Blown is render

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johniosaif

Private Member
Did a house in sand and cement render ,went fine no problems, then the neighbour asked me to render hers, front ,hack of re,render,went fine,did the bottom at the back same dime,did the first floor it at the back,it has hundreds of small cracks when wet, some parts seem to be weak,we have hacked of two walls ,the other is very solid but has lots of minor cracks,solutions I seek,primed it with sbr 2/1 ,intend to render it again with 5/1 sand and cement ,maybe a sbr scud first.. This has ever happened to me before and it feels horrible buti want it done,it's at my expense obviously.
 

irish_spread

Private Member
Where did you get your sand ? Maybe a high clay content, closer to soft sand maybe ?
What type of bricks ?, I know a lot of people like weaker mixes but I prefer 7:2:0.5 especially on re renders. Lime seems to make the mix pick up quicker, maybe rapid set ?

Dont know the answer myself like, just suggestions
 

johniosaif

Private Member
Where did you get your sand ? Maybe a high clay content, closer to soft sand maybe ?
What type of bricks ?, I know a lot of people like weaker mixes but I prefer 7:2:0.5 especially on re renders. Lime seems to make the mix pick up quicker, maybe rapid set ?

Dont know the answer myself like, just suggestions
A few odd things, it was hot,the scratch was very dry,even when hosed, the sand was different her,came from jewsons and was more sharp than fine sharp,we had it6/1/1 and there was a cheap waterproofer in it also
 

bobspread

Well-Known Member
Did a house in sand and cement render ,went fine no problems, then the neighbour asked me to render hers, front ,hack of re,render,went fine,did the bottom at the back same dime,did the first floor it at the back,it has hundreds of small cracks when wet, some parts seem to be weak,we have hacked of two walls ,the other is very solid but has lots of minor cracks,solutions I seek,primed it with sbr 2/1 ,intend to render it again with 5/1 sand and cement ,maybe a sbr scud first.. This has ever happened to me before and it feels horrible buti want it done,it's at my expense obviously.
Cant help you out on this one Johnio but what a guy coming on here holding your hands up , 48years of age and **** still happens mate, unlike some younger ones on here who have never had a callback
 

irish_spread

Private Member
All sounds ok :confused:. Thin rubbing up coat ? Seen an ethnic down the road from doing what seemed a reasonable job but months later the owner, also an ethnic knocked at my door saying it started cracking then started shelling off. Had a look at it and
1. A fine sand
2. Bad scratch key
3. Top coat far to thin

maybe ?
can send u pics if you want

Ethnic said I no want expensive repair, only vanting cheap on top coat for value.
I gave him The Samaritans number
 

tam

Active Member
I like my mix stronger than that to be honest, I like to keep it 3 sand 1 cement scratch and 4 sand 1 cement 0.5 lime float. Lime is optional.
 

johniosaif

Private Member
I like my mix stronger than that to be honest, I like to keep it 3 sand 1 cement scratch and 4 sand 1 cement 0.5 lime float. Lime is optional.
Problem with that is in England we are rendering period properties, 100 plus years old built with bricks and mortar,the are moving continuously ,due to thermal mass ie and the elements, the mix you use wouldn't work on these properties.in my opinion
 

johniosaif

Private Member
All sounds ok :confused:. Thin rubbing up coat ? Seen an ethnic down the road from doing what seemed a reasonable job but months later the owner, also an ethnic knocked at my door saying it started cracking then started shelling off. Had a look at it and
1. A fine sand
2. Bad scratch key
3. Top coat far to thin

maybe ?
can send u pics if you want

Ethnic said I no want expensive repair, only vanting cheap on top coat for value.
I gave him The Samaritans number
Floating coat was min 12 mm mostly 15 mm
 

xyzplasterer

New Member
A few odd things, it was hot,the scratch was very dry,even when hosed, the sand was different her,came from jewsons and was more sharp than fine sharp,we had it6/1/1 and there was a cheap waterproofer in it also

Maybe no waterproofer in scratch? Check the sand out...maybe too many impurities...high clay content?.....

I'd hack off, Rendaid then OCR.
 

johniosaif

Private Member
Maybe no waterproofer in scratch? Check the sand out...maybe too many impurities...high clay content?.....

I'd hack off, Rendaid then OCR.
Had waterproof in scratch, left it four days before float,it was during very hot weather and on a felt roof with lots of glass,
 

tam

Active Member
Problem with that is in England we are rendering period properties, 100 plus years old built with bricks and mortar,the are moving continuously ,due to thermal mass ie and the elements, the mix you use wouldn't work on these properties.in my opinion

Yea maybe a small bit weaker will do no harm but I don't like my scratch being too weak. All the bag renders seem very strong.
 

xyzplasterer

New Member
Too many variables mate, take it back to brick, use bagged render, protect it form the weather and mist it down and I doubt you will have a problem.

We have had 'tension cracks' with OCR since they changed to ECO....
 

malc

TPF Special Forces
there is always one side of a house that takes all the weather it bakes in the sun and takes the rain in bad weather, causing problems for sand and cement render.
the waterproof additive that we use states add extra cement to the mix.
we render in sharp sand adding a little plastering sand to top coat if required. the sand that i have seen at jewsons for plastering is far to soft.
are they london stock bricks with pointed joints ?
 

johniosaif

Private Member
there is always one side of a house that takes all the weather it bakes in the sun and takes the rain in bad weather, causing problems for sand and cement render.
the waterproof additive that we use states add extra cement to the mix.
we render in sharp sand adding a little plastering sand to top coat if required. the sand that i have seen at jewsons for plastering is far to soft.
are they london stock bricks with pointed joints ?
Yes,London stocks,but no pointing ,it was rendered originally
 

zombie

Private Member
sorry to hear your dramas john and as bobby said hands up for being man enough to ask for suggestions...this is what scares the arse out of me with render done bits and bobs with sand and cement and it always seems like seat of your pants time until completed unless its just the guy I do bits with as in blind leadind the blind...

im also in the mind set that these modern pre bagged and mesh systems have got to be theway1 to go for me takes the guess work and potential floors of the mix out of the equasion I recon...

just leaves you to concentrate on the application then I think...

Done a few thin coat systems lately with silicone top coats and cant praise these systems enough in comparison for user friendliness of gear and the science behind the whole system...

but as said I no very little about rendering in general so maybe im well of the mark I dunno but for the minute any rendering that comes my way at mo it gets a price for a thincoat only or newt

good luck pal:RpS_thumbup:
 

church

Well-Known Member
there is always one side of a house that takes all the weather it bakes in the sun and takes the rain in bad weather, causing problems for sand and cement render.
the waterproof additive that we use states add extra cement to the mix.
we render in sharp sand adding a little plastering sand to top coat if required. the sand that i have seen at jewsons for plastering is far to soft.
are they london stock bricks with pointed joints ?


this is all bullshit , you either know what your doing or you dont , its got very little to do with sand types , thats just forum talk
 

flynnyman

Well-Known Member
Did you wet the scratch before you topped it? Did the same lab mix for both houses? Probably the sun getting it too quick should of worked with the sun but that won't be a problem soon :(
 

bobspread

Well-Known Member
Can you still get the famous Leighton Buzzard sand down there?it never used to slump like the gear up north.
 
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