Papercreters: [papercreters] Re: Papercrete Roof

Monday, July 26, 2010

[papercreters] Re: Papercrete Roof

Speaking of buildings in general rather than papercrete specifically...

In a damp climate its necessary to use a vapour barrier on the interior side of walls, otherwise as damp interior air cools on its way outward it condenses, and water builds up.

On occasion people add a vb on the outside to damp walls in the mistaken belief it'll stop rain soaking in. It may do, but it also prevents evaporation, resulting in greater dampness in the wall.

Warm interior air holds much more water vapour than even wet outdoor air in winter, hence the dew point is reached when it cools. The vapour flow in housing walls is from interior out, not the other way. (If it were the other way, houses would flood.)

Another damp problem happens when a wall has insufficient insulation to prevent condensation occurring on the interior surface. Only a very small amount of insulation is needed to stop this though, at least here down to -20C, so I doubt that would be an issue with papercrete, unless you're building somewhere extremely cold.

--- In papercreters@yahoogroups.com, "ndgogiraf" <ndgogiraf@...> wrote:
>
> I think it depends on the outside temperature, inside humidity and insulation of the roof. Does it get really cold there?
>
> If it is very cold outside and cold enough on the inside layer of the roof vapor barrier such that the humidity inside will condense on that barrier,
> AND
> there is not enough papercrete to insulate the inside air humidity from this vapore barier so that the temperature differenc of the moist air when it finally reaches the barrier through the papercrete is ... something about the dew point.
>
> Basicly, if you have enough insulation (papercrete or whatever) between the inside of the room and the outside vapour barrier, so that by the time the moist air reaches the vapore barrier through the papercrete , as it moves through it changes it's ability to hold water so it will change it's tendency to condense on colder surfaces, and you will be fine. However if the insulation between the inside warm humid air and the cold inside of the roof is not enough there may be condensation (the dew point will be reached?) and mold may form on the innermost areas of the paper crete....
>
> I think.
>
> Was hoping some one who knew this stuff better than me was going to reply.
>
> Dan
>
>
>
> --- In papercreters@yahoogroups.com, Pack McKibben <gakayaker@> wrote:
> >
> > I need some input on papercrete roof's.
> > I'd like to know what folks have been doing as far as water
> > proofing. My papercrete roof has, pretty much, always leaked
> > to one degree or another over the years
> > ( http://picasaweb.google.com/owlswamp/HobbitHouse# )
> >
> >
> > After reading "Latex Concrete Habitat"
> > http://books.google.com/books?id=Uu11_JPY83UC&dq=latex+concrete+habitat&printsec=frontcover&source=bn&hl=en&ei=vGtLTNjMOoK78gbt0Ywz&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCkQ6AEwAw#v=onepage&q&f=false
> >
> >
> > I painted a Latex Concrete slury mix over my Hobbit House papercrete roof. No
> > more leaks!
> >
> > My question is....What do y'all think? Do you think the papercrete won't breath
> > anymore
> > and I'm looking at future problems? The LC roof has been on for three months
> > and I
> > don't see any mold.
> >
> > Have you (if you've built a PC roof) been happy with it? What problems did you
> > have?
> > if any
> > PackyMcK
> > PackyMcK
> >
>