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Azuledos

Aug 7, 2011, 12:49 PM

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Interim roof waterproofing

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I have a design/construction question that I haven't seen addressed here previously. Sparks' “The rain and my new roof” thread prompted me to write this. Any input on these issues would be really appreciated.

I've got a great floor plan for a small house to be built with regular Mexican techniques. It will be masonry block construction with regular infill posts of reinforced concrete (castillos) and horizontal tie members (dalas, vigas). The planta baja will be liveable but without too much extra space, so the plan is to allow for an ultimate second story for guest bedrooms, etc, but that will follow at a later date. We'll make sure the building is designed to support another level, and will extend the castillo rebar, etc)

The questions I have deal with putting on the ground floor ceiling/roof, also reinforced concrete, which will ultimately be the floor of the upper level. What's the best technique for waterproofing that surface and allowing for rain runoff in the interim years before the structure grows taller? Seems like the options are:

1) Construct the roof flat and seal the bejeezus out of it, and hope we remain dry inside until the next phase of construction starts.
2) Construct a flat roof surface, but apply an additional cap of concrete (perhaps using lightweight aggregate) slightly thicker along a “ridgeline” – creating a slight slope so the rain runs off quickly. Sealing would be easier, since there never would be standing water puddles, due to the slope.
3) Construct a flat roof surface and instead of multicoat sealing, erect a short sloped framework structure on top of the slab, and attach a corrugated sheet metal temporary roof, which could later be sold or recycled. Oh, and pray every time the wind blows hard.

Are there any other ideas? Which is the least cost or “best” option? A few more related questions...

Is lightweight aggregate concrete an option that would work for the additional cap coat?
Does the sealer make it difficult to adhere new concrete when you go to the next construction phase?
Any techniques for removing the sealer if that's what has to happen?

Seems like it would be easier to float in additional fill to level all the primer piso floors, rather than to chop out & remove the sloping cap, assuming there's a technique for adhering the additional mud.

Oh, and we can't just throw a tarp over the structure for a few wet weeks, as rain is frequent in the area where we're thinking of building.

Dan

whynotwrite

Aug 7, 2011, 1:47 PM

Post #2 of 4 (2069 views)

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Re: [Azuledos] Interim roof waterproofing

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how long will it be before the second stage building takes place? 1 year, 5 years, more...?? In our house there is an "air" space between floors, filled with coarse sand, leaving an area for water and sewer pipes to be run...and worked on if need be.... at the cost of the tile upstairs. On top of this sand a layer of cement is poured to be used as a base for the floor tile. With 4 bedrooms and 3 full baths upstairs, pipes need to be run somewhere and this works out fine... even to the point where we had to take up the tile in the hall way to fix a water leak.
I have other buildings with flat roofs, poured 30 years ago, and designed to build up upon. Over the years I have had few problems even without a roof coating and we too see lots of rain. A good roof coating on a new, cured cement roof, free of dirt and age, would probably last a long time with a new coating every few years.

sparks

Aug 7, 2011, 4:16 PM

Post #3 of 4 (2057 views)

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Re: [Azuledos] Interim roof waterproofing

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It amazes me that neighbors with flat or slightly slanted roofs have zero or minimal leakage ... and theirs is only the slab with a cement wash. And here I see moisture coming thru in 3/4's of the house.

I too will build above someday but have no option at this point but to use impermeabilizante

Sparks Mexico - Sparks Costalegre

Bennie García

Aug 7, 2011, 5:42 PM

Post #4 of 4 (2043 views)

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Re: [Azuledos] Interim roof waterproofing

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I have used the method descibed by whynotwrite with the exception of using sand between the 2 layers of concrete, Sand is heavy, it is better to use jal (coarse pumice) which is a far lighter material . Then pour your subfloor on top of that.

In the meantime you can run a slight slope on the roof and future entrepiso. This can be leveled easily with the jal when it comes time to add the second floor. The concrete losa will have no problem adhering to this material because of its porousness.