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

[David Knowlton]

well if it's consistent, might it make a good roof tie down point, etc?

david

>From: littlehouseantiques at att.net
>To: "David Knowlton" <pilot1ab80 at hotmail.com>
>CC: lightearth at onebox.com, ap615 at hotmail.com, coblist at deatech.com, Subject: 
>RE: Adhesion/bonding of PVC and Cob
>Date: Sat, 02 Oct 2004 08:41:08 +0000
>
>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

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