Here comes the science bit...

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bigsegs

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just to follow on from gary b's knowledgable explanation of multi vs board...
it got me wondering what exactly (chemically) is the difference and why does it matter,
gary i noticed u mentioned using lime putty to hold off finish...
bod i noticed u mentioned using lime in render sent it off quick...
thing is...put chalk in an oven for 12 hours on a high heat, you get lime...mix said lime with water and it gets hot, very hot...
so...youd expect a limey mix to go off like grease bloody lightning yes??
but it doesnt...
wtf??
got me bit of gen off some science thing btw like how do they do it or somesuch..
and the lime putty thing off some website that specialises in it..chemical company, apparently the ONLY difference between hydrated lime and lime putty is the amount of water in it...
anyone know the chemical make up of the different finishes and what reactions happen??
yeh, i know, i think to much but blame gary b...he started it.. :D
 
When i first started there was only board finish and carlite finish, most plastering was done with board, and carlite finish was mainly used on roughing, but not sand and cement that was done in board, and the bags were bloody huge, as for the chemical formula between them its usualy a question you get from a customer, when your half way through the job you think, why the bloody hell i take this job, I knew from when i priced it up a week ago he was gonna be a nightmare. ;D What ever happened to carlite finish now thats a mystery?
 
I've got a bag of carlite in my shed..... I think it might have gone off tho, nearly broke my toe on it few weeks ago! ;D
 
bigsegs................ :(............ I worry.............I truly do ;)
 
yes yes i know i can be an anorak of almighty proportions its just that i like to know and understand the stuff i work with...dont they teach all this stuff on these courses then?? as in this is plaster...you dont need to know how it works, this is a trowel, you put the plaster on the wall with a trowel...now, theres a wall..go to it...ta for the fee...
ill give you a good example...
when i used to fit windows, you'd get toughened units exploding for no particular reason, annealed units cracking at 5 in the morning, again for no reason...
bit of research and its all down to nickel sulphide inclusions, and molecular sieve absorbing nitrogen...when explained to the customer its the manufacturer whos at fault, not me or my company, even when the manufacturer was all out trying to make us look stupid, faced with the evidence they pay up, replace the units and the customer thinks the sun shines out of my arse...
anyone know of any lit on the net explaining it all anorak style for nobs like me?? cant find sod all on british gypsum or the like...
 
Bod maybe I was a spooty 16 yr old kid but those bags were as bloody big as me LOL, the youth of today dont know just how lucky they are.

Well Bigsegs what can I say? I teach on them there courses and no they don't teach you the chemical differnce. I admire your deep searching and questioning mind my friend but I would like you to remove your anorak (as you put it) and ask why? LOL
 
In all honesty bigsegs I envy you the time to research it.
My thirst for knowledge extends to what I need to know.
For instance I need to know that if I put finish on dry cement it'll suck the water out and crack and how to recognise it and stop it.
What I don't need to know is the capilliary action involved in drawing the water and each strata's need to find a balance directly equating to it's density and how atmospherics and temperature affect all of these factors.
Having said that I like that I do know it.
I just wish I had the time to learn it all.
Good luck to you m8.
:)
 
I dont know if its just me, but do any one think that BG change there mix for summer and winter, with there sale by dates an all, I have noticed that during the season change the skim acts a little different, in the begining of winter skim seems to take ages to set and later winter it sets normal time then early summer spring the sets seem to start pulling in alot faster then full on summer the mixes seem to not pull in so fast even though they should pull in realy fast (this is only subjected to plasterboard) It might be just different batches? as have had skim set realy fast when its sale by date is up, and also had it go the other way where it dont set and goes all spongey with the sale by date gone.
 
