MINI-BERGSTEAD Model – 1/24 scale
August 24, 2011 at 4:17 am #14883
If it comes to it, you could use a couple of boards thick ehough to extend beyond the extent of the outside of the dowels. I didn’t note how far the dowels stick out. Rest the shell on the boards on a table with the boards hugging the dowels, and just edge the whole thing off the edge of the table so that one by one the dowels are no longer over the table, but the concrete around them is supposed by the boards, which ARE supported by the table. Then, try gently rapping the dowel out with a hammer.
Be careful not to let too much of the model’s weight hang out over the edge or crash, boom, tears. If you have two tables of identical height that can take the weight, that would be ideal. Just rap out the dowel that ‘s over the gap between them s you slide the model from one table top to the other.. Keeping the boards tight around the dowels would keep the concrete around the dowels supported against the hammer raps. That would, of course, be the extreme, last resort if the little buggers refused to drop out of their own accord.
I like the lexan + holesaw idea, but what kind of adhesive do you have to secure them in place? The killer app of the epoxy is that it will bond to the inside of the hole in the concrete like nothing else. Lexan held in with Elmer’s is an S.O.S. waiting to happen. My recommendation, if you have it or have access to it, is Gorilla Glue. Water-cure expanding glue. That and a plug of lexan the same thickness as the wall is the best solution, I think, short of the epoxy idea.
I have a thorium reactor under the hood of my car. I get ∞ miles per gallon.August 24, 2011 at 3:55 pm #14887
Heres what i had this morning:
the next pic has a lexan circle in the middle window:
the forms are still usable but i need to glue a couple pieces back together before using them again. i ran some numbers using the dimensions of the model and it would def float, if i didnt mess it up
“Leadership and do-ership are not the same thing”August 24, 2011 at 8:33 pm #14897
apart from my own haste, there were 2 major design problems with the my first pour. the dowels soaking up water and expanding made them too tight to remove without a hammer which is not acceptable for such thin walls. the second problem was that the inner form work was not adequately designed to be disassembled after the pour.
to fix the dowel problem, i will just get a smaller size next time. when the cement dries, i will need to use the dowels to reem the holes out to their full size.
while removing the inner formwork today i had to remove the metal tracks from 2 of the wood panels so that i could lean the other 2 sides back and pull them out. i need to modify them so this can be done more smoothly. i hadnt quite thought that through before, so it was a little too rough on the concrete. what i might do is actually cut the panels down the middle before gluing their tracks back on. that way when i pull them apart later on, the panels will be very easy to remove.
im was very bummed when the walls collapsed today so i didnt get much else done. i went to The Reef and had a few beers.
does anybody have tips for how to spread the skim coat on after i redo the shell? what tools? how?
“Leadership and do-ership are not the same thing”August 24, 2011 at 11:12 pm #14903
dont use wooden dowels.
Buy some PVC pipe of the appropriate size and use it to create your window gaps. Not only will it serve exactly the same purpose, but you can even forego removing the PVC window moulds once the frame dries, and just insert and glue the Lexan “windows” right into the provided window “frames.”
Also, while I know you didnt want to use a mesh to simulate rebar or whatever structural reinforcement you will have for a fully sized bergstead, it might not be amiss to cut apart a pack of wire coat hangers and build an abbreviated frame with them. Should you run into more unforseen problems such as with the first attempt, a simple wire-hanger-fram inside the form will do a great deal to give the structure just that little extra strenght to allow for a few knocks and make it more forgiving. I know it isnt neccessary, but it might be a good insurance policy.
As for the skim coat, back when I was doing work with decorative concrete we used a few methods. The best was to use a rather runny acrylic mix (you can buy acrylic pretty easily) and simply “paint” it on with a roller. We would use a lot more given that our projects were quite large (grotesques and such) but with the 1/24th scale model you are making, using a roller and putting on 2-3 coats would be quite enough.
hope this helps, and cant wait to see her in action, buddy.August 25, 2011 at 12:29 am #14905
I’d just like to pitch my blue board idea one last time.
I have a thorium reactor under the hood of my car. I get ∞ miles per gallon.August 25, 2011 at 4:51 am #14909
ya, use ferrocement mesh, can make it quite thin, 0.25cm even, also then can forego a mold,
typically you’d have to have a rebar skeleton, it’s interesting to work with, can lash together with wire. While Ellmer doesn’t seem to use mesh, he does use rebar skeletons for his submarines.
