Cement rendering questions...

[AL_n]

I need to render (with sand & cement) 30 square metres of exterior blockwork.

I have done a little cement rendering in the past, but not much. Can anyone advise the best mix of sand, cement, and possibly lime and/or plasticiser that will give best workability?

How much I will need, for 30 sq mtrs?

Many thanks,

Al

[NT]

1:1:6 (lime, cement, sand, by volume)

You can calculate the volume. Density is around 2.2.

NT

[AL_n]

NT wrote in news: [e-mail]:

Thanks... Should it be sharp sand, or will any building sand do? (for optimum stickability, while wet.)

Sorry, I'm not familiar with the density factor; can you clarify?

I calculate the volume to be 0.5 cubic mtrs.

Can anyone tell me the volume of a 25kg bag of damp sand?

Thanks..

Al

[The Natural Philosopher]

that about 3:1 so .08 cu meters

What yer man is saying is that half a cu. meter of goodies is gonna be a shade over a ton = I'd buy a tonne and a half meself - of stuff.

Of which 1 tonne will be sand (I like sharp for render - nice rustic feel) and the rest a mixture of cement and possibly lime.

if you go for a 3:1 mix which is quite 'strong' you need something like

1/4 tonne of cement - that's ten 25kg bags - and about 5 bags of hydraulic lime, to give it a bit of plasticity.

That takes the total up to about 1.375 tonnes in all, which is probably what half a cu meter weighs.

HOWEVER bear in mind that 'tonne bags' are often only about 875kg or so..so you may find you need a bit more sand in the end.

get yourself a tonne bag of sand, and then buy the lime and cement as needed. Unless you think you can render that much in a couple of days.

at this time of year use a frost additive as well.

This is where a trade account and delivery from a builders merchant is worth considering.

[NT]

1 cc weighs around 2.2g. I wouldn't use 1:3, you want the render to fail when something moves, not the bricks. 1:1:6 is nothing like 1:3.

NT

[stuart noble]

I notice some very large Readymix silos on a building site near here and it says "lime mortar" on the outside. What's all that about? Can they be bricklaying with it?

[NT]

I've heard of mortars called lime than are cement based with some added lime, and thus behave nothing like genuine lime mortar. I don't know which the readymix one is, but given that bricklaying with real lime mortar is so problematic, odds are its cement with lime.

NT

[AL_n]

The Natural Philosopher wrote in news:jg66jd$or4$1 @news.albasani.net:

Very helpful - thanks. I'm thinking of more like a 5:1 mix. Thanks for the account suggestion; I do have an account at Jewsons, and I do remember them saying they deliver. That'll save some aggro...

Al

[AL_n]

NT wrote in news:1db91c33-64b0-45b1-98fd- [e-mail]:

I agree completely. 1:1:6 sounds about right for this job. Thanks.

Al

[The Natural Philosopher]

Well then get that tonne of sand and a few bags of whatever and some winter mix, and play around with ratios till it feels right.

This is not an ideal time of year for rendering.

It can take a couple of days to set. Mild and damp is best. Subzero is awful.

[AL_n]

The Natural Philosopher wrote in news:jg6pjb$3tr$5 @news.albasani.net:

I'm planning well ahead. Wild horses wouldn't drag me out there at this time of year. ;-)

Al

[Andrew Gabriel]

Much better if you can wait until no risk of frost.

Also, don't touch the surface for 6 weeks - it takes that long before it reaches full strength and it's easily marked before then.