help with using emulsion over a stain block product

[maxit]

I replastered the walls couple of month ago, there was a what it seemed like a damp patch on the wall. After lots of inspection we could not find out what was causing it. I used stain block paint and it seemed to work. Now I wish to paint the walls with emulsion. I already have applied a mist coat, but the patch where I have used a stain block does not look ling ke its blending properly with its surrondings. Can you please advice me on how to remedy this problem.

 

[Zampa]

I t will probably be because its a different surface to the rest...it bounces the light off differently.

Plus the fact the the old emulsion will have darkened a little

Either line the wall and repaint if if problem one

Or blend the new colour into the old using a damp sponge for problem two

 

[maxit]

Thanks for your reply zampa,
Just to be more clear I have to add that three weeks ago I used the stain blocker on the bare plaster, and couple of days ago I started painting the wall by doing a mist coat(3 part Dulux super matt+1 part water). Now I can see a difinite diffeirence on the spot which stain block was used.

Stain block is white and I used a white matt for the mist coat, I just don't want to go ahead and put a basecoat in case it would make things worst.

I hope I've explained the problem better than my first post.

 

[Zampa]

I would go ahead now...stain block isnt very white anyway..can I presume you allowed the damp mark to dry before you put the stain block on?

Once coated you shouldnt see any difference colour wise.

Can you get a pic up at all?

 

[maxit]

Cheers Zampa,
Yep it was dry when I applied the stain block, although it was not damp but whenever it rained or it got very cold the patch would get darker.

I would take a photo tomorrow

 

[JohnD]

what is on the other side of the wall? is there by any chance a drainpipe or a brick with bad pointing?

 

[maxit]

The troubled patcht is above the blocked up fire place on the chimney breast near the ceiling. The previouse owner have always had problem with the same patch which they remedied by sticking a foil over it and then wall paper over it(fire place was in use then).
When I blocked it I installed a ventilation hatch, when the problem persisted I even got rid of the chimney on the roof.
I have rendered the outside wall(K-Rend). And there is not any pipe on that area, except the guttering which is in good condition.