Render strength

johniosaif

Private Member
What’s the scratch coat you’d use over cement /concrete block and then the top coat ?sand /cement
 
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loky11

Well-Known Member
Scratch coat 4-1, with waterproofer
Top coat 5-1-1 lime, cement that's what I do anyway, others may differ.
 

bobski

Well-Known Member
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?
 

bobski

Well-Known Member
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....
 

johniosaif

Private Member
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....
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
 

bobski

Well-Known Member
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

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.))
 

Rigsby

TPF Special Forces
7.5 newt blocks can be 4:1 scratch or weaker but 3.5 would be 5:1 at the strogest and thermalites I would use redagrip.
 

theclemo

Private Member
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
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.
 

johniosaif

Private Member
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.
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
 

johniosaif

Private Member
There it be
 

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FreeD

Private Member
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.
 

loky11

Well-Known Member
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.
I tend to keep scratch and top the same and never had any problems.
 
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