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Discussion Starter · #1 ·
My Alvarado Hotel used sheets of vacuum formed plastic tile for the roof.

The Alvarado as built




The roof did not stand up well in the hot sun of New Mexico so I wanted something more durable.
Roof damage



On MyLargeScale I had seen a mention of something called ShapeCrete which can be bought on line and delivered to Home Depot. It can be molded by hand like clay or cast in a form. It looked like something that I could use to make tiles for my buildings so I ordered some. There are several tutorials on line showing how to use it in addition to the instructions on the tub it comes in.

I decided to make a couple of test pieces to see how they worked and determine if I needed to make any changes in the process. A 3 X 8 inch form box was made of cardboard and tape.


A piece of the plastic tile was inserted upside down to form the contour of the casting. (The weights and “c”-clamp were to keep the box from bulging)



A backing was made of corrugated plastic and painted with concrete bonding agent. This was added to give the cast part more strength.


I filled the form with Quinoa to get an estimate of the amount of cement I would need.


To make the tiles the cement powder was mixed with water to a consistency of pancake batter so that it could be poured into the mold. I made a couple of test pours to see how they worked, the first with just the cement and the second with color added and a slightly thinner profile. While the cement was still wet I pressed the piece of coated corrugated plastic into the cement.


The first pour I did not use any mold release and it was hard to de-mold.


The second one I used some cooking spray on the mold and the casting came out very easily. The first casting is 3/8 inch thick from the top of the tile to the bottom of the concrete. The second one is 5/16 and with the plastic backing, both seem plenty strong.



In the future I will use a vibrator to remove the bubbles from the cement. Now I am ready to try casting roof sections for the Alvarado. The largest section will be about 11 ½ X 15 inches and it will take 2 pieces to form the largest roof section. My original thought for the smaller parts was to cast the sections and then to bend them at the roof peak while the cement was still soft but that didn't work very well. I will post more details as I progress with this new roof.


 

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Magnificent station Winn, and out here in Australia the sun is also not kind to vac formed plastic either so I am interested in this project as you find out how this stuff works. I like the idea it's a cast "concrete" and having the colour in the mix make the tiles look real, better than paint and should last.
Not sure if I can find the Shape Crete down here but very interested in how it comes out and how you think it might last. A few questions you can answer as you go along, is it heavy, can you make large sheets, how do you join the sheets of cast and is it brittle.
Thanks
Russell
 

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Discussion Starter · #5 ·
I thought I posted a note yesterday but I guess I forgot to hit post! That happens to OLD GUYS like me. I will be casting some roof parts next week and will post my progress. If the weather doesn't improve it will be a while before I can start installing roof sections.
 

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You can use a jig saw with out a blade to remove the air bubbles.
Just hole it in place on the table and turn it on.
The bubbles will come to the top/bottom of your mold.
 

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Discussion Starter · #7 ·
Yes, I actually do that with a big orbital sander. It works quite well but my last casting still had some small bubbles even after vibrating for about 3 minutes. I'm wondering if vibrating the mixing bucket before pouring the cement into the mold would do any good. I have enough panels done now to reroof the south wing. I have been working on too many things lately and haven't had the time or energy to post what I have accomplished. I'll try to get something posted soon.
 

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Discussion Starter · #8 ·
Casting tiles part 2
I have progressed to casting roof panels. A mold box was built using a plywood base and wood strips screwed to the base.

A piece of the plastic roofing was fitted into the mold box with the bottom side up to form the surface shape of the cast cement. A screed was made that would the level the cement below the edges of the mold box the thickness of the corrugated plastic board.


The mold was placed on top of a foam pad and after filling with cement was vibrated using a sander. Then the plastic board was placed on top and filled around the edges with more cement.


After the casting had set overnight the box edges were removed. The edges of the plastic form were not tight enough against the box edges and allowed the cement to run underneath.


This had to be removed before the form could be released.


This is the roof panel after removing the plastic form.


Here is a photo of the new roof panel in place on the Alvarado.


The first try at casting a roof panel was quite successful. The leakage around the edges of the form was not good and it was difficult to remove it from the casting. The next part of this write-up will be efforts to make the casting process easier and quicker.
 

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Looks about the same as Cement All, except my curing times were hours, not over night.
 

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Discussion Starter · #11 ·
Jon, did you use that cement over a foam base? One thing I like about the ShapeCrete is that it contains fine fibers that make it quite strong. After 3 or 4 days of curing even 1/8 inch thickness is easily handled without breaking.
 

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No Win, I poured into open forms. Each arch on the curved section was done one at a time. Rain gutter nails were used as rebar to hold them together.
I didn't do any thickness tests. Cement All has an additive to reduce water during casting.
It did suffer one cracked leg when a trailer was backed into the layout and it's section hit the ground. Otherwise it sits fine. I admit it's a tad crude, I had a vision for the curved arches, then I needed a use!
I mixed stucco color into the dry cement for a uniform tint.

I wonder if you mixed to clay like consistency, if you could push sheets of it, firmly into the mold, with a rolling action to eliminate the bubbles ...
 

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Discussion Starter · #13 ·
Finally I will continue my description of casting concrete tile for my hotel.



