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placitassteam 12-21-2019 12:57 PM

Casting roof tile with ShapeCrete
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 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.

ferroequinologist 12-21-2019 09:00 PM

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.

Oliver Jake 01-15-2020 05:48 AM

Amazing Research about the Roof and it will protect about the Roof and sheet will be protected and houses will be safe.

kormsen 01-15-2020 02:47 PM

that looks very interesting.
i hope to read more about it.

placitassteam 01-16-2020 06:33 PM

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.

jimhoot 03-17-2020 07:35 PM

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.

placitassteam 03-18-2020 11:15 PM

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.

placitassteam 03-20-2020 04:12 PM

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.

kormsen 03-20-2020 11:50 PM

that is interesting.
thanks for sharing.

Totalwrecker 03-21-2020 04:20 PM

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

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