Concrete T-rex




About: Woodsman and field tutor on a week day. Life long inventor, designer, engineer for the rest of the time. From items that make life easier to items with no reason to be....other than the idea popped into my h...

I needed to come up with a fossil related activity for kids when I happened upon a set of sand pit moulds of a T-rex, I I also had a ply board with lots of de-lamination... which looked a lot like sedimentary rock formations.

What was needed was something to put into the moulds that looked like stone.... that would be concrete then!

Step 1: Base Board

After laying the body parts out and drawing around them I cut the base into manageable pieces.

I filled any big cracks and made the wood look as much like rock as I could.

Step 2: Casting in Concrete

I mixed the cement, sand and water with some PVA glue to toughen it up a bit.

Wood screws were driven into the base board and joined up with wire to hold the concrete in place, the moulds were packed hard with the mix, pressed into place and the moulds removed.

Step 3: Fossil Jigsaw Ready to Go!

Once it was all dry I sealed the surface of the concrete with more PVA and then off it went to my work place to be used.

I was quite surprised at how long it took the kids to assemble it, it was very much a hit!



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    7 Discussions


    3 years ago on Introduction

    This is a cool idea, but the execution of it is poor.

    Firstly PVA glue will make your concrete weak

    Second fixing concrete to a plastic mould will result in it chipping off with in a week or two.

    I would suggest lining the mould with fabric reinforcement (it looks like the stuff on the back of those tile sheets) and using a 1:3 cement mortar( 1 part cement to 3 parts sand) and covering the reinforcement with the mortar, about 15-20mm thick.

    Next you must cover the mould with a damp towel and put it in the shade to let it cure (about 24 hours)

    Finally you must fill the rest of the mould with a light weight concrete mix. I would suggest a 1:2:2 20mm stone mixture with aerator admixture ( 1 part cement to 2 parts sand to 2 parts stone). The same curing protocol must be followed.

    For the finishing touches drill holes in the back and mount them to the wood boards with expansion bolts.

    1 reply

    Reply 3 years ago on Introduction

    It did what it was designed to do and entertained the children who came for the day.
    Since then we have decided to offer the session to schools, I have replaced the concrete with resin for longevity.
    So, as to it being poorly executed agreed, it only needed to last a day which it did, job done :).


    3 years ago on Introduction

    Theres some stuff you can get for doing decorative concrete work called silicon spheres that mixes with the concrete to make it lighter and brings out the detail. It would work very well with this type of thing. A cement bag size of this stuff weighs next to nothing and as a bonus if you mix it with paint and paint your roof with it,the temperature inside your house or shed in summer will drop like you wouldnt beleive.

    I used to work for a company called Cost of Wisconsin, we did themed construction, so a lot of concrete mold-work... Anyway, we had this really talented sculptor in one day, and he mad us this awesome like, 5.5foot x 3foot t-rex head that we made a bunch of molds of. They couldn't sell them for a while, then someone put one at the bottom of a sandbox, and now they sell like hotcakes. ;p

    Here's a link,

    One of my all time favorite jobs, you gotta check some of their work. :P