Internal rendering after dpc

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paradise

New Member
hi
I really need some advice from you all please..


I've been skimming and re-skimming for a while now and i am competent
but i will render an internal brick wall after dpc for the first time soon.


I want to ask a few questions..


I intend to s&c one layer 10mm then another 10mm then 2 coats of multi finish.


so


1- should I use grade m plastering sand and mix the first coat 3:1 then the second coat 4:1 ? To avoid cracks?


2- should I leave the first coat of s&c to harden overnight, scratch it then leave the second coat for 2 nights (and scratch it?) before I start to skim??


3- should I use pva or sbr on the brick work before first coat? Or in the mix? with salt inhibitor and plasticiser ?


4- can I mix the render in a bucket with drill and whisk or do I need to use a spade and board?


5- can I use my marshaltown trowel or will it damage it? should I buy a cheap trowel for it instead? what extra tools will I need than for skimming?


any other advice?!!! Pitfalls??


sorry if im asking too much!


thanks in advance
 

johniosaif

Private Member
Sbr needed if there is suction issue only., salt neutraliser if there is salts or a good chance of there been salts, I would bang on two coats of 4/1 one after the other ,flatten ,float ,leave for a week then skim, waterproofer that I use is sika1 used at ratio10/1 to water.' No plasticizer ,you can mix it anyway that suits you , I mix with cement mixer or in the bath
 

Rigsby

TPF Special Forces
You could apply an sbr slurry coat and put on a s&c coat whist the slurry is wet then scratch and let harden. The sbr will act as a tanking solution. Use sharp plastering sand and opc. Use any cement water proofer but I would go for one with a plasticizer because of the sharp sand. Leave as long as you can to second coat. 4:1 is very strong and will be waterproof but it may crack if rushed and is too thick. I would second coat with weaker mix as the waterproofing has been done already. If this is 20mm thick then 3 coats. Leave to dry out well before skimming.

I did a similar job in 86 and got called back 6 months later. 3:1 scratch, 4:1 second coat then skim. Cracked in all directions. It was on a bitumen sand blinded tanking solution though. Had to re-skim it.
 

Rigsby

TPF Special Forces
Depends what part of the Country you are in. North Yorkshire for example is it like 2mm grain but here in South yorkshire a washed sharp looks more like building sand but sharp grains of sand rather than round grains of sand like building sand has.

Dri-coat or limelite would be an answer but no good for a first timer.
 

johniosaif

Private Member
Depends what part of the Country you are in. North Yorkshire for example is it like 2mm grain but here in South yorkshire a washed sharp looks more like building sand but sharp grains of sand rather than round grains of sand like building sand has.

Dri-coat or limelite would be an answer but no good for a first timer.
Very true re sand
 

paradise

New Member
Thanks rigsby nice advice..


so I'm going to


1-sbr slurry coat


2- first coat 4/1 with salt inhibitor and silka1 waterproofer whilst sbr wet
-- scratch and leave for 2 days


3- second coat 4.5/1 without salt inhibitor or waterproofer
-- scratch and leave for 2 days


4- third coat 4.5/1 no salt inhib or waterproofer then leave to dry out for 1 week


5- pva and skim as usual


obviously don't bridge the dpc - leave 2 inch gap from ground..
i think to use the grade m plastering sand as it sounds easier to use


Rigsby I would be over the moon if u could tell me if this sounds ok


Keithuk. - it's a paid job and it is true that I have to start somewhere. I'm a self taught plasterer (bonding and skimming) and in the past 6 months put myself out there. No complaints yet.
if it f@&ks up I will stay till it's correct!


I understand I'm going to sound naive but anyway thanks for the replies everyone


:)
 

raytheplasterer

Well-Known Member
the thing about sand cement is you can't mess around with it straghening and making it look pretty or it will fall off the wall, it takes a deft hand, but no doubt you'll find that out.
 

Arti

Well-Known Member
Thanks rigsby nice advice..


so I'm going to


1-sbr slurry coat


2- first coat 4/1 with salt inhibitor and silka1 waterproofer whilst sbr wet
-- scratch and leave for 2 days


3- second coat 4.5/1 without salt inhibitor or waterproofer
-- scratch and leave for 2 days


4- third coat 4.5/1 no salt inhib or waterproofer then leave to dry out for 1 week


5- pva and skim as usual


obviously don't bridge the dpc - leave 2 inch gap from ground..
i think to use the grade m plastering sand as it sounds easier to use


Rigsby I would be over the moon if u could tell me if this sounds ok


Keithuk. - it's a paid job and it is true that I have to start somewhere. I'm a self taught plasterer (bonding and skimming) and in the past 6 months put myself out there. No complaints yet.
if it f@&ks up I will stay till it's correct!


I understand I'm going to sound naive but anyway thanks for the replies everyone


:)

Why do you need 3 coats of render?. I wouldn't wait 2 days between coats I would top the scratch the day after while the scratch is still green if I was using S&C IMO
 

raytheplasterer

Well-Known Member
hopefully you won't have these blokes chasing after you.

2043067.jpg
 

paradise

New Member
Why do you need 3 coats of render?. I wouldn't wait 2 days between coats I would top the scratch the day after while the scratch is still green if I was using S&C IMO

well it was suggested that to achieve 20mm then 3 coats will be more effective than 2
to avoid cracking.. not the case?
 

Arti

Well-Known Member
That's the re rendering spec for Kingfisher. It bonds the coats better and as long as you give it time to shrink before you skim it you'll be ok.
 
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