Casting tiles part 3


I will now describe my efforts to make the molding process easier and faster. I had material from MicroMart for making rubber molds so decided to use that.


The mold box that was used in the previous casting was used again. This time the plastic panel was inserted with the top side up. Molding clay was used to seal around the edges.


The mold ready for pouring in the liquid rubber.


The 2 part rubber was mixed and poured into the mold. I used all of the two 16 ounce parts.


Rubber mold ready to pour concrete.


After pouring the cement into the mold and vibrating until level and bubble free, the corrugated plastic board was set on top and the edges filled. After letting the cement set up the excess cement was wiped off with a damp sponge.


Here are the first and second casting side by side. The second one using the rubber mold was much easier to demold. After unscrewing the mold edges the rubber mold and the casting could be turned over and the rubber mold just peeled off. I am still getting some small bubbles so I need to work on that. More vibrating helps and wetting the mold with soapy water was suggested. I haven't tried that yet.


The next chapter will describe how the cast panels were used to build a new roof on the Alvarado.
PS I did try using soapy water to break up the bubbles. It didn't work as it just beaded up on the rubber.
 

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Discussion Starter · #14 ·
Casting tiles part 4


Originally I planned to cast parts the shape and size that were needed for each application. The following are examples of the process.


Making a shortened panel. I installed a dam across the mold and caulked the gap with clay.


The short panel after removing from the mold.


This panel and the original full length panel are enough to span the full length of the upper roof.


This is the original roof showing the warp damage and the intersection of the end roof and the middle roof.


To create the intersection of the end roof and the middle roof I installed this filler in the mold.


This is the resulting panel with a triangular cutout. It is shown with the peak of the ridge-line being cut flat so the ridge cap will fit better. I used a thin masonry blade on my table saw for cutting. More on this below.


I thought it might be easier to cut pieces to the size and shape I needed. I tried cutting one of my original trial pieces with a masonry blade on my angle grinder. It worked well with no cracking or chipping of the concrete.
I found some 7-1/2 X 1/16 inch masonry blades at Harbor Freight that would fit my table saw. They worked well for cutting full panels to the size and shape that I required.


Here is a saw cut panel installed at the vee of the cast roof junction.




I installed aluminum flashing under the valleys between the roof parts.


All the roof panels installed on the upper roof of the south wing.


All the porch roofs were saw cut to size.


I tried to cast concrete ridge tiles in a mold made of molding clay. They proved to be too fragile.
The shape in the lower part of the photo is a wood form that I used to make the mold. I decided to use that for the ridge tiles instead of the concrete.


I turned all the ridge tiles from 5/8 inch dowel with my lathe. The large diameter came out about 7/16.






I then cut off a little less than one half the diameter using the table saw.
A REMINDER!! ACCIDENTS HAPPEN EVEN WHEN YOU THINK YOU ARE BEING CAREFUL! I was pushing the pieces through with 2 push sticks and still managed to slip and cut a ½ inch piece off the side of my left thumb!


A better way to do it is with a band saw. Not quite as accurate but much safer.


Now some photos of the finished roof of the Alvarado.


West face
This doesn't show much difference between the old (left) and the new roof but viewed in person there really is quite a difference.


South end


Porch roof


I will need a couple of more buckets of cement to do the north end of the building. There also a number of details which need some TLC, but this is the end of this article.
 

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it's a pleasure to see this giant model looking decent again.

thank you for the detailed description of the methods used.
they will be helpfull, if i ever come around to build my planned mexican village.
(apart from the "how to cut flesh". i already knew that one)
 

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Wow! Way to go! It looks great and I agree with korm, the Old Lady looks great with her new Doo!
 

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Wow, finally something I could do with Quinoa!! Seriously, that is some great castings. Maybe a tip for the ridge piece. My dad was a shop teacher and he had a cool way of doing split turnings. Start with a square piece of stock (Glued up as needed) and then Split it in half on the table saw. Put glue on both pieces and put it back together but put a layer of paper towel in between the pieces, he had those thick industrial brown ones. After that dries you chuck it up and do your turning, suggest leaving a square section on each end in case you want to do any saw work. When yer done turning, you hit that seam with a chisel and it will split right open. If you wanted to make a V in the bottom to span the peak, you could make a couple passes on the table saw with the blade set very low and tilted at roof angle. To make it easier to feed, you could attach a scrap board from end to end at the previously mentioned square parts and run that against the fence.

Notes: This method predates Gorilla glue so prolly best to use Elmer's. Also if you are worried about the pieces separating at speed, run a screw thru each end in the part you are leaving square.
 

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Discussion Starter · #20 ·
EDH, interesting method. I tried to order more ShapeCrete to do the other end of the hotel but found that I can no longer get it. I tried all the sources listed on the manufacturers website with no luck. I emailed the manufacturer and got no response. Instead I tried some vinyl patching cement and it seems to work well even with thin pieces. I think that is what JigStones recommends. It is about 1/4 the price of the ShapeCrete so I dispensed with the corrugated plastic backer and just cast the panels full thickness. That seems to work well. So on to finishing the roofing project.
 
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