re rendering

[pwi]

hi guys ive a huge gable end to re do it was done very poorly before so ive knocked of the top coat and want to re do in smooth render what would you recomend mix wise i dont want it going of to fast ???

 

[spunky]

if youve still got the key from the scratch coat i'd give it a good soaking or you could grind a 5-1 scratch coat with waterproofer before you top it, if the keys lost i'd rendaid it and start again

 

[pwi]

still got a good key what would you think mix ratio should be

 

[spunky]

at least 5-1-1 try and lay a bit on have a cup of tea and see what it pulls in like

 

[pwi]

do you prefere waterproofer or the sbr in your mix

 

[spunky]

neither for the top mix mate just a good couple of shovels of lime

 

[pwi]

i do like lime but done a job a while back top coat was 5-1-1 and it was great until next day it had small hairline cracks in it im sure it was lime that caused it

 

[spunky]

it shouldnt be mate limes a bit of the norm ...............so are hairline cracks

 

[pwi]

ill be honest i think the one big problem we have in scotland is we cant get good plastering sand we render with building/soft sand no good really ,nice to hear that its not just me who experiences cracks though

 

[spunky]

ive only ever used a local sand mate some of the other lads might be able to help you out

 

[rockhardsolidplastering]

i think two big reasons for render top coat cracking are going over scratch coat too soon not cured and not floating properley just my oppinion tho

 

[essexandy]

ill be honest i think the one big problem we have in scotland is we cant get good plastering sand we render with building/soft sand no good really ,nice to hear that its not just me who experiences cracks though

I would guess you're spot on, sand for rendering needs to be clean (no silt content), can't see lime causing the cracks. I totally agree with what rocksolid said. Also if rendering over someone else's base coat you need to access the strength of their mix and make sure that your mix is weaker, unless their mix is to weak to do so without having to make your mix to weak for an external finish, in which case their base coat needs removing and starting afresh.