I do recommend that you soften those corners and make them curves, boats are soft and curvy, also it’s easy to make curves with rebar.
calm aware desire choice love express intuit moveAugust 25, 2011 at 11:03 pm #14946
hey guys just to keep u updated; the forms are cleaned and put back together again. i will pour the second shell either tonite or in the morning. i liked Emmett’s idea with using PVC – that was glaringly obvious but thats why we need teamwork. sometimes i miss the obvious stuff. home depot sells “3/4in pvc” but that is the interior diameter. so i grabbed a measuring tape and looked for one that was close to 3/4in on the outside. i ended up going home with copper connectors. i also modified a pallet. and with that i wont ever have to pick it up by holding the concrete itself. i’ll lower the pallet right into the water, and then scoop it back up when im done. there’s also a cereal box in this picture that im gonna use this time for a funnel. and i also cut a strip of lexan to help push the concrete down under the windows.
i think all these improvements are gonna really make the difference this time. i will also pour a second flat surface to use for the top deck. after those are done, i want to build the porch and the stairwells.
let me take a vote:
who thinks i should use chicken wire and plaster over it with mortar mix to make the porch and stairs?
who thinks i should use hardie backer?
“Leadership and do-ership are not the same thing”August 25, 2011 at 11:58 pm #14950
Another suggestion. Pour the walls first, until you are pushing it out the bottom. THEN, pour the bottom of the hull, so you know the corners are continuous.
I have a thorium reactor under the hood of my car. I get ∞ miles per gallon.August 26, 2011 at 5:10 pm #14975
new shell poured and scraped:
rough around the edges but it seems water tight, no cracks. the form came off kinda early and now im getting some bowing at the corners. doesnt look that bad. im off to go run some errands.
“Leadership and do-ership are not the same thing”August 26, 2011 at 9:56 pm #14983
georgeberzParticipantAugust 27, 2011 at 2:46 am #14997
GEORGE BERZ – thnx for the link about PVA fibers – will come in handy if i start producing these bergs!
“Leadership and do-ership are not the same thing”August 27, 2011 at 2:50 am #14996
Ellen, i noticed your math ability on another thread. I was wondering if u (and anyone else interested) would check my math. plz help cuz if im wrong someones foot could get shattered when it sinks. I believe the water line, when i put the concrete shell in the water, will be about 4cm (1.5in) below the windows. heres how i made my conclusion:
B. Volume available below the windows:
distance from bottom of structure to bottom of windows – 12.25cm
length – 62.5cm
TOTAL VOLUME AVAILABLE = 47,852 cu cm = 12.64 gallons
Ability to displace: 12.64 * 8.33 = 105.29 lbs of water before it enters through the windows.
C. Weight of the structure:
1 side = 62.5cm*1.5cm*23cm = 2156.25 cu cm.
All 4 sides = 8625 cu cm
flat bottom = 62.5cm*62.5cm*1.5cm = 5859.38 cu cm
TOTAL VOLUME of concrete = 14484.38 cu cm = 3.83 gallons
Actual water to displace: 3.83*18 (lbs per gallon of “concrete”) = 68.94 lbs
(i also checked to see what concrete weighs by the cu. yd and converted that for the same 18lbs/gallon)
D. Water line height:
68.94/105.29 = 66% of the distance between the structures bottom and the bottom of the windows.
12.25*.66 = 8cm
leaving approx. 4cm between the water line and the bottom of the windows.
DOES THAT SOUND RIGHT?
“Leadership and do-ership are not the same thing”August 27, 2011 at 1:13 pm #15000
gonna have to drill the corners and reattach this with nuts and bolts. after that i’ll seal it with some silicone. the outside will get skim-coated anyway, so u’ll barely see it – one corner will have bumps where the bolts get covered over.
“Leadership and do-ership are not the same thing”August 27, 2011 at 2:15 pm #15001
What is happening is the inherent problems with concrete, no tensile strength… the brittleness… This is exactly the problem I have forseen with large flat surfaces, why initially I wanted a geodesic shape.
I know you said 1/24th scale, is the wall thickness to scale? or just the overall size?
With concrete any kind of curve will increase the effective tensile strenght dramatically.
Also adding the PVA Fiber shown earlier would improve things dramatically as well.
Think about large concrete slabs, like driveways, even though they are 4-6″ thick they still crack and that is unacceptable to a boat.
Have you thought about the total weight of your full sized structure, essentially where the walls join the floor is where all the weight will teeter from and the distance from one wall to the other should be thought of like a bridge, the water will be pushing up in the middle of the structure trying to get into the box, this WILL be significant on a large structure.
Also I believe ferrocement hulls are curved or bowed a bit to help in this tensile strenght area.
sorry about the spelling, checker diedAugust 27, 2011 at 2:50 pm #15003
Thats why I mentioned the coat hangers. Sucks to see shes still giving you problems, but you are all that much closer. Cant wait to see more on her.
Be VERY careful drilling her laterally through the walls. It will compromise the structural integrity of the points where you mount the screws, and it could cause further failures. I fact, I would recommend a different method…
Try taking some of the metal you had been framing with and fit it together at a 90 degree angle, fit two of these into EACH of the corners, even the ones that did not fail, and then mount them into the wall with holes drilled (or use concrete screws). Do you see what I’m getting at? I can email you a quick schematic if you want.
You must be logged in to reply to this topic.
Posted on at