cob blog, please have a look and give any advice!!

We are building a cob home in Zimbabwe, we are not experts so any help and advice would be appreciated. Please follow us on http://dancelikeanelephant.blogspot.com/

Thanks!

Zim,

The foundation looks nice. I can't wait to see your design. Adding the lime was a good precaution.

What is the rainfall totals for monsoon season? How are you going to protect the walls? Elongated eves or coating mixtures? I will be interested to see your project come together and wish you great results!

Hi Greg,

Thanks for your comments and questions. The rainfall in Hwange is 600 mm between November and April. The thatched round roof will overhang to give the walls some protection from rain. The stone foundation will come up above ground level to give some protection. I also want to do a lime plaster for the walls.

The main problem in this area is termites. I am looking at how to make my own termite barrier from sheet metal. There are no manufactured solutions for this in Zimbabwe. Also to protect wood I am looking at treating wood with Borax. Any ideas on how to stop termites?

copper foil?

Termites can't live in dry places and will not eat dry wood. Whatever you do keep your timber as dry as possible. Don't encase it in cob but leave some exposed (exposed to the inside of the house might be preferred) to allow a way for it to dry out quickly and breath.

They will burrow in tubes through anything they can in order to get at moist wood or they will surround dry wood and eventually it will moisten from the activity of the hive. I suppose a metal barrier will work, but just as well is rock or concrete. Perhaps use a concrete based mortar on your footing even if it's just a few inches of concrete/rock. If they can't physically burrow to the wood they won't be able to eat it and this mortar can be mixed with sand and clay. Your goal is a super-hard, rock-like layer they can't eat through. Unlike metal concrete won't rust away if exposed to a little moisture.

Chemical agents are a short-term solution. Look at railroad ties for example. They're literally soaked in heavy tar and chemicals yet when they stay moist they will rot or get eaten by termites pretty quickly. The other thing about chemicals is that they leach out eventually. I'm not saying not to use them, but I am saying that you should make keeping the timber dry and unreachable by termites the top priority. Chemicals will only help, they won't solve the problem in any amount.

Inspections would include looking at the bases of your footing for tubes coming from the ground. Destroy these on sight and chemically treat the area with whatever will KILL termites. http://www.hadleypestcontrol.com/assets/images/Termite_Tubes.jpg 0
Tubes likely mean they're eating your house not living in it. If you kill off the tubes usually that stops the problem, but they're persistent and will continue to try to find a way in. If you kill enough scouts with chemicals they will stop trying to come back after some time. Though it's not environmentally nice I've heard poring mineral spirits into their hole will do the trick. It destroys the chemical scent trail they leave marking your house as good eating and it kills a fair number of them at the same time. I only say that because I imagine you may not have good access to enviro-friendly alternatives out there.

Make sure the floors inside are sealed as well. If you want cheap flooring earthen tile would be do-able. Simply mix up clay/sand/concrete and tile the interior to prevent them from tubing inside. There are other options but the basic principle is to make something they can't physically tunnel through. Linseed oil is a typical way to finish these kinds of traditional floors.

Another thing to look out for is roaming colonies. You want to keep an eye out for colonies starting under the eaves of your roof. I would treat these yearly at the beginning of drone season, when you see termite drones flying around. That's your best hope of protection. Sodium borate, borax, salt and lime are all somewhat effective at deterring, but not killing, termites, but they do kill fungi, and kill plants and algae... Mixing all or some of those together (whatever is available) would make a decent preventative treatment under eaves and on exposed wood surfaces.

Do you worry that Mugabe might target you next so that all of your work may be in vain?

Thank you for the information on termites. Another problem seems to be wood borers. I was hoping to treat wood only with borax but think this maybe won't deter wood borers?

To answer the last question. There is very little stability living here in zim, there is no ownership of land anymore, but the plot of land where we are building has been given to us by the chief and is very small, it is the same size as any rural family here is given. Land issues have been mainly with commercial farms. So we hope all will go well, but even if it doesn't we tried and we will have the experience of building our own natural home!

Zim,

It seems Sodium Borate is the best non chemical way to combat Termites. It is available commercially under the name Timbor and Bora-Care. I don't know how the availability might be in your region; but both the products are Borate Salts. Boric Acid may be more available to you and could be used to coat or treat your wood, either by soaking or painting exposed access points in the lumber. Neem oil is a more organic solution, but don't know where one would find large amounts for construction purposes.

That being said, what wood surface are you concerned with in a Cob Structure? My understanding of termite infestations is that they occur at the intrusion point of wood in contact with the ground (or easily accessed from the ground), as termites are subterranean. With Cob you have a stone sub foundation that merges with the cob wall which contains no food source. Other than door frames that might be accessed from the ground, nothing gives them egress into the wooden parts of the structure. Incidentally, aluminum flashing for roofing can be used to wrap the footing of any wood used for door/window framing that might be a concern.

