Damp Patches on Wall of Converted Garage - Can I use Stain Block to Block Marks?

[vickeel]

Hi looking for some advice, previous owners converted garage as part of
the house.
Gone to decorate one of the rooms removed wallpaper and have found
dark patches where it looks as though they have dob and dabbed the
plasterboard.
Would it solve the problem if I water sealed the outside wall and used
damp block paint on the inside wall before redecorating.
Hope someone can help!

Vic Keel

[prothos.services]

Hi. As long as the garage has an adequate damp proof course, an external clear stone or brick sealer would definately prevent the damp returning. Make sure the gutters are draining properly, which may be the cause of the damp patches.
After sealing the wall i would recommend waiting a week before sealing the internal wall to ensure any water in the wall can escape, otherwise the water will just make the coating fail over time.
A clear impregnating sealer such Isonit Hydroblock would do the trick.