Building a Cob Oven

I've always wanted to build one of those dome shaped ovens from cob so here goes. 

 

The size

We decided to make the oven 800mm wide at the base (inside measurement) and some sited suggest that the height should be 3/4 of the base so we made this 600mm but suit yourself.  Just keep the proportions. 

 

The base

However you build the underlying structure, it must be strong.  A cob (pizza) oven is heavy.  The upper level of the base, the part that the fire is laid on, is made from fire bricks.  It is made a little larger than the inside diameter of the bottom of the oven. The rest of the base must be wider still to accommodate the thickness of the walls of the oven. We put down a layer of gravel with just cement powder on the structure before laying the fire brick.  This makes a layer of cement (without sand) that is full of voids for insulation.

 

 The core

The shape
We decided to use the catenary shape.  The catenary is not a round shape (semi-circle) or a parabola.  It is apparently the ideal shape so that the force from the weight of the shell is transferred tangentially down the shell to the base.
https://en.wikipedia.org/wiki/Catenary

It is formed easily with no mathematical knowledge by hanging a chain by it's two ends.  The chain droops down in this ideal shape.  

 

Stand a sheet of ply wood or similar, on its long edge.  Make sure that the upper edge is level.  Put two nails in the upper edge at the distance apart that you want the inside base of the oven to be (800mm in our oven).  Note that you are not going to cut the ply wood.  It is just for laying out the oven.

 

Hook one end of a chain on to one of the nails and adjust the link that you put over the second nail until the bottom of the loop is the distance from the upper edge that you want the inside height of the oven to be (600mm in our oven).   Take a can of spray paint and spray over the chain.  Take off the chain and you have the perfect catanery shape marked on the ply wood.

 

Measure the distance between the two nails and make a mark on the upper edge of the ply wood, exactly half way between the nails.  Drop a vertical from this mark down to the bottom of the curve formed by the spray paint.  You can simply use a builders square to draw a right angle from this mark down to the bottom of the curve.

 

Lay the ply wood down and make  marks on this verticle line every 10cm, starting from the edge where the nails are.  When you get to the apex of the curve draw an extra line half way between the last line and the apex (5cm spacing instead of 10)

Measure from each mark at right angles to the vertical line to the curve.  Wright these down.  You are now finished with the ply wood. Note that the first measurement is right at the base.  In other words from the vertical line you have just drawn, to one of the nails.

Get some material such as carpet underlay.  From this material, cut a series of disks with a radius of each of these measurements you have just made.  You should end up with somewhere around 10 disks of ever decreasing diameter.  Make one more disk at 5cm below the apex of the curve.  Make a small hole in the exact middle of each disk.  

 

Cut a round straight stick (dowel for instance) exactly the height you have decided for the inside of your oven. Make a mark on this stick every 10 cm and 5cm at the very top.

Get some sand.  Beach sand is great.  When damp, it must be able to more or less hold its shape.  The sort of sand you make sand castles with, with your grandchildren down on the beach.

Put the largest disk (800mm in diameter in our oven) on the fire brick and adjust the position so that it is centered.  Put the stick in the hole in the middle and pack sand around it.  Pack a layer of sand out to the outer edge of the disk so that it is level with the first mark.  Adjust the stick so that it is vertical.  Put on the next largest disk and continue this way until you reach the top.  You have now made the core that you will remove when you have totally coated it with cob.  We found it helpful to drape a piece of plastic net, such as is used to cover grape vines before harvest, over the core.  This gives a bit of purchase for the cob and reduces slump.  It burns away in the first fire.

Many cob ovens look like an igloo with the entrance sticking out from the front side.  You make it as a catenary as well but about half the height of the main part of the oven and of a width at the bottom that allows you to insert a tray that you plan to use into the oven.  It is a 'cylinder' rather than a dome and is covered with cob too.  A chimney is often inserted into this entrance just where it meets the dome.  Otherwise all the smoke comes out of the entrance.  A simple stove pipe, wrapped in chicken wire and coated with cob does nicely.

Making Cob

Cob is a mix of clay and sand.  It is rich in sand such that the grains are touching and so as the clay shrinks as it dries, the cob does not shrink.  We got our clay from  a nearby river and the sand likewise.  We did the mixing on the sort of  cover sheet which is used to cover floors while painting walls and did the mixing with bare feet.  The cob should be workable but as dry as possible.  You trample it and then lift the edges of the cover sheet to move the cob back into the middle.  Rinse and repeat.

 

Your cob will slump when it is first applied, so apply it to the outside of the core about as wide as the palm of you hand and about 10cm deep.  Allow a day or so between layers.  The cob will dry enough to support the next layer.

 

Much later, when you are using the oven, the heat of the oven will turn the inner layer of the cob into ceramic.  The outer layer will still be clay so rain will soften it and wash it away.  If you build the oven in a complete shelter this is fine but if it is outside you must add a layer of cement.  We first covered the oven with pink bats and a layer of chicken wire and then applied the cement.

