rendering

[dan007]

hi been plastering and rendering a few years lately having a problem with render blowing cracking and sometimes top coat appears weak ie easily marked when ladders leant against them i always soak walls first with water use washed plastering sand 4 and 1 cement use addmixture everbuild 3 in 1 premium waterproofer retarder & plasticiser to slow down setting time then soak the scratch coat then apply top coat with 5 sand 1 cement again with the 3 in 1 add mix as above then float wall and sponge granted last job was on relatively hot day and sun was on wall all afternoon could the 3in 1 additve in both coats be making it weak or would it be worth using lime never used it before always used plasticiser instead the finish looks great please advise
i also have to render wall that has been plyed then felted we have then fixed eml then done a slurry coat of cement mixed with sbr bond then rendered as above i know im after lot of info in one question please help

 

[Micilin]

Lot going on there.

- has it been a long time in the mix, or retempered ( mixed again)
- has it been too hot/too dry (so dried rather than set)
- are you adding a retarder and waterproofer and plasticiser ie seperate admixes?
- 3 in one, do you mean 3 parts water to one admix?

 

[dan007]

Thanx for the reply was the sand cement mix ratios ok
It was hot on the days the rendering was done and the sun did catch it all afternoon soaked the walls but was drying out quite quickly.It wasnt remixed again at all .
The 3 in 1 admix is from one bottle which includes waterproofer plasticiser and retarder (evermix 3in1) not seperate admixes .
I used it in both coats scratch & float coat mixed my gauging water in ratio 20 parts water to 1 part admix as in instructions (just used this no additional water ).
Put it down to just to hot drying out to quick rather than not setting but wasnt sure questioned myself so seeked some more advice as your never to old to learn Thanx for your help

 

[Micilin]

Mixes okay, admix okay.

No problem in both coats.

Sounds like too hot on the day (possibly overmixed or left in the mixer too long).

While lime won't solve this, personally I like lime in the top coat rather than admix as it makes it better for rubbing up and less prone to cracking.

Not clear on what you need advice on the timber wall for.

I would advise building paper or similar behind the mesh. I'd also advise at least 100mm lap at all joins.

Only advice in future is try and apply in the shade .

 

[dan007]

many thanks your a star