Rain against the outside walls?

Even with good overhangs, rain can get blown sideways and be raining against the side of a house. How does this effect cob? If there's a week of hard rain, blowing against the outer walls - does this cause problems? How can you prevent problems from this?

Hello Sahara,

You are correct, but in better designs this effect is at a minimum. In general, unless you are speaking of a two story structure, the eaves should protect the side walls, and the wet weather should strike at approximately knee wall height, and below. In better designs the knee wall is in stone.

Most importantly, to all of this, is the rendering the should (must?) go onto the building, be this a clay, or lime plaster. It can even be a rain screen wall of wood plank, shingle, slate, or some other durable cladding, that would then tie into a cold roof assembly. This outer layers are called your "sacrificial layer," and it protects the inner wall systems matrix, no matter the configuration, cob or otherwise.

Regards,

j

Ok. But in the event of a pretty bad storm with a lot of wind, what sort of damage does it to do the cob (even lime plastered)? Does it eat away at it, or...? I just want to be prepared for what could happen and know how to repair my cob if needed.

Ok. But in the event of a pretty bad storm with a lot of wind, what sort of damage does it to do the cob (even lime plastered)? Does it eat away at it, or...? I just want to be prepared for what could happen and know how to repair my cob if needed.

If you are talking about a hurricane, tornado, or the like, yes there is going to be damage that you have to repair. This will come from flying objects for the most part. So what ever you are imagining, will probably take place, and have to be repaired accordingly. If you are asking about just general wind and rain storms, these will only have a normal accumulative effect on the sacrificial layer, pretty much like on any home. Over time there will be some degradation that will require a re-plaster, or fix applicable to the type of cladding/rendering the architecture received. How often will depend on exposure and biome. That is about as detailed as I think one could safely project without specifics on the structure, exposure level, and location.

If you are just fretting over the durability of cob, perhaps you should use a different construction medium, or stronger cladding method. Cob is not like a stone or plank of wood. If you through water on it, rendered or not with a sacrificial layer, and abrade it aggressively mechanically there will be degradation.

Jay C. White Cloud wrote:

Ok. But in the event of a pretty bad storm with a lot of wind, what sort of damage does it to do the cob (even lime plastered)? Does it eat away at it, or...? I just want to be prepared for what could happen and know how to repair my cob if needed.

If you are talking about a hurricane, tornado, or the like, yes there is going to be damage that you have to repair. This will come from flying objects for the most part. So what ever you are imagining, will probably take place, and have to be repaired accordingly. If you are asking about just general wind and rain storms, these will only have a normal accumulative effect on the sacrificial layer, pretty much like on any home. Over time there will be some degradation that will require a re-plaster, or fix applicable to the type of cladding/rendering the architecture received. How often will depend on exposure and biome. That is about as detailed as I think one could safely project without specifics on the structure, exposure level, and location.

If you are just fretting over the durability of cob, perhaps you should use a different construction medium, or stronger cladding method. Cob is not like a stone or plank of wood. If you through water on it, rendered or not with a sacrificial layer, and abrade it aggressively mechanically there will be degradation.

Hi Jay C. Any recommended waterproofing techniques for the cob itself? Many years ago (more than I care to remember) I worked as a plasterers mate. I seem to remember that with some of the gypsum plasters and cement renders you could include additives in the wet mix specifically to add additional weather/waterproofing. This was used most often when we were 'pebble-dashing' exterior walls. But I also remember additives being included in both bonding and browning mixes as well as thistle finish to deal with interior damp placement (bathrooms and kitchens).

I seem to remember one of the additives didn't seem much more than a wood glue - but I'm sure there was more to it than that.

thanks

Jeff

Wood glue is one of them. But you have to be very careful not to make it waterPROOF as it needs to stay breathable. If you don't, the layer right under it will collect water migrating through until the whole outer layer sluffs off. This is a problem with cheap stucco cookie-cutter suburban houses, the wood rotting from behind.

If you have continual sideways wind & rain (like a long cold rainy season), then you need something more to protect the cob, as Jay said. My friends stacked their firewood and tarped it to be the wind break from prevailing wind. I have also seen barnwood lean-to built on the side like in the old days, as a walk-in winter cooler that also protects the house siding.

R Scott wrote:Wood glue is one of them. But you have to be very careful not to make it waterPROOF as it needs to stay breathable. If you don't, the layer right under it will collect water migrating through until the whole outer layer sluffs off. This is a problem with cheap stucco cookie-cutter suburban houses, the wood rotting from behind.

If you have continual sideways wind & rain (like a long cold rainy season), then you need something more to protect the cob, as Jay said. My friends stacked their firewood and tarped it to be the wind break from prevailing wind. I have also seen barnwood lean-to built on the side like in the old days, as a walk-in winter cooler that also protects the house siding.

Ahhh - yep that makes sense. I'm guessing that the breathing requirement is also applicable to wattle and daub is that right?

Any recommended waterproofing techniques for the cob itself?

Hi Jeff, et al,

This could turn the conversation into something a little different but good information to have and related to the OP's original question. In a few words: DO NOT WATERPROOF UNDER ANY CIRCUMSTANCES!!!

You are correct, many that work in concrete (OPC) spend a great deal of time under some conditions, trying to waterproof the concrete. In certain applications (perhaps a pool?) this maybe germane, but for the rest, the most I would ever recommend is a water shedding treatment, that of course is still breathable. In general I recommend not using OPC of any kind, nor gypsum, and don't in my work unless specd by a PE for some strange reason.

Now for traditional Clay-Cob-Adobe-Bousillage-Bajareque-etc. Architecture and their renders and plasters, the only time you would ever consider applying a highly water resistant treatment would be if you are installing a traditional water feature or "wet" installation of some form. A bathroom would be a good example, and then I would use a "Tadelakt" style of plastering, with of course the proper mix formulas, and burnishing treatments.

Natural walls must stay as "breathable" (permeable) as the possibly can. You want to achieve a draft free interior, not an "air tight" one. That is why I have never even recommend the nasty habit of wrapping wood structures in things like "Tyvek."

As our friend R. Scott has point out, if you build you structure (no matter the type cob or otherwise) in a vulnerable and exposed location (e.g. side of the ocean, edge of a wind swept field, etc) then you are simply going to have to design for that climate feature. Stacking cord wood is a good example, as are additional rain screens, and heavier renders and plasters. I would most assuredly, if possible, in these cases with cob us a lime render and plaster, or at a minimum, a lime stabilized clay plaster.

Regards,

j

Thanks for the concise reply Jay C. For the lime plaster - I seem to remember reading a text a while back that mentioned something about this being the preferred finish coat during medieval times. Indeed most timber framed wattle and daub buildings were actually all white as opposed to the white/black structures that we see these days and associate with Tudor buildings.

Hi Jeff,

The "white and black" as it is called in Tudor work is a contemporary "disneyfication" of the vintage original work. Within my world of Historical Restoration this is very poor practice when done out of context, or scope to original work. Lime, if one could afford it, was the prefered treatment, though the majority, it would seem only received a rendering in earth based plasters. I would point out here, as a point of interest, that sucrose (sugar) and certain lipids (drying oils) had also been added to these mixes at times, and in very accurate and small measures to add in resistance to "freeze thaw" and/or to achieve a uniform patina.

Regards,

j