Render advice

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mat1234

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Hi

Need some advice regarding rendering my own house. We run a building company but get involved with little rendering.

The house is half heather bricks and half new concrete blocks. There is about 125 m2 to render. I have considered self coloured render but all the jobs around here look stained and dirty at 5 yr mark. I think a system which is paintable is best.

I am looking for a 15mm finish, very smooth and paintable. I have to get this right as the window reveals get rendered before the windows are fitted, so to do again would be a nightmare after windows are in.


I have a team of highly skilled plasterers who have some render experience but are looking to me for the spec. I got them to do a couple of test panels on a garage wall due for demolition and it looked good

4 to 1 scratch with feb

5 /1 /1 top coat with lime

All plastering sand and ordinary Portland cement ( no additives)

Sponged finished on one panel, sponged finish and then metal troweled twice on another.


They complained the top coat with lime was un workable until a water proofer 3 in 1 was added ?? thought hydrated lime was a plasterciser.


Finish wise the standard sponge was a bit sandy, would look like sandtex if painted with smooth masonary. Although a light brush when hard may solve this .The trowelled finished looked better but it had slight lows where it obviously doesn't work like multi finish. Unsure if this is achievable over 125m2 rather than 1 m2

My questions are

I want it smooth and sharp, is sponge best
Should we use a slurry coat due to bricks and concrete
Should I mesh the vertical joint of the bricks and concrete blocks, and mesh anywhere else?
Should we use stronger or weaker mixes
Should we use waterproofer in the scratch coat to prevent suction. Will the retarder be wanted at this time of year ( poss single digit tempertures)
Should we use waterproofer in the top coat, or lime or are both compatiable
Do I need frost proofer for safety, one 15m x 5m wall is north facing and doesn't get much light or even an accelerator ?
Is S/C old hat and should I be using a more modern product that can be trowel finished and painted ?

My concerns are the correct mix and the fact the render is going on at this time of year. I would be painting with keim mineral paints

Any advice welcome

Thanks

Matt
 
Maybe get someone off here who knows what they are doing, Sounds like you have a highly skilled team of skimmers but not plasterers otherwise you wouldn't be asking these questions. You need a waterproofed In Your scratch for starts, have a read around the forum there is plenty of advise on rendering oh and welcome xx
 
bobby said:
Ask Cassie.he's the guy who will know all the answers.he was taught @ college.lol


I'm using The Plasterers Forum Mobile App
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no need to be jealous .. you can always get on an adult learners course... that way you would be able to answer questions with the correct way of doing things.. if people such as your unqualified self dont want to listen.. hey. I dont give a fuk..lol
 
cassie said:
no need to be jealous .. you can always get on an adult learners course... that way you would be able to answer questions with the correct way of doing things.. if people such as your unqualified self dont want to listen.. hey. I dont give a fuk..lol
Click to expand...

LOL. just realised Bobby.. your the guy who doesn;t know about thicknesses.. got ya.. you would only need a short course mate, they teach the basics early on..lmao...
 
cassie said:
LOL. just realised Bobby.. your the guy who doesn;t know about thicknesses.. got ya.. you would only need a short course mate, they teach the basics early on..lmao...
Click to expand...

Ouch!!!!


I'm using The Plasterers Forum Mobile App
 
Windows in first! Plastering sand and cement with a waterproofer like the 3 in 1 mentioned. Strength? Well for flat render i think 4:1 is too strong you might get cracks or crazing more 5:1. Top coat slighter weaker (and thinner lol) with or without lime but a plasticiser is a must. Sand, cement and lime only will be dead as a do-do and will slump giving slump cracks. At this time of year though it is the setting time what will be a problem, you could use one of those accelerators with plasticiser added but take advice regarding lime with accelerators. Some react with lime.

Better still get a proper renderer in with a machine and spray it on with Weber ocr or the like. 15mm in 2 passes same day.
 
Batten it board it then tape joint it, have a look if a system exists
the finish you're after doesn't exist float or trowel finish it's never perfect
 
,scratch it,3-1 with waterproofer and feb,top coat 5-1-1 or half bucket of lime,and feb,Darby and float up with plastic float.
use a gritty sand,something like washed grit sand(washed waddy fell up my way)
gives a good finish.
and what the **** is a trowel finish on render? Is this a real finish,never heard of it.
and if you 'top notch plasterers can't render,they ain't plasterers ;)
 
mat ,if i where you i would get a quote from a proper plasterer one who can render. this is a trade, not something that you pickup like the clap.
 
