The House of Many Unfinished Projects is where I live.
Being an Architect & a Natural Builder, the creative side of me is always having new ideas; starting a new project, or experimenting with something new. Often times, it’s not long before my next ‘great idea!’ comes along and there I go….leaving behind the unfinished work for another day.
Never trust an Architect with a ‘finished’ home! I believe the first thing we learned in architecture school was that ‘you are never finished…..never…..ever…..finished’
Lo & behold, this blog post is about actually FINISHING (and I use this word loosely) my Earthen Oven. I started the process of building it a little over a year ago; we’ve been getting lots of use out of it over the past year, and I’ve slowly done a little more here and there when there’s time. Through the use of using it, some cracks have appeared (this is normal) and the base was never really finished. The roof came into the picture late, so there was some rain damage here and there.
In this blog post, I will explain the steps I used to complete the base of the oven with a cob mixture, how I repaired some cracks, and then the final plaster coat I used over the entire oven and base. You may find this info to be helpful whether or not your oven needs some repair work, or maybe you are just wondering how to go about making a final plaster coat. Either way, I hope this helps!
Cob Work Around the Oven Base
I decided to make a 3-4″ base right at ground level out of Portland Cement; I was worried about rain water collecting and reaching the earthen plaster; you can see the concrete base in the picture; this should help divert water away from the oven. The base of my oven was made with salvaged cinder blocks; you can see in the picture how the funky angle created a pretty rough surface; I decided to make a cob mix to level out the base and create a smooth curve. I decided to go with a HEAVY straw cob mix. I know that when straw is added to cob, the result is SUPER DUPER STRONG cob. Being that the oven base is vulnerable to kicking and other abuse, I wanted to go strong. I also wanted to be able to stretch my clay mix farther; straw helps with this.
The basic recipe is this:
– 1 part clay (not screened)
– 2 part sand
– as much straw as I could mix in (lots)
Be sure to wet the existing surface prior to applying the cob; it will bind better.
Fill in all voids with the cob mix; do any sculpting or shaping with this mix.
Trowel the cob as to compress the material, push any loose straw ends into the mix, and smooth the overall surface.
Trim any crazy straw ends sticking out.
Filling Oven Cracks
Use the same mix as above; the straw is not necessary, but if you have it, use it.
Use a sponge to fully saturate the oven crack with water.
Take a stick or a nail and rough up the existing surface a bit.
Stuff your cob mix into the crack and patch.
Compress mixture into the crack with your hand or a trowel.
Let dry.
Final Earthen Plaster Coat
Start with soaking your clay in some water for a day or two. Mix with a paddle mixer if you have one.
Mix 1 part clay: 2 part sand (This ratio depends on your clay source; always make samples when doing plaster work; try a few different ratios and let dry; see what cracks and what doesn’t….what’s strong and what’s weak?) Once fully soaked; screen through 1/4″ hardware cloth (or smaller for a finer finish) to remove large rocks, etc. Apply plaster mix with your
hands; I went about 1/2″-3/4″ thick. Mist oven surface prior to applying plaster; scratch existing surface to create a good bond. Once plaster is ‘leather hard’ trowel finish or use a plastic lid (yogurt lids work
great); this will compress the plaster and make it very hard when dry. This also will smooth out any bumps, cracks, etc.
Continue to trowel the surface multiple times through the drying period; if you stay on top of it as it dries, you can typically buff out any cracks that form.
For a more protective finish; try painting on a lime wash or finishing with a linseed oil or glue coat once the plaster is dry.
This was helpful in me building my oven. I am doing 2 3″ layers over a sand mold. The first layer I am not using straw (per the vid I am going by that says it will burn away). Upon finishing my 1st layer, I had several cracks all around and 1 that seemed pretty significant. (I could stick the tip of my finger in it)And although I covered it with a tarp (old) it still got wet and I see the damage that you speak of, which wasn’t to bad(some sand trails) but it still held together well. I have patched the cracks and waiting for them to dry. The patching seemed to go well. Thanks for your blog, it has been the best one I’ve found so far. I am using my oven in our Living Nativity to show how bread was cooked for centuries, even in Israel at the time of Jesus’ birth. Do you have any tips on moving an oven to a different location? Thanks; Mark.
thanks so much mark! as far as moving an oven, i do not have personal experience, but i do know that it has been done! i think a flat bed trailer, or similar, with really good shocks will be your best bet. just build it right on the trailer