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Re: [PSUBS-MAILIST] milestone



Brian Cox wrote:

Well if you must know... I guess I can take time out of my busy day.  You
know I don't like going on and on about my sub. ( just tell me to shut up if
you've had enough)
No, no - loquacious is good in my book. I've been interested in FC and concrete boats since my early teens, but have yet to actually build anything. When I do build something, I want it to come out right, so I collect as much info as I can from people who've done it successfully. 


8 total layers of 22 gauge galvanized hex netting.  The hex netting is the 1
inch aviary netting.  That is 4 layers on each side of the rebar or the
internal armature.  I basically followed the same proceedure as how one
would build a ferro-cement sailboat.  Since the shape that I built was
relitively small (21 ft long), and only 8 ft wide at the widest point I
probably could have gotten away with not using ribs inside but I figured
since there was going to be some unique stresses on this thing I went ahead
and built just like you would a sailboat.  I even spaced the ribs closer for
additional strenght (18" OC).

I have some pics of my early construction on my web site.


I'll go look. I'm especially interested in how you formed the ribs.


Anyway,  using the ribs is better anyway because it gives you a framework to
tie on the stringers.  The stringers are 1/4 inch hard drawn wire - it has a
spring to it so you can bend it to make a nice curve. Those go on at about
3" apart.  They get tied on with wire ties. Then you have diagonals, which
are 1/8" hard drawn wire which go on - you guessed it - diagonal to the
stringers, this is so that any irregularities in the shape tend to get
smoothed out, so you have clean lines.  Once all that is all wired on then
you're ready to put on the netting. - with millions of more wire ties - can
you say carple tunnel syndrome !

Once everything is hunky dory and all the mesh is nice and tight you are
ready to plaster !  I used a mix of 1 part sulphate resistant cement (most
all cement is) to 2 parts sand.  You can't just use any old sand.  You need
to look for jagged shaped sand, you don't want to use round river sand.  The
reason is that you want it to key together really good.  I talked to a
concrete expert and he clued me into this sand over in Soladad Canyon where
it is blasted out of a rock quarry and ground up into sand.  The other thing
is you also want an gradation of sizes of sand particals, not just all one
size.  The specs that I got on the make up of the sand from Solidad canyon
was practially a text book perfect sand that I needed.  You want to try and
hold the thickness to around 1 inch.
So you're on the "sharp sand" side of the argument. Others argue that washed and graded round sand gives equally good strength on cure and is much more workable when applied. 


I hired some plasterers on the first round and let them do their thing, I
was very nervious because I was very concerned about the water content and
getting the mix right. But I just let them go because there is the practcal
side of it also, ideally you want a low water content but it's very hard to
get the penitration into the mesh if the plaster is too hard to work with.
So you may have to sacrifice a few thousand psi strenght factor but you are
getting better penetration and ultimately a better finished product.  The
top part of the clamshell I did myself with some extra help and everything
went well.
There are additives that are intended to improve workability and allow a low slump mix to be used. Fine silica (pozzolan) seems to both improve the strength of the final product and make it more workable, but there are also a bunch of commercial products intended only to make a low-water mix workable. I think sodium stearate is one..? Anyway, you didn't use any of that, I take it. 

Thanks for taking the time to lay this out.

Best,
Marc



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