[Re: Cob: Couple Of Questions]

[Sarna Salzman]

When bonding clay for ceramics and pottery, I use a vinegar-slip to help
connect two pieces of drying clay together. I'm not really clear on the
chemistry of it, but it is supposed to be more effective than a water-based
slip. Wouldn't the same apply to cob? (Though, I guess that might involve a
LOT of vinegar!)
Sarna


> 
> If the wall dries before you get back to it for the next layer, the bond
> between the old and new layers will be significantly weaker because you
> will not be able to get as good a mechanical bond since the layers will
> not be intermixed.  To improve the quality of the bonding, whenever you
> are done for the day, it is best to put a lot of holes in the top using
> your thumbs or a stick of similar diameter.  By doing this, you provide a
> means for interlocking new cob with the old cob even if it dries.  It
> won't be as good as if the wall were built continuously, but for most
> cases should be more than adequate.  If the wall has dried before you go
> to put on the next layer, it is important to thoroughly wet the surface
> where you will be adding new cob (preferably repeated soakings over at
> least an hour or two), this won't soften the old cob to any significant
> extent (unless it is a really poor quality high clay mix), but it will
> significantly improve the bond and reduce problems with cracking along the
> joint between the old and new layers.
>