Rigsby said:
Windows in first! Plastering sand and cement with a waterproofer like the 3 in 1 mentioned. Strength? Well for flat render i think 4:1 is too strong you might get cracks or crazing more 5:1. Top coat slighter weaker (and thinner lol) with or without lime but a plasticiser is a must. Sand, cement and lime only will be dead as a do-do and will slump giving slump cracks. At this time of year though it is the setting time what will be a problem, you could use one of those accelerators with plasticiser added but take advice regarding lime with accelerators. Some react with lime.

Better still get a proper renderer in with a machine and spray it on with Weber ocr or the like. 15mm in 2 passes same day.
Click to expand...
Most frost proofers state that you musnt add other admixes to them Rigs
 
Aye so its a problem because u need waterproofer i couldn't find any way around it for sand cement at the start of the year as they all seem to say no other additive
 
Thanks for your views guys. the problem seems to be so many people have diferant views over the method.. I could get an alternative team in but whos to say they know best ? I have no doubt my guys can get it on fair and true to a good finish, I just lack the chemistry knowledge regarding additives, and the ways of bending it to suit this time of year. I still see people preaching on here that stronger and thicker coats than before work, although an hour of research shows that's pretty high risk.

My outstanding questions are, is a waterproofer needed in the scratch coat at this time of year, or just a plasteriser. Theory being the top coat will not be drying that quickly and suction not so much off a problem, also does it need retarding ?

Is the waterproofer only used to control suction of the next coat. If the wall is to be painted then a waterproofer is / not needed in the final topcoat ?

So it is ok to use a plasteriser with lime

After all these years of s/c has no body written a british standards guide to rendering, with a what you can and cant do.
 
My guys are very skilled and quite happy to just get on with it. But like on here they have their preferred method and additives. The thing is if it fails in 5 yrs time when there long gone then I will foot the bill. havin worked this industry for 20 plus yrs Ive learned to trust no one and question all. I respect their ability but not chemistry. I am therefore researching the best practises to minimise risk of future failure
Matt
 
lucius said:
Most frost proofers state that you musnt add other admixes to them Rigs
Click to expand...

Thanks for the advice. The render must be done first as it how the window system works. The modern way of fitting them is to use a expanding tape from render to frame, apprx 15mm. They are the same as been used in the last three episodes of grand designs, VELFAC
 
The waterproofer is used to control the suction on the top coat but also to waterproof the building, you start with a stronger mix then get weaker or it will crack or fall off.
 
mat1234 said:
Thanks for your views guys. the problem seems to be so many people have diferant views over the method.. I could get an alternative team in but whos to say they know best ? I have no doubt my guys can get it on fair and true to a good finish, I just lack the chemistry knowledge regarding additives, and the ways of bending it to suit this time of year. I still see people preaching on here that stronger and thicker coats than before work, although an hour of research shows that's pretty high risk.

My outstanding questions are, is a waterproofer needed in the scratch coat at this time of year, or just a plasteriser. Theory being the top coat will not be drying that quickly and suction not so much off a problem, also does it need retarding ?

Is the waterproofer only used to control suction of the next coat. If the wall is to be painted then a waterproofer is / not needed in the final topcoat ?

So it is ok to use a plasteriser with lime

After all these years of s/c has no body written a british standards guide to rendering, with a what you can and cant do.
Click to expand...


Surely the simple answer is a pre bagged ocr then
 
mat1234 said:
My guys are very skilled and quite happy to just get on with it. But like on here they have their preferred method and additives. The thing is if it fails in 5 yrs time when there long gone then I will foot the bill. havin worked this industry for 20 plus yrs Ive learned to trust no one and question all. I respect their ability but not chemistry. I am therefore researching the best practises to minimise risk of future failure
Matt
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i have little faith in your plastering team producing a quality job.
when you tell me that they brought sand to the surface, then they finished the panel with a trowel. having no idea on the mix or application. then you have no chance of a decent finish.
 
