Render strength

johniosaif

johniosaif

Private Member
What’s the scratch coat you’d use over cement /concrete block and then the top coat ?sand /cement
 
Last edited:
Scratch coat 4-1, with waterproofer
Top coat 5-1-1 lime, cement that's what I do anyway, others may differ.
 
Not one mix for all.

Depends on the blocks - Totally.

Themalite/durox lightweight would be one mix, then medium density - bit stronger, heavy concrete stronger again.

What you going over?
 
Similar to the two above have said mate.

I'd go 4 to 1 on the scratch with freeflo and bang some fibres in. If below damp or if retaining wall, strengthen to a 3 to 1.

I like to mesh around any openings aswell, either fibreglass or eml to brace it up.

Top coat you can go same again or go one weaker. Few variables for top, depending on exposure, size of wall and surroundings and if they're gonna paint it etc.

But generally similar to above.

Also there's a big difference in type and quality if the sand you're getting too.
Some washed stuff I've had has had no life at all, so need to adjust and add lime etc....
 
bobski said:
Similar to the two above have said mate.

I'd go 4 to 1 on the scratch with freeflo and bang some fibres in. If below damp or if retaining wall, strengthen to a 3 to 1.

I like to mesh around any openings aswell, either fibreglass or eml to brace it up.

Top coat you can go same again or go one weaker. Few variables for top, depending on exposure, size of wall and surroundings and if they're gonna paint it etc.

But generally similar to above.

Also there's a big difference in type and quality if the sand you're getting too.
Some washed stuff I've had has had no life at all, so need to adjust and add lime etc....
Click to expand...
A guy on Irish plasterers was saying 3/1 scratch every time on concrete block , I said I’d always go 4/1 and 4/1/1 top
 
johniosaif said:
A guy on Irish plasterers was saying 3/1 scratch every time on concrete block , I said I’d always go 4/1 and 4/1/1 top
Click to expand...

On mediums, I don't think there's anything wrong with a 3 to 1 scratch, admix or waterproofer (quality of) is just as important for me.
Love fibres in there aswell. 2.2mm or even 6mm (big help) - another binder.

((3 to 1 (scratch or top) on thermalites or durox is a no go though.))
 
johniosaif said:
A guy on Irish plasterers was saying 3/1 scratch every time on concrete block , I said I’d always go 4/1 and 4/1/1 top
Click to expand...
He is worng to strong of a mix 4-1 minimum for scratch. Scud 2-1 leave for a good few weeks is a good job helps to give even suction if u scud the joints of the blocks. As the f**k**g brickies mix theres like dust.
 
theclemo said:
He is worng to strong of a mix 4-1 minimum for scratch. Scud 2-1 leave for a good few weeks is a good job helps to give even suction if u scud the joints of the blocks. As the f**k**g brickies mix theres like dust.
Click to expand...
His father taught him and he worked with plasterers with 20 years more experience than me and they use 3/1 , they must be old bastards
 
There it be
 

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You don't have to go weaker...in fact in my opinion it's best to keep the scratch and top the same strength as you would with a modern bagged render. Just make sure it's not stronger on top.

We always used to do 4-1 with full dosage of waterproofer...then top 4-1 with half dosage of waterproofer.

Been back to the jobs I did 10 years ago and still look perfect today.
 
FreeD said:
You don't have to go weaker...in fact in my opinion it's best to keep the scratch and top the same strength as you would with a modern bagged render. Just make sure it's not stronger on top.

We always used to do 4-1 with full dosage of waterproofer...then top 4-1 with half dosage of waterproofer.

Been back to the jobs I did 10 years ago and still look perfect today.
Click to expand...
I tend to keep scratch and top the same and never had any problems.
 
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