Rendering new blockwork extension

[ffg]

Hi

I'm (self)-building a garage /workshop and living room extension, and the next stage is rendering the outside blockwork of the garage. It's built of dense 7N concrete blocks, 100mm, cavity wall.

I'm fairly confident at internal plastering with gypsum plasters, but never rendered a big area outside before. I have an electric mixer.

Looking for advice:

Wall preparation - do I need a dilute PVA coat?

Wet the wall before applying scratch coat?

Render mix - I'm thinking scratch coat 4:1 sand:cement with render plasticizer - yes? What kind of sand? About 5-7mm (walls are pretty straight!)

How wet to mix the s&c?

Scratch the base coat but not right through to blockwork.

Next day

Top coat 1:1:7 cement:lime:sand - what sand? About 3mm?

Finish with sponge or float?

Thanks

 

[Micilin]

Hi

I'm (self)-building a garage /workshop and living room extension, and the next stage is rendering the outside blockwork of the garage. It's built of dense 7N concrete blocks, 100mm, cavity wall.

I'm fairly confident at internal plastering with gypsum plasters, but never rendered a big area outside before. I have an electric mixer.

Looking for advice:

Wall preparation - do I need a dilute PVA coat? NO

Wet the wall before applying scratch coat? NOT WITH THOSE BLOCKS BUT WET A SMALL AREA A FEW DAYS BEFORE < SEE HOW IT SUCKS IN

Render mix - I'm thinking scratch coat 4:1 sand:cement with render plasticizer - yes? What kind of sand? About 5-7mm (walls are pretty straight!) 4:1 Fine sharp sand (rendering sand 3mm down, washed salt free) with plas is fine . Coat thickness depends on what you need to straighten out the wall

How wet to mix the s&c? You'll have to guage this yourself, it's got to have a bit of life in it, so that it is spreadable, but not over-mixed or you will ruin it. It wnats to sit up a bit on the hawk, maybe someone elsecan explain better

Scratch the base coat but not right through to blockwork. Yep. Make sure scratch coat flat enough to give you even top coat thickness. Do all the filling out etc in the scratch coat

Next day

Top coat 1:1:7 cement:lime:sand - what sand? About 3mm? Same sand as above, I would go 1:1:5. Should not need plas with this.

Finish with sponge or float? Rule off , float and then light sponge when it picks up a bit, but before it goes too hard. Again, hard to describe

Thanks YOur welcome, come back with any more

 

[Monkeh]

I just have to ask, do you realise how ridiculously difficult it is to read that? Please use quotes properly.

 

[roughcaster]

do you realise how ridiculously difficult it is to read that?

You should have gone to Specsaver's then Monkeh!!!

 

[external]

I just have to ask, do you realise how ridiculously difficult it is to read that? Please use quotes properly.

good advice tho m8,did you have anything to add ?

 

[Monkeh]

do you realise how ridiculously difficult it is to read that?

You should have gone to Specsaver's then Monkeh!!!

Actually I did. Doesn't help when you have to read two posts at once to figure out what's been added inside what is meant to be a verbatim quote.

good advice tho m8,did you have anything to add ?

I'm no plasterer, so no.

 

[Micilin]

do you realise how ridiculously difficult it is to read that?

You should have gone to Specsaver's then Monkeh!!!

Actually I did. Doesn't help when you have to read two posts at once to figure out what's been added inside what is meant to be a verbatim quote.

good advice tho m8,did you have anything to add ?

I'm no plasterer, so no.

Sorry monkeh, I' ve spent 25 years plastering, not in IT. . I thought the lead in with capitals might give the reader a clue.

 

[trowelmonkey1]

 

[Monkeh]

Sorry monkeh, I' ve spent 25 years plastering, not in IT. . I thought the lead in with capitals might give the reader a clue.

Oh, I knew what you were doing, it's just seperating the original post from your comments is annoying.

 

[external]

can you please stop talkin english im from the black country an i just dont get it

 

[Micilin]

Sorry monkeh, I' ve spent 25 years plastering, not in IT. . I thought the lead in with capitals might give the reader a clue.

Oh, I knew what you were doing, it's just seperating the original post from your comments is annoying.

Dear Mr Pot,

Well, if we were to find syntax , grammar and poor spelling annoying there would be a lot of irate people here, and not much information exchanged.

I got the gist of what you were saying, even though your sentence is poorly constructed and contains a spelling error. But it doesn't annoy me, it's more amusing than anything else.

I'm off on my holidays, sorry for ruining your evening,

yours

Mr Kettle

 

[roughcaster]

One important thing to be aware of though FFG,,, don't let each coat dry out too quickly, especially if you scratch/render on a hot sunny day, (if we get any), but sun or wind can dry out a coat within a short period of time, making it weak and powdery. If you can, keep the render "green", and let it dry/cure slowly,, over a day or two.

 

[roughcaster]

Enjoy your holiday Micilin, you deserve it, and take care mate. See you when you get back.

 

[ffg]

Thanks Micilin, I appreciate the help (even if it was a little difficult to read... nothing wrong with yer speling tho m8...

I take it the 3mm down sand you recommend is a bit coarser than the 'building' sand I've been using for brick/blocklaying? ( I still have about 1/2 ton left) I heard some plasterers mix building sand with sharp sand for rendering?

The blocks do get saturated with water when it rains (like today!!), but they don't seem to suck like the insulation blocks I'm using for the extension interior. Would it be sensible to wet the wall if it's warm/sunny on the day? Or just wait for a cooler day?

I understood that the top coat should be a weaker mix than the scratch coat - with a 4:1 scratch, is 1:1:5 (lime:cement:sand) weak enough for the top?

Roughcaster, thanks for the tip, do I keep the render green by spraying with water?

cheers

 

[roughcaster]

do I keep the render green by spraying with water?

Yes,,,,, but """very carefully""", and the water sprayed on would be a "very very fine mist", just enough to keep the render green. On a smaller area/s, you can cover them over with polythene,, (again,, very carefully), but not on bigger areas. Sometimes, it pays you to actualy render the wall/s when the sun has moved round from that position.