Treating Walls for Interior Condensation
Kitchen and bathroom walls that run with water are the result of a natural occurrence. When water is heated it becomes steam, which expands and rises to meet the cold upper surfaces of walls and ceilings, where it condenses and is reformed into water which streams down the wall, or gently weeps, according to the cubic capacity of the room and the amount of steam generated. The process can be simulated by holding a cold dinner plate in front of the spout of a steaming kettle — the colder the surface the quicker condensation is set up. In a bathroom the mirror always shows the first signs of condensation; this is because the surface is cold and the mirror is non-absorbent.
Kitchen and bathroom walls are usually tiled or coated with gloss paint which makes the surfaces non-absorbent and aggravates the condition. If wall surfaces in steamy rooms are coated with semi-porous materials, such as distemper or emulsion paint, condensation will be reduced but not eliminated. Opening the windows and doors of steamy rooms cuts down the amount of condensation, but this is not always convenient and the steam may spread to other parts of the house, where it will attack wallpaper, ceilings, metal fittings and furniture.
There is no type of wall covering which is completely steam-absorbent; there is, however, a paint mixed with fine cork granules which is specially manufactured for the walls and ceilings of steamy rooms, but use of this paint does not cure the condition completely. The condition may be alleviated to a limited extent by providing ventilation to the room – fitting one of the top panes of a window in the steamy room with an adjustable vent, of which there are many different kinds. A small extraction fan of the ventaxia type may be fitted high in the wall of the steamy room, and this will considerably reduce the nuisance, but this may be found costly and there is a much easier way of dealing with the condition.
Rising steam accumulates in the top of a room where it remains as a bank of moisture-impregnated air until it disperses by condensation in contact with cooler ceiling and wall surfaces. Dispersion may be accelerated by providing an outlet and by cooling the upper air of the room. This may be done by inserting an air grating in the outer wall of the affected room; two gratings are better than one; the gratings should be inserted with tops about 3 in. below the ceiling, near the corners of the room. The positions are shown in the image (see below), which illustrates the placing of the two gratings in a room with one outside wall, and in a room with two outside walls.
The gratings, which are of galvanized steel, are 9 in. long by 3 in. deep, which is the size of a brick, and to fit them it will be necessary to remove one brick from the inside wall and a corresponding brick from the outside wall. The position of the brick courses may be ascertained by measuring from a window; the outer and inner bricks are removed by raking out the mortar from the joints round each brick, with a thin brick chisel and an oldblade. Before replacing the bricks removed for the metal gratings, one in the outside wall and one inside the room, it will be necessary to line the cavity with pieces of slate see image – wall gratings), cut so that the top piece rests on the edges of the side-pieces.
This is done to prevent stale air circulating in the wall cavity from entering the kitchen or bathroom. The cavity lining may be secured in place with a thin mortar compounded of one part Portland cement to three parts of sand, and mixed with water. The metal grids are fitted with a prong at each corner (see image – wall gratings), and the grids should fit tightly into the corners of the cavity, where they are bedded into a small amount of the cement-mortar. Make good surrounding wall surfaces, as explained in the on Interior Decorating, after fitting the inner and outer gratings.
This will be found the most effective cure for steamy rooms. If the new gratings create an uncomfortable draught this may be counteracted by fitting a boxed vent over the inside of the gratings. The construction of a simple box vent is illustrated above. The front isor 1/8-in. ; the wedge-shaped sides are 3/4in. , sloped from a point to a 2-in. Top opening. The length of the box should be longer than the grating to accommodate thin battens screwed into the plugged walls at the ends of the grill.
Ground floor rooms can be fitted with floor grilles to provide further ventilation.