I'm in the middle of redecorating and have found damp patches on the outer walls of my condo when I removed the wallpaper.

How do I go about fixing the problem so that new wallpaper can be applied?

Thanks in advance.

I take it that your condo is well above ground level hence it is not rising damp.

The damp possibly is from rainwater blown against and running down the walls seeping through by capilliary action. The only thing you can do to stop it is coat the outside surface with a heavy duty epoxy based (or similar) coating - paint. To be truly effective the entire exterior walls would have to be done - obviously outside your scope and budget.

The other approach is to contain it within the fabric of the wall itself and coat the internal surface with a waterproof coating before redecorating. Although this will provide a short term fix it will not be permanent.

The other possibility is that the moisture is seeping down the surface of the wall from the condo above you from a leaking water pipe or wastewater drain. Solution is to go up and check it out and persuade the occupants to repair the defective facility. Alternatively apply the second option as above.

If it's in a condo then it must be either rain water or water from another source dropping constantly on the outside, maybe an air con drain? Could also be a cracked pipe inside the wall, maybe not even your wall but one adjacent to it.

Either way the source of the water has to be traced and fixed before you proceed with your re decorating.

If the moisture is coming out of the wall, and likely it is, a good concrete sealer will fix it. Concrete sealer is water soluble and normally takes two coats. It is a white opaque color but dries clear. It provides good adhesion for paint so I would guess wall paper will stick to it quite well also. Any decent paint store should have it.

Thanks guys.

It's damp from rainwater as there is a ledge outside the window that must be collecting and holding the water on it.

I'll have to see if I can seal that as well where it joins to the wall.

If the moisture is coming out of the wall, and likely it is, a good concrete sealer will fix it. Concrete sealer is water soluble and normally takes two coats. It is a white opaque color but dries clear. It provides good adhesion for paint so I would guess wall paper will stick to it quite well also. Any decent paint store should have it.

Well in shopping for the sealer and epoxy I've found out that although the paint store may be decent the people that are selling the paint have absolutely no clue about what they are selling and what it's used for.

I did eventually get a satisfactory sealer but the epoxy is 'mai mi, next week' although I have found a roofing product that I'll give a try.