patience isn't a virtue............it won't go stiff!

[DIYedboy]

Why is it we only learn because we've fouled it up first!
I have just rendered a dense concrete block wall. I finished spreading today at 1pm and it didnt stiffen till 7,30pm, it was then too dark to rub it up etc.
the first coat was done sunday, 2 parts soft, 2 parts rendering sand, 1 part cement and waterproofer added and put on 15mm thick (that took 3 hours before I could tool it).
Today's coat was 3 plastering 1soft 1 cement plus waterproofer and again 15mm thick.

I need help

 

[jbonding]

sounds like too much waterproofer in your scratch coat.

 

[DIYedboy]

I used it at a 30water to 1 waterproofer ratio, is the 15mm too thick?

 

[roughcaster]

First of all, a coat of render 30mm thick overall (2 coats@ 15mm), is a huge amount to put on a dense concrete block wall, I think you know that now......12 to 15 mm thickness overall (maximum) would have been ok. (2 coats @ 6 or 7 mm)...You said "the first coat was done on Sunday, and it took 3 hours before you could tool it", ( scratch it ?) and the second coat put on yesterday (Tuesday), took 6 hours or more to tighten up. No wonder.....My reasons for thinking that:: Each coat far too thick, little or no suction, top coat probably left smooth after being put on with the trowel, rather than screeding it over with a feather/straight edge, which opens up the surface, and lets a bit of air in, and helps to tighten up the coat, maybe the mortar wasn't aerated enough,,, did you wet/overwet the wall before putting on the top coat,,was it a damp day,,,, lots of things it could be, but for me, at the top of my list it would be that both coats were far too thick. As you said, you learn as you go.

Roughcaster.

 

[DIYedboy]

Thanks for the response Roughcaster, yeah, 3 hours before I could rule up the scratch coat n 'scratch' it. I couldn't do anything with the topcoat cos if I touched it, it would crack/slump, after the 6 hour wait, it had stiffened slightly so my girlfriend came out with a torch so that I could see to screed the stuff. I didn't wet the scratchcoat before applying the topcoat (thank god!)

Sunday was HOT hence the 3 hours I suppose, Tuesday was dry but overcast............Jeez if it had been drizzling I could have gone on holiday and still come home n rubbed it up!