Waterproofing Cob Bench

Hi all, i happened to leave my cob test bricks in the rain and to my surprise they are not waterproof at all. This is even after i had left them in the fireplace and the next day were hard to the touch, like they had been fired..obviously i was mistaken.

Sooo, my question is once I build the cob thermal mass, will it be waterproof once dry or do i need to waterproof it with plaster?

it will not be waterproof without some sort of render.

Karl Meisenbach : It would be a very good idea to treat your finish coating to some type of a 'waterproof coating'! The ability of both Cob And Adobe to breath is a great plus
in its use in Houses, but some protection to the top of the built-in furniture where spills are possible is valid! There is a little natural loss of grains of sand and fine powdery Clay
due to wear through friction on a daily basis until the top of the cob bench is sealed anyway, so while it is something that can be put off on a daily basis The final seal coat will
be something that gets taken care off naturally !

So, unless your structure is on a flood plain, living with the natural ability of the cob to breath will not be an issue, possible staining, or a desire for a more Formal looking
finished Cob bench, and the fine dust and sand will take care of of The degree of additional protection that you might need for an event like a major spill that occurred, soak
-ing a 'futon mattress'-like covering left on your Cob bench for hours be for it was detected !

Their are major types of housing construction accommodations regularly used for outside Cob and Adobe walls, like extensive roof overhangs at the eaves, stemwalls to protect
the lower parts from excessive contact with rain water and splashing water from off of the roof line, as well as waterproofing finish coats to the exterior walls, but the longevity
of all these systems should put your mind at ease !

For the Good of the Craft ! Think like Fire, flo like a Gas, Don't be the Marshmallow ! As always, your comments and questions are solicited and Welcome ! Big AL

Karl, for inside aplication, i'd say do a finish with wax. But only on top. Let the sides breathe with a lime render for example. And lime render plus wax on top. Otherwise, on the outside, i'd say big stones and concrete on the top. Concrete made out of portland and NHL5 hydraulic lime or clincker. Get the stones to overhang to protect the sides. And give it the same treatement on the bottom 4" of the bench. Or make a concrete bench altogether.

Karl M.: In the Cob Forum Dale H. is going through a repair cycle on outdoor cob benches, this will give you a better idea on life of good untreated cob structures and proper care !

Dales cob bench restoration project - - - - This should clear up things a little ! Big Al !

Allen and Satamax..Thank you for your help on this!

I just want to make sure that my cob bench, once dry stays dry.

Allen, you mentioned that sealing will occur naturally..then why didnt my bricks "seal" even after being in the fireplace with a roaring fire for half a day hours?

Could it be that my clay is really silt or something else that ive overlooked thats causing this?

Karl M : I'm sorry for not being clearer, Cob breathes naturally, If you were trying to burn wet wood the cob would make an accommodation and transpire the excess
moisture from within the horizontal ductwork out thru the Cob bench- just like a living green plant leaf will transpire excess water as vapor from within the plant leaf to the
atmosphere !

In cases of extreme moisture the Cob will absorb lots of moisture from the air into the Cob ! This can be a problem in the extreme high vapor pressure of a Green House, But
not within a typical house/home ! The history of Cob and Adobe use stretching back thousands of years should comfort your fears, It has a proven track record !

With lifes experience I am slowly growing Anti- Concrete, being willing to recycle old concrete where ever possible, just not in favor of the many trade-offs in new concrete !
that having been said, There are many good ways to seal and waterproof the final or Dress Coat of Any Cob or Adobe surface !

The temperature to 'Fire' Cob or Adobe bricks is considerably higher that you can reach 'Baking' them in a fireplace and even then will only slow the gradual slumping and
eventual collapse and re-absorbtion into the Earth of all Soil- Ashes to ash ! Dust to dust ! yahdah! yadah ! Big Al !

Allen, don't grow anti concrete, the romans made fantastic use of it. May be the egyptians too

Tho, i'm not too keen on concreeting all and everything. I mean, over here in France, as well as in italy, we're the kings of the world to build into shuttered concrete. Nowadays, many houses are made this way. And they might last not only hundreads of years, but thousands. And i can see this becoming a problem in the future. As well as tarmac'ed roads. Around the big cities in france, they do suburban houses, one plot of land, about 100'x100', a tarmac road goind to it, same for the alley going to the garage, a concrete house, and all this for lenghs around cities. Where the soil was the best. If one day we run out of petrol. The situation will become very complicated around thoses areas, to recover the ground. And usualy, the houses aren't built around swampy or hilly areas, they're on the best soil, which has been worked by generations of farmers.

But in turn, making shutered concrete houses in tornado alley would seem the most clever idea of all time to me. This would save lives, and last. Even more, if they didn't make pitched rooves, but flat concrete ones. Nothing would fly anymore with the tornadoes.

In France, we have a similar prob with a few known areas where they get flooded every ten years. I always say, get the bla..y houses on stilts!

Huh, sorry for the rant.