Limewash as insecticide on old cob before applying new cob

Hi everyone! I'm finally starting work on the old cabin I posted about awhile back. It was built with small timbers held together with cob. The builders had intended to continue with the cob so the walls were 18" thick, but the project was never completed. The cabin has been abandoned for the last 5-6 years and I am going to try to finish what they started now.

You can see where bugs have burrowed into the cob and the wood over the years. I am about to start applying new cob over the existing structure, but I feel that I should do something to get rid of any bugs that may be living in the wall currently before I move forward with the project. Can I spray or mop the surface of the existing cob/timbers with a limewash as an insecticide and then cover that with the new cob? Or should I be looking at a different solution for this situation?

Any other tips for preparing the surface for the new cob would be appreciated as well.

Thanks!

Hi Jane,

I have a pest control and biology background, and can tell you that what you are seeing is probably old activity. I could tell you more about the "wee beasties" if you could get a sample of one of them. A product like "Bora-Care" or other borate based mixes would be your best bet if you still feel a need to do something. Diatomaceous earth is also very effective, but would be rendered mostly ineffective if you plastered it, it's meant to be used in dry powder form. Let me know if I can explain more.

Regards,

jay

Is the area you are wishing to lime-wash below the wooden lathe? Lime, although still breathable, will slow the passage of water through your wall, so if you are thinking of laying a layer of lime in between layers of cob, I would advise against it. If too much humidity is built up inside, it could condense fairly quickly in the center of your wall when it comes in contact with the lime... this effect probably wouldn't be too bad with just one or two coats of limewash, but something to consider . I agree with Jay, and believe there is no need to cover up old tunnels from insect invasion. I would wet the surface and scratch the old cob deeply, possibly even knocking some segments of the wall out every so often where fresh cob could adhere to the old stuff better. I would also use a clay slip painted on to the old lathe and the old cob moments before applying fresh cob. If this wall was done with waddle and daub sytle cob, as it appears from the photo, it will be more difficult for the wall to act as a solid mass if it is layered like a sandwich rather than homogenized into one mass. Scratch it, indent it, wet it, slip it would be my advice to give as much tooth on the old cob for the fresh cob to stick and dry without peeling off and leaving a weak section between 2 layers.

Jay, you are probably right that it's old activity as I didn't see many actual bugs at all. There are just dust trails where you can see something burrowed into the wood and some holes in the cob as well.

Jim, thanks for the tips on apply the new cob! I have been reading about using a slip and also wheat paste along with much of what you mentioned. The plan is to apply 3-4" of cob to the inside and 8-10" to the outside. The inside will be done first, then I can get moved there and start working on the outside. I realize I may not finish the outside before the weather prevents me from continuing or at least seriously slows down my progress. Winters here can range from very mild to rather severe, so I will just have to play it by ear as I go.

I guess I will not worry about the bugs and just get on with the cob!

Thanks to you both very much!

Hi Jane,

You maybe surprised to know that most of what you see in wood as far as holes and frass (that is the dust you referenced) is not from going in, but "morphed" grubs coming out as beetles. Beetles (Coleoptera) are the number one infestors of wood past termites and ants. The females lay their eggs when they smell it as being truly in the conditions they need depending on species. There are many theories behind this from fermentation to fungal activity being the trigger to lay eggs. Many species also need the wood to have a higher moisture content than what you would find in an older structure like you have shown in the photo, (but not all, like death watch beetle)

Good luck, and let us all know how it goes.

Regards,

jay

Jane Porter : From your earlier comments, and what you have said now, I would divide up your house into 10ths, inside walls 4, outside walls 4, Roof 1,
and cracks and windows and doors 1 !

Go around inside and out and find the areas that need the most work done to make tight, then sit down with a plan. There maybe areas where 1 Cob coat
outside now will tighten your walls easier and to better results than the same time and materials inside!

With a plan, attempt to work on the outside areas while the weather is working with you, latter you will pick up a little speed from the heat in your cabin!
Don't forget that your roof and your top half of your walls is where you lose the heat energy that slips out through all the little cracks and promote the
cold air drafts that cool your floor,

Finally anything that you can stack around your perimeter boxes, hanging sheets, while it may make your cabin smaller will slightly retard the infiltrations
and make them seem a little less cold, it is possible to use card boat especially right around your sleeping area to make a draft free zone !

Every trip into town, especially those ' I've got to go get this One item'- trips should have you backpacking in some form of insulation, and cardboard can
be recycled for a mulch? weed killer ! It should always be burned before the furniture, or so say the notes left behind by the Donner party! Big AL

I have always under stood that the wheat past flour was for finish coats, I was thinking structural cob with cat tail fluff as an amendment or any good short
length straw substitute ! Lets hear see what Jay White Cloud can share with us !

Allen that was some great advice...I don't think within those parameters there are many details to add other than subjective ones not worth mentioning.

I was thinking more radical thoughts after seeing photos. like adding a new wall and floor system inside (you will lose space) to give you a cleaner demarcation in the walls and more volume for insulation of your choice. If you used a wall truss system you would lose more space but gane storage and shelving depending on the thickness and insulation type. Other than that Allens guidance sounds pretty darn good at this time.