[Cob] RE: Adhesion/bonding of PVC and Cob

[littlehouseantiques at att.net]

Not a scientist by any stretch of the imagination but seriously doubt that COB and PVC form a bond 
of any kind (molecular or otherwise!)  

I, like David, believe that the reason that PVC wouldn't come out is because a vacuum was created
between it and the cob.  

Reason I think this is that I have many times used 4 inch PVC pipe as a "form" when making pots and
planters with hypertufa and believe me it is the VERY dickens to "break" the vacuum that is created
between the surface of tufa and PVC...just when you think nothing short of dynamite is gonna get that PVC
to move, you will hear a little "wooshing" sound of the air rushing in there and then and ONLY then can
you pull the PVC out of the hypertufa (and even after the vacuum seal has been breached it is still very
tough to remove!)    The smoothness of the PVC should make it an excellent material to use as a form because other materials will not "stick" to it (tufa, clay, cob, etc.) however, I think it is the rigidity of the PVC that causes the vacuum and the removal difficulties.  

Kathy in PA

  

-------------- Original message from "David Knowlton" : -------------- 

> sounds like a garden variety scientist is needed to study this. 
> 
> conventional wisdom says clay will bond better with rough objects. 
> is this something like water tension, or suction? you know, the steamy 
> hot saucepan lid that gets 'stuck' to the smooth counter? 
> 
> any materials scientists out there? 
> 
> dave in tampa 
> 
> >From: "Marlin" 
> >To: ap615 at hotmail.com,coblist at deatech.com 
> >Subject: RE: RE: RE: [Cob] sinking logs in cob? 
> >Date: Fri, 01 Oct 2004 14:24:50 -0400 
> > 
> > ...snip..... 
> > 
> >An anecdotal story...... I put a cutoff piece of PVC water pipe in a Cob 
> >model as a form that was to be pulled out later (I've used PVC sleeves in 
> >cob before for water/elec. thru's the wall), it was supposed to be just a 
> >form for the model's arch. I couldn't get the PVC (how slick is that?) out 
> >of the wall after it dried and couldn't tap it out with a chisel and 
> >hammer. I didn't want to start making big blows on the little 2 inch thick 
> >cob wall but it impressed me that the PVC was probably gripped in by the 
> >cob at a very microscopic level. 
> > 
> >Marlin