Where did I go wrong?

jackarse

New Member
Hi all, I have been a member of this site for a number of years and have greatly benefitted from the advice and information gained, many thanks. I have successfully tackled internal plastering finishing whole rooms from top to bottom on bare blockwork and plasterboard.
However, I have come unstuck on my first attempt at the external rendering of a blockwork boundary wall (7n2). The first coat stuck well 4 to 1 TP plastering sand/Mastercrete cement plus 3in1 additive, applied approx 5-8mm scratched up and keep moist for a week.
The second coat 5-1 plus 3in 1 additive was applied to a slightly damped up surface at about 8-10mm, ruled off level with a feather edge left to partially set floated then sponge to finish. Again kept damp for 3 days. After about 5 days hairline cracks appeared and the render started to blow, the first coat still seems solid.

Where did I go wrong?, was the 2nd coat too thick? I know I added too much 3 in 1 additive to the first coat, I didn't use any lime or fibers ( locally not available).

Any help is greatly appreciated, I know I will have to completely strip the second coat and maybe do an SBR job?.


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jackarse

New Member
Ok thanks, Danny, so the key is ok? but the depth is far too thin?
I have now stripped off all the topcoat and re-scratched the scratch coat, my idea now is to SBR prime the scratch coat let it dry then apply an SBR cement slurry then whilst still tacky apply the topcoat to a max of 7mm to achieve a 12mm total depth finish, OR should I scratch up again and go to a third coat to achieve 19mm?.
 

Ritch

Well-Known Member
Hi all, I have been a member of this site for a number of years and have greatly benefitted from the advice and information gained, many thanks. I have successfully tackled internal plastering finishing whole rooms from top to bottom on bare blockwork and plasterboard.
However, I have come unstuck on my first attempt at the external rendering of a blockwork boundary wall (7n2). The first coat stuck well 4 to 1 TP plastering sand/Mastercrete cement plus 3in1 additive, applied approx 5-8mm scratched up and keep moist for a week.
The second coat 5-1 plus 3in 1 additive was applied to a slightly damped up surface at about 8-10mm, ruled off level with a feather edge left to partially set floated then sponge to finish. Again kept damp for 3 days. After about 5 days hairline cracks appeared and the render started to blow, the first coat still seems solid.

Where did I go wrong?, was the 2nd coat too thick? I know I added too much 3 in 1 additive to the first coat, I didn't use any lime or fibers ( locally not available).

Any help is greatly appreciated, I know I will have to completely strip the second coat and maybe do an SBR job?.


View attachment 69748 View attachment 69749 View attachment 69751
Clearly you’ve not put it on thick enough, looooooooooooool
 
Ok thanks, Danny, so the key is ok? but the depth is far too thin?
I have now stripped off all the topcoat and re-scratched the scratch coat, my idea now is to SBR prime the scratch coat let it dry then apply an SBR cement slurry then whilst still tacky apply the topcoat to a max of 7mm to achieve a 12mm total depth finish, OR should I scratch up again and go to a third coat to achieve 19mm?.
they is not good... have a look on some threads on here... I think @essexandy did a good post on rendering many years
 

Tramp

Well-Known Member
Well, hopefully, there is someone out there who can offer some constructive advice, ie best way forward.
It's all been said above your topping off is too thick and probably worked too much scratch should be horizontal
 

jackarse

New Member
It's all been said above your topping off is too thick and probably worked too much scratch should be horizontal
But the topping coat was within EssexAndys procedure ie 8 to 12mm. Scratch is mostly wavy horizontal.
But i have to say it might have been worked too much!
 

Brimstone

Well-Known Member
OK, I'm a chancer right? So t'others can shout me down but they're being a bit shy;
Your first coat is wank because it did not take out the obvious lack of vertical and/or dips/highpoints in the blockwork. That is the primary purpose of the first coat,- and even that might have to be done in 2 lots by dubbing out any really bad bits first.
Your second coat is way too thick, master spoldgers like Andy might be able to get away with it but for us mortal chancers, no chance.
Also, your scratching is wrong and maybe too shallow, and you almost certainly put it on to a too-dry surface.
I'll guess that you also tried to put it on in one pass? I find it best to do it in two thin passes, like you would for hardwall.
And if you really want it that thick, it would be a third coat, fairly skinny.
And without re-reading Andys fine work - what is this 3in1 you mention using so much? And why?
 

jackarse

New Member
OK, I'm a chancer right? So t'others can shout me down but they're being a bit shy;
Your first coat is wank because it did not take out the obvious lack of vertical and/or dips/highpoints in the blockwork. That is the primary purpose of the first coat,- and even that might have to be done in 2 lots by dubbing out any really bad bits first.
Your second coat is way too thick, master spoldgers like Andy might be able to get away with it but for us mortal chancers, no chance.
Also, your scratching is wrong and maybe too shallow, and you almost certainly put it on to a too-dry surface.
I'll guess that you also tried to put it on in one pass? I find it best to do it in two thin passes, like you would for hardwall.
And if you really want it that thick, it would be a third coat, fairly skinny.
And without re-reading Andys fine work - what is this 3in1 you mention using so much? And why?
Thanks, Brimstone a sensible post, Andy said "I always use a three in one admixture for my scratch coat (plasticiser, waterproofer and retarder)"

https://www.everbuild.co.uk/product...xtures-building-chemicals/204-evermix-3-in-1/
 

michaelckeyes

New Member
I
The scratch coat isn't keyed enough,and u expect too soft...the fi is coat is way too thick,and I suspect stronger than the scratch....too many additives in the scratch?..
IF you have too many additives in the mix,it gets (dusty)...kills the cement..I'm 40 plus years at this game brother ...ease off the additives
 

Brimstone

Well-Known Member
No scratch coat was 4-1, the top coat was 5-1.
But he's saying if too much addys then the scratch coat 4:1 could go down to 5;1 or 6;1,
and as I understand it, the thickness of each coat needs to be less than thre one before as it also increases the strength/shrinkage/summat.
 
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