Preventing Mold in alternative building with Magnesium Oxide

Lots of alternative construction and regular construction have issues with mold and black mold. I have read that the use of Magnesium Oxide (MgO) in the mortar will effectively prevent this in brick/rock wall construction and in cob and earthen materials construction. The sources for the MgO can be animal manures or commercial. 1. Does anyone know what the ratio is of manure (horses are what I have) to the rest of the blend in cob or CEB to effectively get the properties of the MgO? 2. Does anyone know whether the effectiveness for this purpose and for the purpose of reducing heat transfer using MgO is working for them?
I am familiar with the rest of the best practices stuff of good drainage and a high enough rock wall before placing the cob, etc., but I am interested to know if others have seen and found out more of the use of MgO to effectively prevent mold in alternative construction in humid climates like here in SW WI. Black mold, being a serious health concern for its neurotoxicity, is something I have seen way too much of in the alternative building sites I have seen and/or heard about.

Manure seems like the perfect mold food to me. Are you sure the MgO benefits would overcome the increased mold food potential?

I think most mold problems are the result of poor water management; improper flashing. Be sure to flash your windows and transition with best practices.

Thanks for the feedback Springtime Homes. One would think that the manure would be a good food for the mold, so I was also taken by surprise to read that it was the source of MgO in ancient cement and earthen structures. Something about the MgO assisting in moisture transfer (Kinda like wool does) seems to be the dynamics I remember reading but on the order of balancing the indoor and outdoor humidity such that indoor humidity does not get trapped. This is about the most information I have been able to find thus far: http://www.geoswan.com/assets/MgO-GENERAL.pdf I thought I would put it out there to see if more research has already been done and to ask if others are willing to share.

I went back to read the above posted article and see that I got the chemistry wrong when it comes to the use of manures in earthen structures and MgO cement. Here is a line from the article:

"Phosphates are available from many
sources ranging from phosphoric rock to animal wastes and fermented plants, which
historically were used to “react” with various oxides to produce these environmentally
friendly, non-toxic cements."

Traditional English cob homes get around this by plastering with a mixture with lots of lime. If you don't want lime-white walls you might throw in some natural coloring and a bit of clay to bring it more into an earth tone. From my understanding molds and fungi can't deal with lime.

The other thing about mold is your foundation. If you've built a bad foundation you'll have mold problems. This is the case with ANY house. In the case of cob, you'll want to trench your outside walls and lay down a foot or two of gravel in your trenches, then build up on that with stone or something that won't soak up groundwater at least a foot . Then start in with the cob. Big eaves also help.

All that is good information, Marcus. I am also interested to know if any have done research on MgO and have any experience with it.

Check out Hemp Adobe Homes on youtube and their website. He claims it is so good it heals itself if it is cracked because it draws in carbon. Very futuristic stuff yet simple and it sets up in 2 minutes! I don't think you really need the hemp because its the Magnesium Oxide and the Phosphate that does the trick. Portland cement wont bond with cellulose but this will. So you could use straw and wood chips and it would be more insulating, stronger and lighter. In ancient times I guess the manure was a source for it to bond with and it had the phosphate necessary to set up with the MgO. If I had the money I'd experiment myself on ratios of what to put in and such.
Here is a source apparently for Magnesium Oxide https://www.uswatersystems.com/flomag-magnesium-oxide-media-corsex.html?fee=10&fep=1728&gclid=CNaki5L9oMsCFQ6oaQodTmkMfA

I've heard ashes are used in certain quantities but for what reason I don't know. If anyone finds out the ratios of MgO, straw/woodchips and manure or a different phosphate source please share!!!

Greetings!
I run a Learning Center in Blanco, Texas and we have used MgO in our stucco for finishing, our floors (sub -floor and finish) and eventually used a combination of hemp hurd and MgO (Hempesium) to build wall systems (cast-in-place).  We have built three cast-in-place structures here.  The first was a hempcrete building (hemp and lime) building that we had mold issues with.  We tore out the effected areas and built back with our MgO and Hemp mixture and resolved the issues.

We also had some moldy hemp so used it to make some blocks and when sliced open a few months later there was no evidence of any mold!

Our most recent build was the Hempesium project and I cannot say enough good things about the outcome!  
It is fire proof, mold and bug proof, highly insulative and increases the strength of the wall itself.  It is a low cost, natural, non-toxic combination of materials with a (better than) net zero impact on the atmosphere!
If anyone would like to see pics text me at 830-383-5272.
Jennifer Bailey