are saying .when i was an apprentice every wall was devil floated as it was needed for sirapite. they are saying that multi has better adhesion therefore no need to devil.
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My dad devil floated but I don't think it's necessary on sharp , the surface is covered in plenty of pores , soft sand I can understand as the surface is smooth with no grab but I won't use it
 
I like a devil scratch. Run the float over and press the backing coat it in a bit, knock off any small high spots and get the key.
 
bof said:
My dad devil floated but I don't think it's necessary on sharp , the surface is covered in plenty of pores , soft sand I can understand as the surface is smooth with no grab but I won't use it
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Cornelius said:
I like a devil scratch. Run the float over and press the backing coat it in a bit, knock off any small high spots and get the key.
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they are still putting a float over the wall but no scratch.
 
malc said:
they are still putting a float over the wall but no scratch.
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That’s weird isn’t it? Go to the effort of putting a float on it but not key the surface? Obviously they don’t like the scratch in the surface taking more plaster to skim over.
 
malc said:
i know what you are saying .when i was an apprentice every wall was devil floated as it was needed for sirapite. they are saying that multi has better adhesion therefore no need to devil.
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then they are wrong but i will except i am wrong if @BritishGypsum would like to comment. who is at fault if the skim coat shells off,will bad plasterers just blame the muti and not there lack of knowledge and skill.
 
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malc said:
British gypsum don't recognise sand and cement as an acceptable backing coat. it needs to be the complete British gypsum system
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they do if they recommend to use board finish on it . They class it as a low suction background.
 
I always add 1 sachet of Entrainit to each mix, 1:5 float in one application, straightedge horizontal then vertical, fill in any hollows, edge again then when flat & plumb leave until firm then I cut in the wall/ceiling function to make it sharpe then I devil-up, then run my trowel over the wall to lay down any snots, leave it for about 5 days then skim. I then move back to the ceilings and scrim the ceiling/wall junction and set the lids. I’ll float S&C all day and devil-up at last load an hour before knocking off. If the floating has dried out I just spray with water to control suction. :)
 

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Love a sand and cement toss up
Better than a sponge post lol
 
It's still mostly sand and cement and skim in Ireland, some sites use hardwall but it works out more expensive
Very rare for it not to be skimmed the next day and never have any trouble with it
Put a nice drop of waterproofer in the mix to make it nice for floating and no lime
 
essexandy said:
So hardly anyone gives a f**k about shrinkage/curing times, no one in the history of plastering has suffered any delamination, and yet there are hundreds, nay, thousands of houses out there with shelled skimming.
Something's not adding up.
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It's just like the great mystery of skimming dry PVA lol
 
malc said:
i always devil float mine, but a lot of plasterers now float up smooth they say that multi keys to plasterboard . therefore why do you want to put a load of lines which will slow your skimming down ?
we where sharing a site with a gang from Southend,who floated up smooth, we floated a lot quicker then them but they came back on the skimming. overall about the same areas and same time.
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Don’t you find that a lot of domestics where the top coat has blown is down to no key? We quite often do it seems the walls were devilled while wet which just closed it in and didnt scratch it, then later the top coat comes off. I was always taught to scour my floating well
 
Mouldyoldspudgun said:
Don’t you find that a lot of domestics where the top coat has blown is down to no key? We quite often do it seems the walls were devilled while wet which just closed it in and didnt scratch it, then later the top coat comes off. I was always taught to scour my floating well
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Rule off , the large grits scour the surface , no need to devil float as it just closed it all back up , leave till well firm and gentle float to just press high spot grains in
More all over surface grab IMO
 
bof said:
Rule off , the large grits scour the surface , no need to devil float as it just closed it all back up , leave till well firm and gentle float to just press high spot grains in
More all over surface grab IMO
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We just give it a good scouring with a devil float not when it’s wet as that’s when it closes in plus we use screws and not thin arsed nails that push back out over time also use a plywood float rather than plastic
 
Mouldyoldspudgun said:
We just give it a good scouring with a devil float not when it’s wet as that’s when it closes in plus we use screws and not thin arsed nails that push back out over time also use a plywood float rather than plastic
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I think it's the timing causing the issue ( coupled with too small and regular grit size ) , as you say , people are closing in the surface when wet and relying on the devil lines , the other areas between are not a good bond surface
 
Mouldyoldspudgun said:
Don’t you find that a lot of domestics where the top coat has blown is down to no key? We quite often do it seems the walls were devilled while wet which just closed it in and didnt scratch it, then later the top coat comes off. I was always taught to scour my floating well
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Very rare thing me disagreeing with you me old mate!
I've seen loads of shelled finish where there has been a really deep scratch. If the floating coat is still shrinking at the time it's skimmed it will be shelled to some degree or other. Personally I use a very, very light scratch.
Choosing sand is, IMO, the most important thing to do when floating with s&c. The more silt content, the more shrinkage you'll get. Even with a good sand you'll get 2-4mm of shrinkage at 16mm floating thickness.
 
essexandy said:
Very rare thing me disagreeing with you me old mate!
I've seen loads of shelled finish where there has been a really deep scratch. If the floating coat is still shrinking at the time it's skimmed it will be shelled to some degree or other. Personally I use a very, very light scratch.
Choosing sand is, IMO, the most important thing to do when floating with s&c. The more silt content, the more shrinkage you'll get. Even with a good sand you'll get 2-4mm of shrinkage at 16mm floating thickness.
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We always use double washed but it doesn’t seem as good as it used to be leaves a lot more colour on your hand when you squeeze the sand than it used to. I was taught to scratch well on any floated surface, I guess it depends on who taught you and most importantly wether it works or not. I must say I know how young Jessica feels now with you disagreeing
 
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