Erin Cannings

Hi,

I am just wondering what your batch mixture is and what will your final plaster coat be?

I have been soaking some hydrated lime for 6 weeks, i have some sand, i have lots of clay.. what should the recipe for a reliable plaster coat be- considering i already have a plaster coat containing the clay, sand, straw and wheat paste (which is cracking more now)

I know that cob ovens crack and eventually might need rebuilding. I would like a plaster coat that is more aesthetic then the cracking up earthen plaster I have now.

many thanks

Hi,

i built my cob oven 6 weeks ago and we have had a few firings and pizza nights and it works well- i love cob ovens- simple and rewarding in so many ways. My question is relating to the protective plaster coating. Can you put a lime plaster on top of an earthen plaster?

My insulation layer was clay slip and sawdust as suggested in kiko denzers book. Initially it seemed to flake when it was drying and i didn't want it to just blow off and fall apart so i applied an earthen plaster which was made from clay soil, sand and wheat paste and chopped up straw. I didn't want to wait til then oven dried out completely before i plastered because i had the anxiety of losing my insulating layer to the elements.
The plaster itself has held up well to firings and only hairline cracks are appearing in the plaster which is less then 1 inch thick. I would like a more protective coating which i feel a lime plaster would offer. I am not sure if i can combine the two types of plaster so i would love to hear anyones thoughts on what i can do to make a more waterproof coating. I do have a small roof over the oven but sometimes the rain blows in sideways and it gets exposed.

many thanks for your time and replies.

it was probably the lack of fatness of the subfloor slab that made it crack a bit- its probably only 2 inches thick- thanks for that information.

Hi,
will the sub hearth floor be fine as it is? bricks will go right on top. should i amend the floor with fibre- but that would mean pulling it off and reprocessing.. My concern is the thermal layer of the dome and what i can do to prevent cracking there- i don't see people adding fibre to that layer?

HI,

I am attempting to build a cob oven solo and i have never cobbed before.. I am using soil from the bottom of my now defunct dam and hoping it is ok. the ratio i am going with is 1 soil to 3 sand because to me the soil test looks more clayish...but i basically am guessing and would love anyones input who has some more experience then i do..
I am at the point where i have just made a subfloor pad out of the 1:3 cob mix and as it it drying i can see some cracking... so do i add more sand and worry about the sand being too much and the oven slaking/falling apart.. or just go with the mix. I made some test bricks but i may have over tested them because basically in the end all of them smashed apart (maybe i dropped them 10 times...is that too much?) is cob gonna break eventually?

Because i am doing it solo and just going from cob oven blog to blog and i have kiko's book, i am anxious about stability long term...
thanks for your help!!!
oh and the soil test has been sitting undisturbed for about 1.5weeks.