Different newton in bockwork

[solway]

Hi all,started a job the other day. Got set up to scratch a gable. The bottom half of the gable is built from 7newton concrete blocks and the top half is built from 5newton blocks. We wet down the gable as usual,scratched at 4-1 with plasticiser and holy fcuk the top half of the gable pulled in like crazy. the bottom half of the gable was built 9 years ago and the top half is built only 3-4weeks. we thought the bottom half would suck in like crazy but it happened the other way around. On asking the foreman where he got the blocks from he told us the supplier and said that the new blockwork is 5newton compared to the old blockwork being 7newton. Would this cause the scratch to pull in superfast because the bottom half of the gable behaved normal.

 

[plasterjfe]

7n is more dense therefore slower suction. The weaker the block normally the higher the suction. So what happened is what should have happened. You want some sbr in your scratch coat.

 

[solway]

The gable is scratched and going to finish it tomorrow. What would have been your scratch coat mix and how were we to know there was a difference in the blocks..

 

[solway]

Actually there was a mix up in the info I received from the foreman. It's the other way around. 7newton on top and 5newton on the bottom. So what happened should not have happened...

 

[plasterjfe]

No i see, well its scratched out and if a decent scratch coat there shouldnt be any issues topping it out going forward.

 

[solway]

Ya we finished it there 8/10 days ago. We wet it down a couple of times a day for 2 days in advance of finishing. It turned out fine and no rapid suction issues. Mixed at 27 sand,5 cement and 1 lime (shovel fulls) with 60ml evoplast w'proffer.