Taking a silicone mould of a pier cap?!

[jamestplunkett]

My neighbour and I are restoring the original iron railings at two houses in Hackney. His house still has the original brick pier with a nice pier cap on top. Outside my house we have had to rebuild the pier from scratch and now I'm wondering how best to replicate his pier cap.

I've looked online and can't find any pier caps that even close to the right size or shape, and he's obviously keen to keep his original pier cap. So - I'm wondering if I could take a mould of his pier cap and pour my own custom cap with concrete?

After watching a lot of Youtube videos, it seems like silicone would be the way to go. My plan is to make a wooden frame around his pier cap and then pour silicone over it to make a mould. Then I would remove the mould and fill it with concrete to make a replica pier cap.

Does anyone any advice on whether or not this would work?! Is silicon the right material for the mould? Would it be strong enough or would the weight of the wet concrete distort it?

I don't mind a bit of trial and error. My main worry would be whether the silicone would damage my neighbour's pier cap.

Thanks!

 

[Tigercubrider]

Yes, with a bit of work.
plenty of videos on concrete moulding online.

what i would do (unseen) would be to make a wooden collar around the pillar, then base your mould off that.
a sort of datum point.
people often make the mould out plastic faced furniture board for a clean release.
when you make the cast out of concrete, it also needs a wooden frame as support
quite often people use a few screws but mainly silicone to stick the timber together

 

[Old Salt]

You could use newspaper and wallpaper paste to cover his pier cap before moulding. It would be easy to remove after moulding.

 

[Tigercubrider]

Or clingfilm.
silicone copies tiny detail so no wrinkles
pallet wrap might be better

 

[conny]

Lay some layers of cling film across the top of the pier cap, First from side to side then from front to back, making sure the layers overlap each other. Next form a tight box around the pier cap to a height about 50mm taller than the cap. The box can be secured in place by resting on support posts below the actual cap. The posts can be bound to the pier with a few turns of sticky tape to hold them upright.
Next mix up a batch of plaster of Paris and pour it gently into the box frame making sure it goes into all the corners. Fill the box until it is level with the top of the box, (which should be about 2" higher than the cap), and allow it to set for a few hours.
When you are sure it has set, gently remove the box, either by lifting it up or taking each side off in turn. You should now be left with a 'negative' cast impression of your neighbours cap. Replace it back inside the upturned box you used, (you will have to re-assemble this if you took it apart).
Now you can mix up your concrete so it can be slowly poured into your mould. You shouldn't need to line the mould as the plaster of Paris will break away once the concrete has set. Any traces of plaster can be washed away with water and a stiff brush.
You could insert some steel rods into the base of the new cap to bed into the cement when you mount it on the pier.

 

[Tigercubrider]

The OP asked about silicone - hence my reply
But plaster would be a lot cheaper.
if using plaster, once you have a bit of coverage on the surface, use some burlap (cheap sacking) as it adds reinforcement