Painting Over Damp Stain

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I have a damp stain caused by crack on exterior wall which I've sorted out and now im left with the damp looking stain to sort out.

What do you all recommend I do to tackle this issue in terms of sanding down and what type of paints I need for the job?

Thanks.
 
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You can either cover it with oil based undercoat, or use a more modern equivalent like this. Then you paint as normal once it's dry.
 
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oil based undercoat is the old way there are better products out there now, the screwfix stuff is OK and can work I have used it plenty of times, it's probably better than the undercoat. If the stain is quite severe/maybe still a bit damp then something like Zinsser BIN, which contains shellac might be needed or even Zinsser Gardz which will cover just about anything
 
oil based undercoat is the old way there are better products out there now, the screwfix stuff is OK and can work I have used it plenty of times, it's probably better than the undercoat. If the stain is quite severe/maybe still a bit damp then something like Zinsser BIN, which contains shellac might be needed or even Zinsser Gardz which will cover just about anything

I've tried the Zinsser BIN in the past and I applied it to the wall when on the bare plaster after I sanded it back and I found that when I then applied two coats of the coloured matt paint which is Dulux 'Timeless' which is a slighly off white and it wouldn't paint over the Zinsser BIN without it showing through.

Did I do something wrong?
 
how many coats, as it is shellac based it does dry a bit shiny and can take a few coats to stop the sheen showing through.
 
how many coats, as it is shellac based it does dry a bit shiny and can take a few coats to stop the sheen showing through.

I only gave it one coat.

What about using Zinsser 123 as it sounds like it has similar stuff to the BIN but its water based not oil or am I just better off using an oil based undercoat?
 
If it is just a stain and completely dried out then 123 would probably sort it. As for your previous attempt one coat of emulsion really isn't enough stain or no stain
 
If it is just a stain and completely dried out then 123 would probably sort it. As for your previous attempt one coat of emulsion really isn't enough stain or no stain

the wall is still a bit damp.

Am I better off in this case to use an oil based undercoat or the spray you mentioned then a couple of coats of emulsion to sort it out?
 
your best bet would be to let it dry some more, at least until it feels dry on the surface then I would use BIN to be sure
 

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