Calculating Mix and Waterproofing it.

[Sharkskimsoup]

Guys,

I completed a plastering course a few years ago. I did nothing but render for the first half of the year and got fairly good at it. Trouble was that there was a huge mixer at the school and I just got barrow loads of lime/ sand as and when I needed it so I never really knew how to work out quantities.

Is there a way of calculating the quantities needed assuming I do a scratch coat and finish? I am going to order the delivery of sand soon. I hear you all talking about these new products that "replace the old methods" but I would feel more comfortable sticking to what I know.

Also, can anyone offer advice on a product I can put in my mix (and where to buy it) to slow the setting down and offer good waterproofing?

Many Thanks

[chancer]

havnt seen waterproofer in a spec for external rendering for years or are you talking internal damproofing,either way forget the lime if using w\p they dont get on,ratio of sand and cement will vary on the background,to slow the set use a retarder the greatest of which is a hose pipe,if you were tought to use w\p on all external render ask for your cash back youve been badly educated!
if i need to slow a set use pva the ordinary not w\p as a admix,up to half a tub to a bag of cement,that apllied to a damp scratch will give your granny enough time to float up!
25kg dry mix ie 4:1 s\c should give you around 2.5 to 3msq at 6 to 8mm deep.

[xl292005]

Hello, Ive just completed a level 1 C&G plastering and a 14 week render coarse at dudley college and i too was told to use a waterproofer. the practice plaster contains lime but thats as close as you get to it. Screw fix and toolstation do a 3in1 mix solution for render wich i have used and it does work but i keep hearing the same thing as chancer just said about the use of waterproofer/plasticiser instead of lime. i would love to learn more about the use of lime mixes and the more traidional ways of doing it. it seems that college coarses have got to get you through the units as fast as possible only completing about 10 out of 20 or so units available so there is tons of stuff you just dont learn, that is why i'm not going to spend money on a level 2.
i think i have drifted from the subject a little have'nt i but i got my moanin head on today

[Whitebeam]

If you use a scratch coat then a floating coat it will last quite a while before you can rub up