Hi,

I'm new here, signed up as I'm planning on building an adobe house or something similar next year and wanted to get some advice.

So to begin with I'm living in Cusco, Peru which is part of why I want to go with adobe.

Being in Peru you'd think that there would be expert advice on how to build an adobe home but the builders here are complete cowboys so I'm going to get some outside advice and then take a blend of the two.

So my questions are:

1: Typically rubble trench foundations are used here, the rocks used are typically 12-15" in size, is that normal?

2: Concrete slabs are not used as part of the foundation and no drainage pipes are put in. Are these a necessary part of the foundation? If concrete slabs are necessary is the rebarring a necessary part and what is it for?

3: The trench depth is recommended to be 4" below the frostline. Where I'm planning on building is very warm, frosts don't happen. What depth should the foundations be?

4: The area is earthquake prone. Typically earthquakes don't get beyond 3-4 richters but every few hundred years they get a big one. Luckily it's not due for another 250 years but I don't know how many larger earthquakes they get in between. I have seen several adobe buildings that are hundreds of years old that have survived at least 2 major earthquakes but is concrete going to stand up better?

5: Does anyone know how high you should build adobe walls? Here they don't recommend over 2 stories but I think I read somewhere that one story houses survive earthquakes better. I'm thinking one and a half stories with the end walls raised to 2 stories to support the roof.

I think that is all for now, any general tips on things consider will be appreciated as well. Thanks in advance for your help.

Hello,
I have been to Cuzco, and took the train to Machu Picchu.  It was wonderful!

Do you have access to Portland Cement?  Good clay?  An electric portable concrete mixer?  Here is my recipe for adobe.  There are a number of people in this area that use this recipe.  However, it's not an exact science, as clay can vary in it's sand content in different areas.  The main thing is that it's pretty sticky.  It should adhere to a vertical wall easily.

4 Shovels Masonry Sand
3 Shovels Clay
2 Heaping Handfuls of Straw (we go a little extra).
1-2 Gallons of water (varies based on the dryness of the sand and clay).

We usually mix a triple batch in the concrete mixer at one time.  For outdoor applications, you're supposed to add 1:12 of Portland cement.  So we just add 2 shovels to the triple batch.  I'd rather have a little too much cement.  Mix the clay dry components first.  If very dry, you may want to lightly spray in some water, so you don't breathe in all that silica.  Add the Portland cement, and fold it in, as it likes to float atop the other dry ingredients in the mixer.   Mix, fold, mix, fold.  Then add water to consistency.  Think joint compound, if you know what that is.

We've been using this mix outside, and then, a few days later, after dry, we've been covering it with a 1/4" of concrete mix.  Last night we had a heavy rain, and we thought the exposed adobe (with no concrete covering) might be washed away, but it was perfectly intact.  Note: This is a vertical wall.

For the indoors, there are 3 other ingredients that we add to the above recipe:
3 oz. Lime Powder (workability).
3 oz. Dry Wheat Paste (we've been using 3 oz of wallpaper glue, as we can no longer find wheat paste).
1-1/2 oz. Borax (mold prevention).  This may be tough to find in Peru.  Maybe they have something similar.

Good luck with your project!

Some others may chime in on the earthquake portion, and anything else, as I've only built one house.  Typically, foundations are 30" minimum depth, for freeze protection.  I'd still go with this, even in the warm climate.  It may help if there is a tremor.  If you're using stone, you would probably want to use concrete in the joints.  If you're using all concrete, you'll want to add some rebar.  Typically, you'd put j-bolts in the concrete, to attach to your footers and framing.  If stone, you could probably put those in the concrete joints.

A French drain would help, around the perimeter, with a couple layers of poly below grade over the foundation, and down to the drain, to avoid moisture seepage into your foundation.  You can google this.

Also, do you have access to black paper?  Diamond mesh (or chicken wire)?  Pneumatic stapler?

Over your decking (plywood?), staple black paper or tar-paper.  Use a pneumatic stapler to attach the diamond mesh.  This should be tight, so don't scrimp on the staples.  Adobe over this.