Hi guys, I sprayed a 30m panel over an existing s+c scratch, floated it up lovely, only to find it had cracked all over! The rep said I should have never gone over s+c! He also said if I'd rendaid the scratch, he wouldn't guarantee that either! Although I do know someone who has rendagriped an old scratch and gone over it with no problems! Instead of using the customers house as an experiment, & losing more material, I'm considering doing the top coat in s+c! But I'm hoping someone on the forum may have encountered this before & has a solution!? Cheers Rhys.
OCR cracking help advice needed
- Thread starter dai dog
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User________removed
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Dai dog did you rub it up to soon ? how wet was it when you rubbed it up ? Does it sound hollow round the area where it cracked ?
Looks like shrinkage cracks caused by too much suction to me, could be wrong though. S+C substrates are prone to high suction rates if not prepared first. I don't think any manufacturer would guarantee a way forward from here I'm sorry to say as the render blowing is a distinct possibility.
I'd say 10mm (a little deeper in parts) it was sunny but the panel was completely covered & not windy!
johniosaif
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What was the scratch done with, what strength ,how long left before ocr went on, what additives in the scratch
Hi, the scratch was done with 4 to 1 with 2 caps of freeflo (gauged in a bucket) but the rep told me that the OCR is about a 6/1/1 which is weaker anyway!?
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Rigsby
TPF Special Forces
You may have gone over the 4:1 to early. 4:1 is strong and will need to cure well before top coating. Also this on a waterproofed base coat so shrinkage or slump cracks?
I have had had ocr crack but usually down to to thick and wet.
Not surprised the rep said what he said. Typical of Weber!
I have had had ocr crack but usually down to to thick and wet.
Not surprised the rep said what he said. Typical of Weber!
User________removed
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Not with OCR mate, only onto new blockwork.
User___removed
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In my experience with bagged render it will crack if to thick,like any render I suppose.
CPI cracks a lot as there is no suction due to waterproof.
I have done back to hand apply now with standard s&c.its cheaper for gear and easier to source.
CPI cracks a lot as there is no suction due to waterproof.
I have done back to hand apply now with standard s&c.its cheaper for gear and easier to source.
xyzplasterer
New Member
Yes I've just done one over sand cement, rendaid then ocr, no cracks. And I regularly go over sand cement 4:1 with waterproofer at 10mm without problems.
It's weird because I had the same cracks on a job recently that I sprayed did everything same as usual. I spoke to Weber and they said they were tension cracks and just on the surface? It was not hollow around the cracks so I sponged them in.
xyzplasterer
New Member
The one I've just down was hand applied, mixed up with Belle. No cracks.
Cheers pal, that gives me a bit more confidence, do you try & leave the gear as late as you can like some guys have suggested?
johniosaif
Private Member
Is rend aid over a scratch before ocr a bit ott,wouldn't a mix of 6/1/1 be easier to apply anyway... As in ordinary sand cement lime
xyzplasterer
New Member
You don't want it to be moving but thats standard. I leave it quite late, quick float then get the sponge on it. I had it once where the labourer soaked the scratch and that was a nightmare, started sliding. Just dampen it down slightly so there is still a good bit of suction.
As others have said you can't put it on too thick. I don't know what these cracks are mate it's always hard to put your finger on it I always use Rendaid but still have this problem sometimes.
If you are Tyroleaning or painting I don't think these cracks will be a problem as according to weber they are just the surface.
It is annoying though.
xyzplasterer
New Member
Thats Webers spec, yes I think it's OTT. I always go straight over the sand/cement.
johniosaif
Private Member
What advantage do you find with ocr,
xyzplasterer
New Member
To be honest it's peace of mind. It takes one major worry out of the equation and that's whether the labourer has used the right proportions etc
xyzplasterer
New Member
At least I know if it's cracked it must be something I've done wrong with the prep or weather conditions.
johniosaif
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Oh yes, we know this one,sometimes they forget the cement,
User___removed
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What scratcher do you use? I found some are better than others for key
A run of the mill 5 prong one with a plastic handle!?
User___removed
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I used to use a faithful one with plastic handle then changed to a different one as it was sagging as not enough key.only a thought like
xyzplasterer
New Member
Same here, this all goes back to my concerns over a wavy scratch. I use a 5 prong one.
I did a vertical scratch this time, same thickness and no cracks.
Ocr does not like going on to thick I'd avoid going above 16mm in 2 passes.
User___removed
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He said 10mm and more in places so if one pass that is probably the reason
Do you mind me asking why you hand balled instead of sprayed? Or was this before you got the machine mate?
xyzplasterer
New Member
Too small an area to use the machine on. Just so you know I don't Rend aid after dubbing out, I go straight over the sand/cement after dampening down. This job was a mix of existing sound scratch coat rend aided and dubbed out areas 4:1, no rend aid, no cracks.
My gut feeling is the cracks are caused by going on too thick.
My gut feeling is the cracks are caused by going on too thick.
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