Black streaks on external render

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Rturner

Guest
Ur a cock anyway so even If I did I wudnt say..:)
Hope u find the answear ur looking for
Obviously not from an ignorant T@@t who's got no idea, but is happy to post insults to a thread asking for assistance instead of providing it.
 

Deri

Active Member
Poo
 

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Deri

Active Member
You don't need a lot just a bit in a couple of mixes and it seems to be all over the wall.
 
R

Rturner

Guest
You don't need a lot just a bit in a couple of mixes and it seems to be all over the wall.
It is all over three walls, 60 sq meters so it'd have to be in every one of the mixes start to finish and the mixer was washed out between each mix so there wasn't any carry over. I know cos I did all the mixing for the guy spreading it. Unless it had been incorporated at the quarry before the sand was put in the dumpy bag I can't see how this could be the reason.
Though I'm grateful for any suggestion.
 

Rigsby

TPF Special Forces
I have had contaminated sand. It is not the quarry in my case but the tipper lorry not cleaning out his previous load. I have had limestone, top soil,other sand. Then at this time of year I have had leafs from the trees that overhang the sand pit in the merchants yard.

Cats seem to come nightly and bury there poo. So can become daily. On the job I had the problem it was 3 ton dropped on the ground and was there for a while.
 

plasterjfe

Private Member
Sounds like the sand but admixes can sometimes bleed out in spots.

What age property and wall type ? Solid,cavity etc
 
R

Rturner

Guest
It's a new extension , block cavity, as I said previously the scratch coat using 50/50 didn't have a problem, it's just the whole top coat with washed yellow sand that has the problem. The admix was liquid and well diluted, the sand was delivered in a new dumpy bag and kept covered.
 

Vincey

Private Member
It's a new extension , block cavity, as I said previously the scratch coat using 50/50 didn't have a problem, it's just the whole top coat with washed yellow sand that has the problem. The admix was liquid and well diluted, the sand was delivered in a new dumpy bag and kept covered.
Was just talking to my mate about these spots he been rendering for 40 years,showed him picture and he said looks like particles of rust from inside cement mixer? Had similar with a his old one before got the new one, could you post up a picture of the whole side hopefully he can help, also he said sand tex paint has stabiliser that probably to late to put on now ,usually goes on before sandtex paint on dusty type backgrounds
 
R

Rturner

Guest
I can see the thinking... But no it's not a rusty mixer. This one was acid cleaned before the start of the build and had 5 dumpys of gravel and sand through it before we got to this stage so it's nice and clean inside. I'll try to get a better picture of the wall but it's pretty awful outside at the moment.
Whatever it is, it seems to be small 3-4mm blobs which dissolve and then bleed out leaving a streak and a tiny hole.
It's really weird and polluted sand seems to be the most likely cause, the problem is, it's on there now so how is the best way to treat it?
And just to be clear, I provided labouring and materials to save costs, I didn't apply the render, contrary to others views, not in my skill set...
 

theshed

Well-Known Member
I can see the thinking... But no it's not a rusty mixer. This one was acid cleaned before the start of the build and had 5 dumpys of gravel and sand through it before we got to this stage so it's nice and clean inside. I'll try to get a better picture of the wall but it's pretty awful outside at the moment.
Whatever it is, it seems to be small 3-4mm blobs which dissolve and then bleed out leaving a streak and a tiny hole.
It's really weird and polluted sand seems to be the most likely cause, the problem is, it's on there now so how is the best way to treat it?
And just to be clear, I provided labouring and materials to save costs, I didn't apply the render, contrary to others views, not in my skill set...
You can get a cordless and drill them out and fill.
 

jamesthefirst

Private Member
In an ideal world you could remove one of the spots and have it tested then go from there. I like to watch medical detectives on sky can you tell? :)
 

duke163

Well-Known Member
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?
Just seen this while reading about something else ; Alkali resisting primer is mainly for use when you are intending putting an ordinary oil based paint as the finish coat over new plaster or rendering..it prevents the alkali in the surface attacking the oil in the paint and causing 'alakli burn' or saponification...which turns the oil into a sticky brown soap like sustance.
I don't know if this helps at all .
 
R

Rturner

Guest
Just seen this while reading about something else ; Alkali resisting primer is mainly for use when you are intending putting an ordinary oil based paint as the finish coat over new plaster or rendering..it prevents the alkali in the surface attacking the oil in the paint and causing 'alakli burn' or saponification...which turns the oil into a sticky brown soap like sustance.
I don't know if this helps at all .
Thanks, the little blobs were there before the paint was applied, which was weathershield, which isn't oil based.
 

zolco

Private Member
Thanks, the little blobs were there before the paint was applied, which was weathershield, which isn't oil based.
Try zinsser stain block or go the old fashioned way, gloss it then put the weathershield over it. I doubt your merchant will reimburse you if that's what you looking for.
 

zombie

Private Member
Get a renderer to put a tight bucket coat 1.5mm silicone over the top once primed

Saves the need to paint
 

dieselpower

Active Member
Thanks, the little blobs were there before the paint was applied, which was weathershield, which isn't oil based.

Definitely s**t sand, that's what happens when you buy jewson bulk bags up here in the stix, keyline also, hence I don't use their crap...
 

theclemo

Private Member
It's the cement not the sand. Can't believe that wasn't said by now. And I'd blame u and the builder for letting u mix. The fix is easy. Take off do again. Or find some kind of stain cover to paint on the cement dots b4 u paint. Best of luck.
 

jet

Active Member
Had this on a small render job a Few years ago .
It was oil in sand ...

There were 2 0r 3 spots high on elevation
I just used 5mm masoanry bit to drill them , out filled hole no problems
 
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