well...im back from my 'how not to fix a laptop' experience and have learnt absolutely sod all about plastering since then...
i do however have a strange experience to add to my already impressive list of strange experiences..
did an over skim ceiling for a bloke, artex, silk paint. scraped off the high spots, gave it a thin pva which dried like fook..so i gave it another thicker (3/4:1), tacky then had it, maybe 14 square.
rads off, heating off, 3 months left on plaster (checked), bone dry got that morning...
went off like lightning, had to chase it to flatten 1st, fresh mix 2nd, same again...
went back on monday theres little tiny hairline cracks all over, not crazed, just here and there...solid artex underneath...blokes going 'it is a warm house this y'know' and he was right it was bloody hot in there when i skimmed it and still was, even though it was peeing down...
so i do his kitchen and hallway together, bout 12 square, not a lot..
exactly the same thing happened...
it was new plaster that morning too....
buggered if i know...very hot in there though, heating off again...dunno where the heat was comin from but he did mention having a full 300mm of loft insulation (bungalow btw)
maybe it was me generating the heat having to chase the bloody stuff round the ceiling...

anyway bod, what u make of this....
in winter the stuff takes forever to go off yes? so you get used to plodding round waiting for it to go off
then the hot weather comes and you find you have to run round like an idiot...
but then you get used to it and it becomes the norm....until winter comes again...
then it feels like theres something wrong with the plaster cos u been running round for the past few months chasing it...
then u get used to it again...
then of course summer comes and the process repeats itself...

if i knew the answers to all this id be able to explain to em what went wrong, or even prepare em for it instead of standing there like an idiot goin 'well its just too warm/cold innit'
think i might write to my mp...or maybe the chairman of british gypsum, maybe even osama bin laden, he seems to know his chemicals.... :-[

p.s. i remember someone once told me that board finish was sharp when looked at under a microscope and thats why they called it thistle??? not sure if he was winding me up or not...
 
hello mate ive seen a lad chuck nine buckets on in one set after being plastering 3 years ( i witnessed it myself) it was fookin cold mind but when he went upstairs in the same unit no glass was in and thats the first time ive seen a labourer trowel up 3 buckets after working with him for two weeks on ha ha sorry deano
looked mint though ;)
 
well 9 buckets is a lot but i suppose it depends on your bucket (mine holds about a bag and a half)..
i had a 20 metre ceiling on last jan and went and got a sandwich, ate it, then went and got a paper, read it then troweled it flat, mixed up again and topped the ceiling and put 2 walls on with it, then mixed up again and put the iother two walls on all of em wet...took all bloody day but i ended up troweling the whole lot up in one go, easy as fook...on board with multi that btw..
strange how the slightest difference in temperature/humidity makes a massive difference in set time...just wish i knew the numbers, then rather than take 20 years to get a feel for it, you could teach someone with reasonable intelligence in 6 months...
 
BG do change their mix from summer to winter although they will never officially admit it. I was told this by a chemist who visited one of our sites once. Basically because of the colder weather they alter the amount of retarder in the mix so as to regulate the setting time.

But in October and March when the weather can be warm and cold it plays havoc with the lads on site cause the stuff is really hard to trowell as its setting and behaves like "toffee" was one word used to describe it lol. Also thats the changeover time between the winter and summer mix and the stuff dunt behave itself.
 
LOL ive not seen this for ages, I asked some smart arse on a different forum what was the formula for and what was the difference
Ca so4 2h20 and Ca so4 2h (half)2o funnily enough i never got a reply. This was drilled into us at college and at the time we all thought what was the point of knowing, little did i know i would be asking someone on a forum 20 years later. i always had visions of being asked this on who wants to be a millionare for the final question but heres dreaming.  ;D
 
i honestly used to think that 'fly ash' was cremated flies...couldnt think what else it could possibly be??
i think ill just have to hope that if i ever get asked 'whats in plaster then?' and i go '2CaS04.2H2O (heat)»»» 2(CaSO4).H2O + 3H2O' (just gotta work out how to pronounce it :D) theyre so impressed they just make me a cup of tea and give me a tip instead of asking 'so whats that mean then?' ;D
 
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