Leave the oven alone for a week or two and then very carefully dig out the core.  Don't worry about the layer of vineyard netting.  Leave the oven for another few weeks.  It has to dry out a bit.

Build a very small fire in the oven and keep it going as long as you can.  This will dry out the cob.  Perhaps do it a few times.  At some point you can build a larger fire but not too big at first.  The vineyard net will burn out leaving its impression on the inside of the oven.  You will also be able to see a line where each disk was located.

Not a bad idea to paint the outside of the oven with a water soluble plastic paint or even lime it with a slurry of Calcium Hydroxide.

Potential for mRNA technology

 

 

 mRNA technology extends far beyond COVID-19 vaccines and is being developed for cancer immunotherapy, protein replacement, infectious disease prevention, and gene editing. [1]

 

 

Cancer Immunotherapy

Personalized Cancer Vaccines: Scientists analyze a patient's tumor to create custom mRNA sequences that instruct the immune system to recognize and attack specific tumor neoantigens (unique proteins on cancer cells). Late-stage clinical trials have shown strong results for melanoma (such as Moderna and Merck’s mRNA-4157 combined with Keytruda), as well as trials targeting lung, kidney, bladder, and pancreatic cancers. [1, 2, 3, 4]
 
 
Infectious Disease Prevention
Universal Influenza and RSV: Researchers are building fast-adapting multivalent mRNA vaccines for seasonal flu and respiratory syncytial virus (RSV) to bypass slow egg-based manufacturing. Other Viruses: Clinical and pre-clinical pipelines target complex pathogens such as HIV, Zika, Ebola, Nipah, cytomegalovirus (CMV), and malaria. [1, 2]
 
 
 
Protein Replacement & Genetic Disorders
Missing Protein Production: Synthetic mRNA can enter cells and instruct ribosomes to manufacture functional proteins that a patient's body fails to produce naturally. [1, 2]  Target Conditions: This approach is being explored for rare and chronic genetic conditions like cystic fibrosis, hemophilia, and muscular dystrophy. [1] Gene Silencing and Editing: mRNA can deliver gene-editing tools—such as CRISPR-Cas components or instructions to silence harmful liver genes (like KLKB1 for hereditary angioedema or transthyretin for ATTR amyloidosis). [1, 2, 3]
 
 
 
 
Autoimmune Diseases & Cardiovascular Care
Immune Tolerance: For autoimmune conditions like multiple sclerosis or rheumatoid arthritis, experimental mRNA is designed to calm an overactive immune response rather than trigger it.  
Cardiovascular Disease: Early-stage studies are testing mRNA therapies to reduce vascular inflammation, stabilize atherosclerotic plaques, or prompt heart muscle repair following a heart attack.
 
 
 
 
 

Vaccination

 This blog is word for word copy from an article in the 7March2026 copy of New Scientist on Page 20.  It details some surprising side benefits of vaccinations.  If it could be summarized in one sentence, it would seem that a vaccination causes a general gingering up of the whole immune system which, as you will read, has some beneficial effects.  The article is written by a New Scientist writer, Michael Le Page.

Heading

The surprising vaccine side effects that boost long-term health.  People often focus on the bad side effects of vaccines, but they can have some great ones too.

I am currently arranging to get a shingles Vaccination.  I had shingles at university and still bear the scars. so I really don't want to risk getting it again.  But I also have in mind the fact that the benefits of the shingles vaccine aren't limited to preventing shingles.  And this isn't unusual.  Many vaccines have benefits that go way beyond protecting against single virus of bacterium - fact that aren't nearly as widely know as they should be.

 

Let's start with shingles.  A study of more than a million people last year reported that those given the Zostavax shingles vaccine were 26% less likely to die from heart disease or experience a stroke, heart attack or heart failure during an average of 6 years after the shot - a massive reduction in the risk for such an easy intervention.

 

What's more, people given a newer shingles vaccine called Shingrix were 17% less likely to develop dementia in the next 6 years, compared with those given Zostavax.  Since, several studies have shown that Zostavax also reduces the risk of dementia, the overall reduction in risk with Shingrix should be even larger.

 

Flue vaccines also have cardiovascular benefits.  For instance, and analysis combining data from more than 9000 people involved in 6 trials found those vaccinated against flu had a 34% lower risk of a heat attack or stroke in the next year.  The benefit was even greater for people with a recent history of heart problems.

 

The new vaccines for respiratory syncytial virus or RSV, seem to help prevent heart problems too.  A study involving around 130,000 people over [age] 60 found that those who had one kind of RSV vaccine were less likely to be hospitalized with heart or lung issues than those who went unvaccinated.

 

Then there are the covid-19 mRNA vaccines.  They turn out to boost the immune response to tumors along with Immunotherapy, extending peoples lives

 

I could keep listing examples, but let's turn instead to why so many vaccines have these wider benefits.  We don't know the precise mechanism but it's not surprising that they do.

