How do you know how much to mix?

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Steve28

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When plastering a large area, how do you know how much to mix for your first coat? Is it just experience or do you use the formula where you divide by 9 to help work it out? I've got a 17m2 artex ceiling to do tomorrow and was looking to mix about a bag and a half for my first mix, about right or not?
 
Yep , never heard of any mathmatical equations to work it out, just down to experience - Like Ian said, you're about right on a bag - bag and a half for a 4x4 ish ceiling , depends how thick you mix your first coat up
 
I always just take an educated guess mate. There is a mathematical way of working it out (cue Big Segs) but then plastering ain't always an exact science and it depends how thick the mix is etc. One thing for sure, always mix more than you need.....if you mix too little you're up a creek with no discernible paddle :o
 
One thing for sure, always mix more than you need.....if you mix too little you're up a creek with no discernible paddle  :o
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This almost happened to me the other day, have any of you's ever ran out of plaster? What would you do if this ever happened.
 
a bag should cover 9 sqm inc second coat including wastage , but as its an artex ceiling i'd be tempted to take 3 bags if youre not bonding it first
 
it depends on the atex mate i dont normally do three coats of skimming i'd rather use bonding/dirty water if it's heavy, but even a slight stipple will use up more kit and the 9 sqm per bag is based on skimming plasterboard so i'd take an extra bag as insurance, try to gauge youre mixes accurately though because you might get away with using two bags ...............i hate opening another bag just for one handfull!
 
if you do fall short on your mix im sure that would not be a vast amount ,if you do, mix it up straight away in the same bucket that you have used for the first mix,if i was you i would put a tight coat on the artex then straight away flatten of using another coat,wait for that to start going,flatten, then apply your final coat
 
lol...my 'mathematical formula' goes a bit like this...
look at how big the 'ceiling / area' is...
if ive got walls/reveals/another ceiling... prep em first...
mix up a bag and a half..
lay it on till i run out of mix... (completing all 'areas' though)
trowel it up...
mix about half as much again..
top it..
trowel it up etc..
if its a small area only experience is gonna tell u where abouts in your bucket to fill it depending on how level/flat your background is before you start and whether you got beads/reveals on or not...
like nicksey says, opening a bag for a handful is a pain but always have an extra one anyway just in case, if im gonna run out of mix i just top it thinner and move a bit quicker..
or to put it another way...
the amount of plaster left in the bucket once finished (or not finished whichever way you get it wrong) is directly proportional to the experience of the plasterer...
;)
 
what i mean by putting on a tight coat is virtually get your first coat on thiner so it has hardly any lines in it and get it write in on that artex,dont know how to explain it much better,anybody else
 
Alright Steve

This is how i do it : 17 m2 Divide by 9 = 1.8 Bags of Finish for the whole area.

1.8 Divided by 3 = ( 0.6 of a bag )

0.6 x 2 = ( 1.2 bags )

1.2 Bags will do your first coat, Then 0.6 of a bag will lay in your second coat.

To make life easier and cover your arse round the 1.8 bags of to 2 bags for the job ( knock up a bag and a half 1st coat then top it with half a bag )

Job done hope this helps mate.

Mush
 
tight coat, thin coat, measly coat, just enough to do the job coat :D
what i do with artex is make sure my first coat is nice and thick (mixed and applied, finish not bonding) then i let it pull in so when i flatten it, it goes well.. flat and the important bit is the artex is ALL covered.. no little white bits showing... then i just top it as normal....
a tight coat of bonding would help i suppose if the artex is ridiculously thick... like when someones put it on with a shovel and just left it to set...
always pays to think about what exactly the artex is laid onto though.. if its old lath and loose plaster and thick artex, laying another 5- 8 mil over that might just have it on the floor, or at least wont do it much good... better to overboard or better still drop it and reboard..
finish plaster is 25kg per 10m2 @ 2mm thickness...
or 2.5kg per metre...
or roughly 250 grams per foot...
times that by 4 for 8mm thickness...
and thats around a kg per foot square...
glue a foot square peice of plasterboard to a lath and plaster ceiling and hang a large bag of sugar from it...
all over the ceiling...
im bored now... :-[
 
We normally go by 10m2 per bag so if ceilings 17m2 and its artex, i like it thick on first coat to get plenty on to cover the artex, i'd do about 2 bags (20m2) to cover artex then half again for second coat (1 bag). This makes sure all the artex is covered and you've nothing to worry about. No matter how heavy the artex is i've never bonded it out first, thats 3 coats and whats the point when you can do it in 2! Artex is one thing it won't go far on board its a lot diffrent.

