plastering advice plz? anyone

[jwatson]

anyone know what amount of sand/cement i would need to render per m2.
i have a garden wall to do which needs SBR ing some dubbing out. then 4 to 1 scratch and 5 to 1 finish.

asked the plastering forum but not quite as many members as over here. was hoping someone could help.

obvs thanks will be given.

[whitebeam]

Is it new brick/block work or some old tat your rendering onto...

[jwatson]

still some old tat but brickwork on exterior garden wall. think the whole of blackpool held up by willpower alone

[whitebeam]

I work it out at a bag of sand per m2 then your'll know that will more than cover you....stick with a 4-1 for both coats but get a good grade of rendering sand, there is some real rubbish out there and don't use soft sand.

[ozboz]

Years ago we used to say 3-1 will cover 6 yards @ 1/2 inch, so i suppose translated 150 kg sand - 50 kg cement will do 6 m2 @ 12 mil for scratch coat, but as i remember it was always adviseable to go weaker on top coat, if you are going to use SBR then stipple/slurry coat may be required to help scratch coat bond to brick/blocks

[jwatson]

yeah told me at college top coat to be weaker to control suction, and stop top coat de-laminating scratch coat. forgot bout slurry

Years ago we used to say 3-1 will cover 6 yards @ 1/2 inch, so i suppose translated 150 kg sand - 50 kg cement will do 6 m2 @ 12 mil for scratch coat, but as i remember it was always adviseable to go weaker on top coat, if you are going to use SBR then stipple/slurry coat may be required to help scratch coat bond to brick/blocks

[paul78]

top coat always weaker than scratch, dont forget your waterproofer.

[***tony***]

Last time I did any rendering I added lime to the mix ?

[whitebeam]

You might even use some eml on the face of the wall which would require a stronger coat for the scratch coat...which would allow if any movement took place.

[ozboz]

Lime makes it 'fatty' and keeps it 'alive" bit like plasticiser, they used it a lot in victorian days, i remember working in some terraced houses in Oldham, the
internal brick work and plaster was what looked like black ash,lime and a tad of some binder, I believe in the earlier times there was some sort of hydraulic cement, very soft and absorbant, then portland came along,

[whitebeam]

They use hydraulic lime many moons ago..

[widler]

slurry coat with sbr and cement,not weak nice and strong or it will dust up.
you will have to do it on blackpool red brick(they most prob accy nori)even maybe give it a grind or screw and fix EML as well .
i always use 3-1 scrat and 4/5-1 top.
like white beam said,use a good grade sand,i can get washed waddington fell here,its fantastic for render(its grit sand but sieved)really binds togeather,never had a render crack in nearly 30 years,but thats with ALWAYS gauging with buckets,NEVER shovels.

ps id only use lime in the top coat,would make too much suction and would kill your top coat

[ozboz]

Yep, its very imteresting a lot of it is still there as testimomy to the craftsmen of their day

[Alan M]

hi there. i used to help my father plastering.
we skudded with 3-1 slurry coat. no plas. cover the whole wall.
then scratch with 4-1 then finish with 7-4-2 . and use waterprofer

[ozboz]

Is that 7sand 4 lime 2 portland ?

[Alan M]

sorry 7-2-1. 7 sand , 2 cement, 1 lime

[widler]

sorry 7-2-1. 7 sand , 2 cement, 1 lime

wouldn't that make it stronger than your scratch coat? thats like a 3 1/2 to 1 ,the lime would weaken it but still a lot of cement