 

Viruses can do lasting physical damage to the body and the immune response to them can also harm tissues.  So-called cytokine storms, in which the body overreacts and releases too many immune stimulating signals, are often what kill people with infections such as flu or covid-19

 

Many viruses also target our immune system to help evade it, weakening our defenses.

 

There's this idea in some circles that natural immunity from getting a disease is better than vaccination.  It's bonkers for all the reasons above and more, and measles is a great example of why.

 

Measles vaccines have cut the number of deaths from the disease from more than 2 million a year before 1980 to fewer than 100,000 in 2024.  They have also had the unexpected effect of reducing the number of children dying from other infectious diseases.

 

Why?  Part of the answer is that measles kills off some immune cells, leaving children more vulnerable to a wide range of infections for years afterwards.  But measles vaccines also seem to train the immune system in a way that boosts its wider effectiveness.  This training effect is so beneficial, it's even been suggested we should keep giving children the measles vaccine even if measles is eliminated.

 

It would be too good to be true if all vaccines trained our immune system in this way.  There is evidence a few vaccines have the opposite effect.  But this doesn't mean they don't still save lives.

 

The key question is whether you are better off getting vaccinated than not.  All too often the focus is entirely on very rare or entirely imaginary adverse effects of vaccines instead of on the risks of infections or the wider benefits of the vaccine.

 

I have no doubts that will make me better off.  I'll be getting my shingles vaccine and a flu jab every year and the RSV vaccine when it's offered , at the very least.

23

To all Republicans, sane and not so sane.

This is a direct copy of an article on FB by Christina Lorey.  Good on you Christina.  I couldn't have said it better.  Criminals like Trump will arise in all societies.  The measure of a society is how you stop their actions and restore sanity to your society.  America has failed miserably in this and it is the responsibility of Representatives and Senators of the Republican party who have the majority in all four branches of government.  (Supreme Court, Presidency, House of Representives, Senate).  The rule of law is, and has been for many years, a joke in America.  Trump is just the latest and most extreme example and it has exposed that America is a failed society.

 

From Christina Lorey, on FB:

A message to all sane Republicans:

He pardoned 1,600 violent criminals.
You said nothing.

He bulldozed the East Wing.
You said nothing.

He interfered with the release of the Epstein files. You said nothing.

He took over the Kennedy Center and renamed it after himself. You said nothing.

He accepted a $400 million airplane as a personal gift. You said nothing.

He threatened Canada, Cuba, Denmark, Greenland, Venezuela, Colombia, and Brazil. You said nothing.

He tariffed just about everyone but Russia, causing inflation and instability worldwide. You said nothing.

He attacked a nation during mediated negotiations. You said nothing.

His ill-conceived war killed 175 children on day one. You said nothing.

He alienated and insulted our allies. You said nothing.

His ICE Army terrorized and murdered U.S. citizens. You said nothing.

He committed murder on the high seas. You said nothing.

He co-opted the Justice Department and directed it to prosecute his political enemies. You said nothing.

It’s time to start talking.

How to build a beaver deceiver

So why would you want to build a Beaver Deceiver.  Beavers build dams.  Dams make ponds.   This can result in the flooding of something you don't want flooded or can wash away of a piece of road if they dam up a culvert.  If you go the 'human way' and kill or remove the   beavers, you will have a life time job.   Do the job right and build a beaver deceiver and you have solved the problem  You can now benefit from all the myriad  benefits that beaver ponds create.

So how do you build a simple beaver deceiver when your only aim is to limit the level of  the water in a beaver pond (ie - not to protect a culvert).  You start by getting a piece of that black corrugated pipe of a suitable diameter (big enough to take care of the flow of the stream during the spring melt).  It must be long enough to go from the deepest part of the pond, usually found a couple of meters upstream of the dam and to extend a little beyond the dam.  To install it, you cut away a little material in the middle of the top of the beaver dam and lay the pipe in this notch.  Pound a couple of wooden stakes into the top of the dam, one on either side of the pipe and connect them with a board or similar which rests on top of the pipe.  This board will hold the pipe down while the beavers  repair the damage that night that you have done.

Now as shown in the diagram above, you must build some sort of a cage for the inflow end of the pipe.  It should have a mesh lid on it an set so that the top of the cage is below the water level.  In fact it is best if it is below the level that ice or any other floating object will reach.  The wire mesh that is used to reinforce concrete slabs is a good choice and myself, I prefer a round design rather than the rectangular one shown.  Cut off the cross (horizontal) bars from the bottom of the mesh so that the cage can be pounded into the bottom of the pond.

So how about protecting a culvert.  Proceed as above but make sure that the pipe is long enough to extend into the culvert.  Construct a cage over the rest of the culvert.  One more thing and you are finished.  You are in danger of siphoning down the pond and you don't want that.  Beaver pond complexes are a great tourist attraction besides all the good that they do.  Take a hole saw on a battery drill and make a few holes on the top of the pipe where the pipe leaves the dam plus a couple more.  This will break the siphon.