malc said:
i have little faith in your plastering team producing a quality job.
when you tell me that they brought sand to the surface, then they finished the panel with a trowel. having no idea on the mix or application. then you have no chance of a decent finish.
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What is this finishing wall with a trowel ? Troweling up s/c like skim,really,can it be done Malc :)
 
craigw said:
What is this finishing wall with a trowel ? Troweling up s/c like skim,really,can it be done Malc :)
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We did it in cow sheds and stables,I can only assume it's for hygienic purposes,so the walls can be hosed down and reduce built up of muck and bacteria


I'm using The Plasterers Forum Mobile App
 
craigw said:
What is this finishing wall with a trowel ? Troweling up s/c like skim,really,can it be done Malc :)
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the op had some test panels made to see the quality of a sand and cement rendered finish for his new house. one panel they had sand on the surface an other they flatterned it with a trowel.
 
I would go for the through colour seeing as though you like the look of it, it just needs sealing to keep it looking brand new.
 
mat1234 said:
Thanks for your views guys. the problem seems to be so many people have diferant views over the method.. I could get an alternative team in but whos to say they know best ? I have no doubt my guys can get it on fair and true to a good finish, I just lack the chemistry knowledge regarding additives, and the ways of bending it to suit this time of year. I still see people preaching on here that stronger and thicker coats than before work, although an hour of research shows that's pretty high risk.

My outstanding questions are, is a waterproofer needed in the scratch coat at this time of year, or just a plasteriser. Theory being the top coat will not be drying that quickly and suction not so much off a problem, also does it need retarding ?

Is the waterproofer only used to control suction of the next coat. If the wall is to be painted then a waterproofer is / not needed in the final topcoat ?

So it is ok to use a plasteriser with lime

After all these years of s/c has no body written a british standards guide to rendering, with a what you can and cant do.
Click to expand...
not being funny but you're on the internet asking people you don't know what to do ? You're plasterers are you're best bet mate go to them for advice, if they don't know what there doing get someone who does
 
I am hopefully asking people who are at the top of their game, advice on the effects of playing with different mixes and additives. Hence why I am on this forum.

I have spoken to weber today who where very helpful. Picked up 3 bags of OCR to play with tomorrow. Also got a drop of k-rend accelerator to see if this would be a benefit ( advised by the supplier and three other renderers at the trade counter it kicks it off nicely in the cold, but who knows as there are 100 different opions out their !!) Spoken to weber about using frost proofer. They reckon it should be ok as nothing in it should affect ocr, but they have never tested it ! Bout time they did . Will search this forum for other tips reguarding ocr
 
mat1234 said:
I am hopefully asking people who are at the top of their game, advice on the effects of playing with different mixes and additives. Hence why I am on this forum.

I have spoken to weber today who where very helpful. Picked up 3 bags of OCR to play with tomorrow. Also got a drop of k-rend accelerator to see if this would be a benefit ( advised by the supplier and three other renderers at the trade counter it kicks it off nicely in the cold, but who knows as there are 100 different opions out their !!) Spoken to weber about using frost proofer. They reckon it should be ok as nothing in it should affect ocr, but they have never tested it ! Bout time they did . Will search this forum for other tips reguarding ocr
Click to expand...
The thing is Mat, you say that the guys on here have a difference in opinions, but their way of thinking and opinions have come from years of experience pushing the stuff up the wall! They know their way works, theres more than one way to skin a cat remember.
If your lads had anything about them, the last thing they would be doing is looking to you for advice on ratios and additives. I would recommend you look to get someone experienced in rendering, thats happy to show you examples of there work in the past. Good luck.
 
lucius said:
Most frost proofers state that you musnt add other admixes to them Rigs
Click to expand...

I meant the frost proofers that have a plasticiser already in them like Wintabuild etc. Everbuild do one but cannot remember the name of it. MKM sells it.
 
Went out and picked up 3 bags of ocr and a tub of k-rend accelerator today. had the test panel up by 10am , rubed it up about 3 hrs later and finished with a sponge. This stuff is fantastic. the guys loved it and the fine finish is top knotch. 16mm in one hit , no sags, water bleed or any problems. It definatley needed the accelerator as it was only 5 degrees but it was hardish by 5pm . ordered another 170 bags, and scraped the sand and cement route. I think material wise it will be about 40 % more than s/c but their will be a big saving in labour. Thanks to those who suggested OCR
 
This k rend accelerator? Is it their mono accelerator? If so the Weber mono accelerator would do the same?
 
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