1lb of cure is worth 10 tons of mold: DIY repair of a poorly sealed window? lots of photos herein

Question

Preface

I live in China. Construction is largely handled by unskilled migrants, and one cannot just call up a specialist contractor to fix a major issue.

Problem

I've got a window that was not properly sealed when the apartment was built, and which has become a major vector for mold and moisture. So much so that ice builds along the edges in the winter and water occasionally pools in the summer.

Task

Fix it myself, from the inside only, with tools and materials readily available at Home Depot-type stores. (i.e. - nothing too exotic)

Photos and Descriptions

The problem window (north facing, to make things even more "fun"

Window blueprint, somewhat to scale.

Mold and plaster damage around the left concrete column. Interior is to the left, exterior to the right. The plaster is about 2MM thick and applied directly to the concrete, with a latex interior paint double coat. I don't know what exact material was used to seal the window in place.

The plaster is steadily falling off the wall due to the damp.

More falling plaster...

Close-up of some of the damage.

Best course of action?

I figure there's no getting around stripping all the plaster off the wall around the window, and that's fine. The questions I have in mind are:

• does the concrete need a sealant before fresh plaster & paint are applied?
• can the window frame be effectively resealed from the inside only?
• is there hope for success? or will this always be a bastard unless we can find a competent renovator who can fly? (we're on the 4th floor)

EDIT - photo captions don't work? I've added them manually as paragraphs...

Answer 1

Andrew, excellent question and great photos. The problem is a bit complicated. I can see from the photos that the water migration is coming from the top, perhaps even above the top of your window. Anytime the plaster separates from a concrete base, it means the moisture is coming through the concrete, most likely from the out of doors in your case. Unfortunately the proper fix would have to be diagnosed and repaired outside at the source of the leak. Since you have no assess to the outside to explore and repair, the only mitigation to the problem from the inside would be to seal the concrete with a hydo-seal product such a Dri-loc sealer. I really think trying to replace the scratch and finish plaster coats will be a waste of time and fail again soon. I would strip away all the plaster to bare concrete in the effected area, making a clean line at the end of the bad plaster. Attempt to dry it as much as possible with a fan or fan forced heater. Something like a small box ceramic heater would be fine. Strip out as much of the caulking from around the window frame as possible. Paint the concrete with two coats of the Dri-loc sealer. Let it cure completely, recaulk the window frame with a Silicon/Acrylic paintable caulk. Paint the sealed surface with a recommended type of paint compatible with the sealer you select. You will not have as nice and smooth a surface as the original plaster, however, since you cannot stop the source of the water, the goal here is to simply stop it from entering your window bay.

Answer 2

Step 1 is to stop the water from getting into the structure. This will begin as an exterior issue. Compounding the issue is that it appears the problem may be starting above your apartment, either from the roof or another window above this. In the US, that would end up being a call to the apartment/building manager to fix their part first.