Homemade stucco for earthbag exterior

I am very new to all of this and do not have any background in construction, so my question is perhaps simple and yet my phrasing could very well be quite off. In trying to stay under a very small budget, I am trying to make my own stucco cement for an exterior wall of an earthbag dome in New York State. I believe this climate is humid/rainy enough that I will have to choose waterproofing over breathability when it comes to the walls, thus I am thinking a three-coat stucco system. So,
1) I found a "recipe" for stucco that is about 25:2:1 in sand:cement:lime, but it seems like concrete is more abundant and cheaper than buying Portland cement, and that concrete is basically mostly Portland cement and sand/gravel anyway. Could I use concrete instead of cement and just lower the ratio of sand?
2) Do I need a finishing coat, on top of the scratch and brown coat? I don't care much about the outside appearance at this point in my finances.
3) Are there any recommendations for a cheaper exterior coating? Building codes are not relevant, I just need something that will inhibit leaks and not lead to mold problems or compromise the dome structure.
Thank you!

Georgie, for the outer walls follow this guide from the National Lime Association: Table 2 Type S and the mixing procedure below: http://lime.org/documents/publications/free_downloads/fact-masonry.pdf

You'll end up with a stucco that is both breathable and water resistant. Cement is Portland Cement(OPC) and it's purpose is to speed drying time, so if it is humid the day applying add more. If it is dry add less and keep hydrating for about 30 days to allow the lime to gain max strength. Otherwise OPC is not needed. Lime is far more resilient and stronger than earth as an exterior stucco. Earth is best on interior walls, especially in cold-wet climates like NY.

As far as the domed roof I'd need to see what that looks like, seams, spans, etc...

Georgie Treesdale wrote: I am very new to all of this and do not have any background in construction, so my question is perhaps simple and yet my phrasing could very well be quite off. In trying to stay under a very small budget, I am trying to make my own stucco cement for an exterior wall of an earthbag dome in New York State. I believe this climate is humid/rainy enough that I will have to choose waterproofing over breathability when it comes to the walls, thus I am thinking a three-coat stucco system. So,
1) I found a "recipe" for stucco that is about 25:2:1 in sand:cement:lime, but it seems like concrete is more abundant and cheaper than buying Portland cement, and that concrete is basically mostly Portland cement and sand/gravel anyway. Could I use concrete instead of cement and just lower the ratio of sand?

Stucco has no need for gravel and in fact gravel will make it hard to put on since the larger than sand stones will be points of departure on a vertical wall, it is actually better to use Portland when making stucco, the premix concrete will not perform well as a substitute material.

2) Do I need a finishing coat, on top of the scratch and brown coat? I don't care much about the outside appearance at this point in my finances.

The purpose of a scratch coat is to give the cover coat a better holding surface and to start the smoothing of the finish coat, so yes if you want a durable, good looking, water repellent stucco job you will need to do at least a scratch coat and finish coat.
Earth Bags are usually covered with an earthen stucco, but you can use "regular" stucco since both would hold best when a backer mesh is used for the scratch coat to bite into.

3) Are there any recommendations for a cheaper exterior coating? Building codes are not relevant, I just need something that will inhibit leaks and not lead to mold problems or compromise the dome structure.
Thank you!

The cheapest exterior coating would be earthen plaster. earthen plaster, when correctly mixed, applied and cured is very water resistant. For best results of any stucco type coating you would want to use a mixer so everything is fully incorporated, it also lets you make additions and see the result of that addition a lot faster than using a tray and trowel (hoe) mixing method.

Scratch coat, 18 shovels of sand to 1/4 sack of hydrated and 1 sack of portland cement. Brown coat is 21 shovels of sand, 1/4 sack lime and 1 sack cement. Finish coat is 2 1/2 sacks dolomite (limestone) sand, 1 sack lime and 1 sack cement. For more durable finish, cut down the lime to 1/2 sack. I'm giving the recipes for the 3 coat stucco because you asked, not because I'm saying it is the system you should use.

I saw a video of some English plasterers making a water proof lime wash for exterior stucco with slaked lime and tallow. Seemed like a sweet idea. I would advise against using chemical or synthetic products to waterproof in a wet environment, you will just end up with condensation and mold inside. Think about it the best winter gear is engineered to be breathable and warm, so I would not associate the porosity of the stucco with letting in cold and moisture, cold maybe, wet I would be surprised if that much water vapor could make it through the plaster stucco.

Stucco is NOT waterproof.  IT's basically cement, which is porous.

This is why code requires a waterproof membrane under stucco... usually some sort of waterproof "wrap".

I've seen earth bag homes that were "smoothed out", then covered with a waterproofing, like plastic, tar paper, whatever, then covered again with more of the cob/earth stucco material.
Cal earth does it this way as well.  They cover the waterproofing with "balls" of cob, they call "reptile scales"  Look at Calearth.org for info..,

Eddie Conna wrote:Stucco is NOT waterproof.  IT's basically cement, which is porous.

This is why code requires a waterproof membrane under stucco... usually some sort of waterproof "wrap".

I've seen earth bag homes that were "smoothed out", then covered with a waterproofing, like plastic, tar paper, whatever, then covered again with more of the cob/earth stucco material.
Cal earth does it this way as well.  They cover the waterproofing with "balls" of cob, they call "reptile scales"  Look at Calearth.org for info..,

Wouldn't the poly woven bags be considered a vapor barrier?

Steve Harvey wrote:

Eddie Conna wrote:Stucco is NOT waterproof.  IT's basically cement, which is porous.

This is why code requires a waterproof membrane under stucco... usually some sort of waterproof "wrap".

I've seen earth bag homes that were "smoothed out", then covered with a waterproofing, like plastic, tar paper, whatever, then covered again with more of the cob/earth stucco material.
Cal earth does it this way as well.  They cover the waterproofing with "balls" of cob, they call "reptile scales"  Look at Calearth.org for info..,

Wouldn't the poly woven bags be considered a vapor barrier?

Not with the gaps between them where water can get in.  Waterproofing is usually done in a sheet, or overlapping sheets of some sort of waterproof material.  

In Earthbag construction, Bags are stacked, leaving gaps between them, where water can accumulate, and then start causing damage.  

If you're in an area with freezing temps, that water can get in, freeze, expand, and quickly destroy whatever you built.  Like in a few years, the structure could be rendered unsound.    

Even without freezing temps, a house with wet walls will grow mold, mildew, etc.  Not a deathly living situation.

WATER is one of the biggest enemies of any type of construction.  Proper waterproofing, and drainage, in ANY construction is vital for long term success.  Waterproofing shouldn't cost much, but it does take time.  

or don't do it, take one's chances, and likely suffer the consequences...