Papirex
Oct 6, 2004, 5:42 PM
Post #5 of 9
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Re: [Nancy Boyd] Water proofing an underground casita
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Esteban has told you the only way that you can be assured that the walls will be waterproof. Since the casita is underground, the roof must be waterproofed too. Anything you put on the walls from the inside will just be a temporary patch, and will eventually fail, if it works at all. The drainage pipe around the building is extremely important. I spent my life in the construction industry, and anything underground is entirely different than above ground construction. It usually requires some engineering for the specific location. Remember, an architect is not an engineer.
We used to live in Alaska. Many houses up there have what is called locally a “daylight basement.” That is a basement that is only half underground, and half above ground. There are a couple of reasons for building them that way. It allows you to have windows in the basement, and it reduces the likelihood that the walls will leak as the hydrostatic pressure on them is less than it would be if they were fully underground. It is also good practice, and required by some building codes nob to put a waterproof membrane under any floor slab that is poured on grade (on the ground.)
There are a few contractors in Anchorage that have a specialty of waterproofing those walls when they start leaking, as many building contractors will take the shortcut of not waterproofing them during the house’s construction phase.. I have seen them do it, after they excavate them, they mop the outside of the walls with what looks like roofing tar. It may be coal tar, I don’t know, they look the same. Coal tar is different chemically, more brittle, and more permanent. It is extremely important that the outside of the walls be thoroughly cleaned before any waterproofing is applied, otherwise it will probably not bond to the walls and may fail. If the walls are rough stone, or brick, and were not plastered, it will be more difficult to apply an effective coat of waterproofing.
We leased a house our first year here in Cuernavaca that had a maids quarters built in to a hillside. The back wall leaked lots of water during the rainy season. For geologic reasons the only solution I could see was to destroy the casita, and rebuild it correctly. We didn’t have a live in Maid, and only used it as a guest room. I would never buy any house in Mexico that had anything underground unless I knew the builder, or could see pictures of the house under construction.
If it were me, I would break up the terrace as needed, do the excavation and waterproof the walls and roof now. It won’t be any easier, or cheaper to do it later. There are a lot of the laws of physics that should be understood before attempting any building project. Even something as simple as a house. Many do it yourself builders are unaware of them, or ignore them. You can ignore all the laws of physics if you want to. One thing you can bet the rent on, is that the laws of physics will not ignore your project.
Rex
"The supreme happiness of life is the conviction that we are loved" - Victor Hugo
(This post was edited by RexC on Oct 6, 2004, 7:54 PM)
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