Putting an End to Leaking Roofs on Apartment Garages

Question: We purchased a new apartment building a year ago. The apartments are above a subterranean garage that extends under the entire apartment structure. The first floor slab (subterranean garage ceiling) is exposed to weather as it is not enclosed with a roof. We are trying to decide on a product that will provide us with good waterproofing to elminate water dripping on vehicles when it rains as well as aproduct that will be low maintenance. What do you suggest?

Answer: Walter F. Pruter of W. F. Pruter Associates, 3127 Los Feliz Blvd., a construction technical consultant, handled this one for me. I put him in touch with the reader and he will send her full details.

First of all, weather-exposed surfaces must be constructed to make water drain away from the building, he said. In your case, he said to make sure that exposed deck and/or porch slabs slope away from the exterior walls.

Assuming the deck-ceiling slab is cast-in-place concrete poured dead level, or--worse--sloping towards the building, Pruter recommends that proper drainage be achieved by placing a new fill on top of the old slab.

There are proprietary products for this or a good concrete repair contractor can prepare a mix on the job, Even in a thin application, this mix will adhere to the existing substrate without excessive cracking or flaking, he said.

"Obviously, any materials presently on the deck--paints, coatings or sealants--that could adversely affect the bond of newly placed material, must be removed," he said. "Bond failure of new concrete to old isn't always the result of inadequate adhesion: it is often caused by shrinkage in the new concrete."

He recommends checking a publication called the Concrete Sourcebook, published by Concrete Construction Publications Inc., 426 S. Westgate, Addison, Ill. 60101-9929, for names of firms marketing waterproof coatings and toppings for roofs and decks. The October, 1984, issue of Concrete Construction magazine has an article on concrete repair materials that Pruter believes is worth reading.

Specialized publications like the ones he mentioned can be found in large public libraries--either the central library or a large regional branch in the case of the Los Angeles system.

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