Black streaks on external render

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Rturner

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we had a general builder two coat render our extension. The final coat was with what was supposed to be washed yellow sand. As it dried out small black blobs appeared which ran down the outside. These are still appearing through the final Weathershield paint finish.
He thought it might be oil contamination in the sand but it seems to be water soluble...
Has anyone come across this before and is there a way to deal with it?
 
Rturner said:
we had a general builder two coat render our extension. The final coat was with what was supposed to be washed yellow sand. As it dried out small black blobs appeared which ran down the outside. These are still appearing through the final Weathershield paint finish.
He thought it might be oil contamination in the sand but it seems to be water soluble...
Has anyone come across this before and is there a way to deal with it?
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It is caused by plant root in the sand. If you are painting it do worry leave it until the black die stops running. It won't affect the finished job, it is very common in sand in the south of England.
 
Thanks for the replies... I think I'm inclined to agree with the plant root theory. It's obviously water soluble and has been broken up in the spreading process so bleeds out when it gets rained on. I'll let it alone for a while to see what happens and then try the Zinnser if it needs it. The merchant that sold me the S**t sand will get a visit...
 
And how would you sort this out then? Perhaps you could offer some positive advice?
 
Rturner said:
And how would you sort this out then? Perhaps you could offer some positive advice?
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Apologies if it sounds negative,can you post a few pictures up of the job as a whole ? From original post you said see black spots before painted is that correct? If yes why did he paint?
 
Without seeing it, I'd suggest it's dirty sand. If it washes off I think it'll probably wash out in time. Don't think there's a lot you can do other than keep cleaning it.
 
theplasterman said:
Apologies if it sounds negative,can you post a few pictures up of the job as a whole ? From original post you said see black spots before painted is that correct? If yes why did he paint?
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The day after the top coat there were loads of these little weeping black blobs. They washed off in the rain, we thought they'd all gone but after two weeks I painted it and now a week later a few are still showing through. If it is dirty sand then it's the merchants responsibility as I specifically ordered washed yellow plastering sand.
image.jpeg
 
i have seen stains like that when powdered feb mix has been used. if the feb gets wet , and not used for a while it sets in little lumps and bleed through the finish.
 
malc said:
i have seen stains like that when powdered feb mix has been used. if the feb gets wet , and not used for a while it sets in little lumps and bleed through the finish.
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We only used sand, cement and liquid waterproofer, which was well dissolved in the water. The same batch of cement and proofer was used in the scratch coat but different sand, a course 50/50 mix. This didn't have the stains...which points to the yellow sand
 
Maybe general building sand was used and not washed plastering sand.
I've seen cat s##t in the sand do similar too.
 
Deri said:
Maybe general building sand was used and not washed plastering sand.
I've seen cat s##t in the sand do similar too.
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Though the dumpy bag clearly said washed I suspect it wasn't, if it was cat crap then it was all the way through 900kg and that's a hell of a moggy someone's got there
 
Rturner said:
We only used sand, cement and liquid waterproofer, which was well dissolved in the water. The same batch of cement and proofer was used in the scratch coat but different sand, a course 50/50 mix. This didn't have the stains...which points to the yellow sand
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you would have to use a feb type of additive. a mix of sand, cement with a waterproof additive would be dead and unusable.
 
The waterproofer also contains air entrainment so no it wasn't dead at all
 
Rturner said:
We only used sand, cement and liquid waterproofer, which was well dissolved in the water. The same batch of cement and proofer was used in the scratch coat but different sand, a course 50/50 mix. This didn't have the stains...which points to the yellow sand
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"We only used" you rendered that yourself didn't you?
 
malc said:
you would have to use a feb type of additive. a mix of sand, cement with a waterproof additive would be dead and unusable.
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I have been using this. It has plasticiser in it. Creams up great when it has a good spin. Great stuff.
 

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stuart23 said:
"We only used" you rendered that yourself didn't you?
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I was reading down thread and thought exactly same..this is the spread who has rendered it asking for advice..y dsnt he just ask instead of being a client lol..cn tell he's the spread as he got all defensive wen Vince said get the guy bk who rendered it..
 
stuart23 said:
"We only used" you rendered that yourself didn't you?
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Wrong conclusion!!!
I mixed for him that's all, so no I didn't render it myself and no I'm not a skim looking for an answer. I employed a well respected local builder who also happens to be good at rendering and skimming. I was a chippy years ago so I cut and tiled the roof.
And "all defensive" is wrong too. It's a fault in the materials not his workmanship that's the issue and why I thought there might be someone professional enough to give us a clue. As it happens I think there was one.
Yes the waterproofer is the red goo and yes it does come up creamy with a good mix.
 
Shite sand end of.
Funny that the guy that done it pretends to be the client though [emoji23]
Then doesn't reappear


Sent from my iPhone using Tapatalk
 
BigK said:
Shite sand end of.
Funny that the guy that done it pretends to be the client though [emoji23]
Then doesn't reappear


Sent from my iPhone using Tapatalk
Click to expand...
I am the client, and no I didn't pretend that I did it...
 
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