SBR for render

[GlenT]

I have put a scratch coat on my shed (after much grief).Scratch coat has gone off rock hard, unlike before with measured waterproofer in it when it was powdery and had to be taken off.I used just sand cement and lime.The problem i have now is that the top coat will suck in too quick.Was wondering if i could paint SBR onto the scratch coat to help with suction? Has anyone done this?It only states on the tub about mixing it with cement to form a slurry. If so too what ratio SBR to water and do you apply render while SBR is tacky,as you would PVA or not? any advice appreciated

 

[joe-90]

Hosing it down is the easiest way.

 

[roughcaster]

Glen,,,, people use correctly measured amounts of waterproofer in scratch coats all the time with no adverse problems. You say you had to take off the previous s/coat because it was powdery, and you're blaming the waterproofer. Because of this, you have scratched the wall again "without" using waterproofer, but you now have a problem with high suction.
A proper measured amount of w/proofer would not cause mortar to go powdery. "Too much" w/p in the mix would, as would drying out too quick, or too much sand in the mix. You now have a problem to solve with the suction. As Joe suggests, giving the wall a really good hosing down 2 or 3 times will help. I've not tried the SBR method,, but to blame the failure of the scratch-coat on your interpretation of a measured amount of waterproofer i find hard to believe. Did you use a cement mixer or did you hand batch. Was the sand and cement correctly guaged? How did you measure the w/p and what brand? Was the weather warm/hot, windy when you scratched? Was the brick/blockwork dry and absorbent, or did you wet/damp down the wall first? Sorry for all the questions, but I think there's more to the failure of the scratch coat than the w/p.

 

[GlenT]

I wet the celcon blocks.The weather was cool and cloudy,not too windy.I used a measuring jug for the waterproofer.Mix was 5&1. Do you physically check your scratch coat afterwards ie by trying to scratch it off with your fingers? Once i removed this coat i soaked the wall and then applied a 5:1:1 mix,the other being lime.No man made additives with the same sand and cement as before.This has gone off rock hard you cant even scratch it with a nail(galvanised not finger).Celcon do actually state to do it this way.I have been told by a BS that within 5 years airated blocks will be no more because of the problems.

 

[iaith]

Hi Glen. sbr slurry mix will kill any suction, no need to add water , just mix it with cement, paint it on ,and let it dry. I would have painted it on to the block work before the scratch coat. those celcon blocks are very thirsty.

 

[joe-90]

Hi Glen. sbr slurry mix will kill any suction, no need to add water , just mix it with cement, paint it on ,and let it dry. I would have painted it on to the block work before the scratch coat. those celcon blocks are very thirsty.

We wet it for a reason.