Re-plastering necessary for cob/Adobe if it is not exposed to the elements?

I have heard that there is more or less annual maintenance required for cob and Adobe; specifically they need to be replastered every year.

Is this true no matter what--like if I build a cob structure that is entirely inside the envelope of my house? Or is it only based on the idea that the outside elements, or differentials between outside and inside conditions, degrade the plaster of cob/Adobe exterior walls (both on their exterior and interior surfaces) thus requiring the constant repair?

Hi Ned,
I haven’t heard of that strict maintenance routine. If exposed to rain cob and adobe might need regular re plastering. Otherwise I can’t imagine why that would be necessary. And of course it would be much wiser to protect the cob from rain than to be constantly repairing the damage.
I live close to a 700 year old castle ruin made of rammed earth. I don’t think anyone re plastered  it since 1492. And the wall and tower still stand.

Maybe the annual maintenance is wise if unprotected walls are lashed by rains.  What is more wise: always follow the "good hat and boots" mantra

In areas where earth walls are exposed to the elements, such as Africa, etc annual maintenance is done to keep the structure in good condition.
They are usualy built entire of mud, maybe with some timber of leaf protection on the roof, so are 100% exposed.
Westerners ususaly have greater wealth and build roofs, wall protection with verandas etc and then that maintenance is not required.
Benjamin, where is that castle you mention?

This is good info everyone, thanks. I have a vision of building either a Russian fireplace, rmh, pizza oven, or some hybrid of these out of cob or Adobe, in a central location within my house, and was wondering whether it would require regular replastering. Sounds like it wouldn’t, which is great.

The Russian heater would used fired clay bricks as the central core.

My house has cob walls under about 2 foot eaves, with a lime render. The lime render helps a lot and I do not need annual maintenance. A fresh coat of whitewash occasionally is fine. We get about 1.8m of driving rain per year hitting the walls. I have another "temporary" cob building next to the house which I built about 8 or 9 years ago and left unrendered. This has pretty much no eaves. It's weathered significantly but I've deliberately left it to see how it's coped. It's held up surprisingly well all things considered, but in these conditions if it was my main house then I'd want to be doing annual maintenance on bare cob. I think a good lime render is the solution though - look at the centuries-old cob cottages in England still going strong.

Thanks Jon
Your experienced anecdote is of rare quality, it seems NZ has bouts of extreme weather.  A good test for construction techniques, I think

I know the geologic and volcanic complexities there are unique,   I read, and someday hope to see some, especially that South Island.