I can't say for certain but I believe that once dried, cob as a material is too compact and hard for termites to burrow or travel through. The lime in your foundation and exterior finish should be a barrier as well. So they should not be able to infest the wood in the rest of the structure.

i dunno, here in AZ, we have subterrean termites, and they will chew thru high percentage agg concrete to get to wood.

Am tempted to tell you do douse ground well with boric, then mix some in with the concrete you pour as a footer.

would also be tempted to use a flashing or foil layer somewhere to keep diggers out too.

No windows next to or in the door, and best to keep lights away from door too, to keep the insect attractors away from easy entrances.
Plant marigolds and mint or lemon grass around perimeter, to keep even more critters away.

Termites can't chew through carefully laid concrete. They can find a small hole or crevasse to burrow through and they can chew through many soft plastics. They will also burrow around a barrier by building a mud tube. As Greg suggests flashing would probably be most useful around and under doors and door-frames and wood that's close to the foundation. Copper would be expensive but I guess it would last longer, there may be a better alternative available to you like aluminium or something.

http://www.aces.edu/pubs/docs/A/ANR-1035/

Wood borers are another case entirely. I'd say consult an entomologist but I doubt you'd have easy access to that. Wood boring beetles come in varieties, some eat deadwood, some don't. Most need humidity, a few don't. Some will avoid common chemicals others don't mind them.

If you have some way of freezing them that can be an effective treatment, but it's tricky to pull off. Obviously, prevention is your best ally.
I think if you keep it dry that would go a long way. If you have access to pressure treated lumber use that in the main structure of the home. Borax, also known as sodium borate, will help as you suggested, if you drench your lumber in it before you use it. Between the two and common sense inspection I think you'll be ok.

Last note on wood borers is that there are some species that will live with the wood for a long time before hatching and eating it. Be careful, then, about wood selection. Make sure to pull the bark off as many of those lay eggs on the bark or tunnel in from the outside so you should be able to see if a particular piece of timber is already infested.

Thank you for all the information and advice, I have decided to not have any wood directly in the ground, to lower the risk of termites, there will be poles in the roof structure and wood for the doors and windows only. The house will be 10 m diameter round house, with a thatched roof, so think a central support structure is needed, but would prefer to use something other than wood.

On my last post on the blog someone has commented on ancient impregnation techniques http://dancelikeanelephant.blogspot.com, soaking wood in mud for a few weeks and putting it in a mud drier, there is no more detailed information, does anybody know anything about this? Not sure how this would last through time, maybe for wood for the roof structure that stays dry it could work, but exposed to the elements I wouldn't have thought this would work.

I am trying to make sure that the building has the least possible environmental impact, I don't really want to use any cement, I have used a minimum percentage of lime for the mortar in the stone foundation and would like to leave it at that. I also don't want to use any harmful chemicals so the most natural preventative measures to protect the house from insects is what I am looking for. I have managed to find a supplier of Borax here, and bought a 20 kg bag, the crystals are very big and don't dissolve well in water so maybe I need to crush them further first.

Cool blog laurie!

I have used borax recently, and do not forget to oil it afterward,
as it does not go that much into the wood, and it would be washed away.
Oil makes it stick.

Mine was thin. Would it be possible that it melts in something else than water?

Hi Nicholas, thanks for that info, what oil did you use to seal it? linseed oil is not available here so really need an alternative!

Zim Lion wrote:Hi Nicholas, thanks for that info, what oil did you use to seal it? linseed oil is not available here so really need an alternative!

Xisca better...
The basis was linseed oil, it is a ready made mix, some citrus oil in it too. I live in a place with a lot of german people, so it is imported.
I guess you will have to rely on some internet purchases for a few things...
And also see what is locally used. We cannot know what oil source you have in southern Africa.

Wonderful blog, wonderful building site!

keep up the good work. *Almost* makes me jealous and want to build more. My wife and I have just spent a year in our cob house after taking 5 years to build it ourselves... it was hard work and I'm glad it's over, and we didn't even have to worry about elephants!

if you'd like to see our blog, which is very similar to yours, only further along and in the woods of California, check out www.ideamountain.com

If you have any questions about any aspect of the building as it goes on, feel free to email anytime to tys "at" ideamountain.com . We're not experts, but have a bit of experience.

good luck and take it one day at a time!
Tys

Tys, Thanks for your encouraging comment! and thank you for sharing your amazing blog, it's great to hear from someone who had a vision and has seen it through, I'm still on the making it happen part of the dream!! and yes I will let you know if I have any questions as the building progresses!!

All the best in your future projects!!