Best advise always take more multi than you will need, that way you won't run out and always mix slighty more than you need as its easier to clean out bucket once you're finished rather than trying to knock up more mix when you're already chasing your tail!
 
We normally go by 10m2 per bag so if ceilings 17m2 and its artex, i like it thick on first coat to get plenty on to cover the artex, i'd do about 2 bags (20m2) to cover artex then half again for second coat (1 bag). This makes sure all the artex is covered and you've nothing to worry about. No matter how heavy the artex is i've never bonded it out first, thats 3 coats and whats the point when you can do it in 2! Artex is one thing it won't go far on board its a lot diffrent.

Best advise always take more multi than you will need, that way you won't run out and always mix slighty more than you need as its easier to clean out bucket once you're finished rather than trying to knock up more mix when you're already chasing your tail!
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plaster shrinks when it dries mate and you won't be going over a coat of multi when it's rock hard because it wont adhere, if you bear in mind a coat of plaster does go on 2-3 mm you could get this deviance even on a slight stipple
if you use a tight coat of bonding ...which you should especially if the artex is a heavy bark effect etc at least the plaster has cured you'll get a normal suction from the backing coat, if you lay a second coat onto a green backing coat you'll get indifferent suction because it's not a flat background and it'll pull in together leaving hollows
 
always fined with artex overskimming which i would rarther not do on ceilings,better with1 tight coat then a second coat straight on that flatten,then final coat  always turns out best but i suppose we all have our own ways
 
when over skimming artex i tend to put a couple of handfuls of board adhesive, it then lets you lay it on that little bit thicker than normal. Then second coat as usual without the adhesive. works for me
 
We normally go by 10m2 per bag so if ceilings 17m2 and its artex, i like it thick on first coat to get plenty on to cover the artex, i'd do about 2 bags (20m2) to cover artex then half again for second coat (1 bag). This makes sure all the artex is covered and you've nothing to worry about. No matter how heavy the artex is i've never bonded it out first, thats 3 coats and whats the point when you can do it in 2! Artex is one thing it won't go far on board its a lot diffrent.

Best advise always take more multi than you will need, that way you won't run out and always mix slighty more than you need as its easier to clean out bucket once you're finished rather than trying to knock up more mix when you're already chasing your tail!
Click to expand...
plaster shrinks when it dries mate and you won't be going over a coat of multi when it's rock hard because it wont adhere, if you bear in mind a coat of plaster does go on 2-3 mm you could get this deviance even on a slight stipple
if you use a tight coat of bonding ...which you should especially if the artex is a heavy bark effect etc at least the plaster has cured you'll get a normal suction from the backing coat, if you lay a second coat onto a green backing coat you'll get indifferent suction because it's not a flat background and it'll pull in together leaving hollows
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very good point is this...
maybe im just lazy but the one thing i hate having to do is bonding followed by skim, too many people will just follow the 2 coats of skim method, me included.. i only bond out something if i absolutely have to... like when theres big hollows etc... 99 percent of the time with artex its a thick suction coat, pull in and top it and to be honest, the amount of houses ive been involved/priced for and done the whole job as complete redevelopments, the only problems i get are plaster delamination due to dodgy chalky paint under another 2 coats of whatever... or too little suction and it ripples like a fat bird... or even two coat pva dont kill it.. when its painted its never bang on but completely saleable and the walls are always a thousand times better for two coats of multi... end of the day its an overskim... if its perfection they want with very little chance of future problems its drop it and reboard...
incidentaly, this weeks job... reskim whole house for a property developer....
we'll finish skimming tomorrow, the kitchen was done 1st hit monday, still aint dry, and they got a painter in 12 hours after us...
paints lookin ok so far on what has been reboarded, even some that hasnt hes been cracking on with...
we've had silk paint over distemper, the skims soaked into the cracks in the silk, loosened the distemper, had 1/3rd of a ceiling down today... and the f'cker always waits till your on your second trowel after toppin it...
they get what they wanna pay for, what they though they could get away with turns out they couldnt...
gypbond was king this week....
converted my mate too... old school plasterer...
ah well, all plasterers go to heaven, property developers end up in hell tied to stakes in mounds of burning 50 pound notes  ;D
plastering can be so fickle sometimes...
lets all offer up prayers to the gods of suction and adhesion and get em to leave us alone for a bit...  ::)
 
Nicksy

Don't know if you picked me up wrong but i lay on first thick coat of multi and when i'm flattening it out the boy is knocking up second coat. Always top first coat with plenty of time to spare! If you don't as you say it won't take , been there and done that its no fun!
 
ok mate i'd just be a bit worried that because the first coat can shrink into the hollows it will pull the second coat into it ............
 
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