Making a mould for casting concrete

kedwards

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It's that time of year when old garden railway enthusiasts' thoughts turn to, "What can I do on the railway this year."
IMG_3650.jpegMrs Edwards has this planter and I am thinking, if I sectioned it up, it would make very nice G Scale walls. I'd like to make a mould and cast lots of them from concrete. Now last time I did this was way back in the days of the Sandwell Valley Railway when the moulding compound had to be heated up to a high temperature. The moulds I made were very successful and I'm still using the walls I cast on my new railway, but Mrs Edwards' best saucepan unfortunately never recovered from its ordeal.

I understand that the process of mould making is now much easier and that concrete moulds are made by mixing two liquids together. Has anyone on the forum tried this? If so, can you help me? I need to know which stuff to buy as I understand it sets to make moulds of different hardness depending on what you get. Also how to do I calculate how much I need to purchase.

Any help and advice, as always, gratefully received.

Thanks, Keith
 

DickyC

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Hi Keith, Cant help on your request but eagle eyes on anyone else helping out. if you cant get any info you might fancy as day out to this place the chap there is very helpful as its what he sells ! ps while your there take a look behind the sheds in the car park and let me know what you think. (wink wink)

 

kedwards

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Hi Keith, Cant help on your request but eagle eyes on anyone else helping out. if you cant get any info you might fancy as day out to this place the chap there is very helpful as its what he sells ! ps while your there take a look behind the sheds in the car park and let me know what you think. (wink wink)

I will certainly check it out. It's not too far away. I'm intrigued as to what I will find behind the sheds.
 
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GAP

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A trawl through this search may reveal a solution and fill in your day.

My grand daughter uses silicon moulds for making resin things, she just makes a master the mixes ingredients together that when cured form the moulds, they come out similar to the old HO woodland scenics ones and are resusable.

Do you actually need to use concrete or could you use something like render or cementious grout like this, we use the grout to fill voids in road crossings on a 1:1 railway.

I use render for scenery
 
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Paul M

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ps while your there take a look behind the sheds in the car park and let me know what you think. (wink wink)
Steady on old chap, this is a family forum!
 
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kedwards

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A trawl through this search may reveal a solution and fill in your day.

My grand daughter uses silicon moulds for making resin things, she just makes a master the mixes ingredients together that when cured form the moulds, they come out similar to the old HO woodland scenics ones and are resusable.

Do you actually need to use concrete or could you use something like render or cementious grout like this, we use the grout to fill voids in road crossings on a 1:1 railway.

I use render for scenery
Thanks very much. All useful stuff. Your backdrop looks great.
I think I will be using concrete for my walls as won't need painting and weathers naturally.
Cheers, Keith
 

dunnyrail

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2 possible options for you, both tried and tested by myself.

1 would be to use some strong ply, cut out stone shapes from ply (as thick as you want the groves) nail and glue together to give you the size of mould you need then a few coats of varnish. Obviously you will need to make a mould for the sides all smooth, soffit board good for this.

2 I have used a suitable rubber car mat for the stone shape, however this will not give you a random effect if that is what you are after. With this option you make the mould shape then put the car mat in the bottom of the mould.

For the cement mix you need a dryish mix (bit like sandcastles consistency) of 4 parts sharpe sand to 1 part cement.
Put in mould then tip out immediately to dry and do another one. Quick process but leave a few days to dry before using.
 

Tanker man

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Hi Keith
I have made quite a lot of concrete moulds, firstly from ‘Jigstones’ , sadly no longer available but also made my own moulds from silicon as shown below. I use a 1 part cement to 2 parts sand with a good scoop of cementone dye for colouring ( available from Wickes) , this takes a few days to dry but then seems quite strong, once fitted, I line the back with more concrete, to strengthen the wall.
Alec Taranti Is the supplier of many good products, I have bought from there shop near Newbury, as it’s not far from where I live but it appears there there is a branch in Stoke on Trent ( as well as London)
The mould can be cast flat or , by propping up either the sides or the middle, they can be curved, either concave or convex, I just used a piece of rad 3 track to roughly gauge the curve I wanted.
When I make the silicon mould, I use an old piece of ‘Conti’ board, then use double sided tape to fix down ‘Lego’ blocks around the perimeter of the shape I want to cast, leaving a good rim to support the concrete , when making the final item. The Lego bricks are then easily removed , when the silicon is set.
I can post more pictures of ‘bits’ if it would help.
I hope this of help to you
DaveIMG_1529.jpegIMG_1530.jpegIMG_2389.png
 

kedwards

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Hi Keith
I have made quite a lot of concrete moulds, firstly from ‘Jigstones’ , sadly no longer available but also made my own moulds from silicon as shown below. I use a 1 part cement to 2 parts sand with a good scoop of cementone dye for colouring ( available from Wickes) , this takes a few days to dry but then seems quite strong, once fitted, I line the back with more concrete, to strengthen the wall.
Alec Taranti Is the supplier of many good products, I have bought from there shop near Newbury, as it’s not far from where I live but it appears there there is a branch in Stoke on Trent ( as well as London)
The mould can be cast flat or , by propping up either the sides or the middle, they can be curved, either concave or convex, I just used a piece of rad 3 track to roughly gauge the curve I wanted.
When I make the silicon mould, I use an old piece of ‘Conti’ board, then use double sided tape to fix down ‘Lego’ blocks around the perimeter of the shape I want to cast, leaving a good rim to support the concrete , when making the final item. The Lego bricks are then easily removed , when the silicon is set.
I can post more pictures of ‘bits’ if it would help.
I hope this of help to you
Dave
Hi Dave,
Thanks very much for the information, especially the type of silicon mould rubber you use.
I too used a mix of one of cement to two of sharp sand when I did my casting and the walls I produced haven't shown any sign of deterioration in over twenty years!
When I make the mould I will make it water-tight. I can then fill it with water to work out how much mould rubber I need to mix up.
Thanks for taking the time to reply.
Keith
 

Northsider

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I made silicone moulds to cast wall sections for my line. I made patterns using a timber 'armature' (core) which I then covered with a skim of modelling clay. I scribed mortar lines into the clay and textured the surface, before sealing the lot with varnish. To make a split mould, I laid the wall pattern down and set it into plastiscene up to half it's thickness, with 12mm ball bearings pushed halfway into the plasticine too, to ensure the two halves lined up. A perimeter was made of wood, but Lego, as described above, would be better. I then mixed catalyst and resin, let it stand to remove bubbles, and poured it slowly and carefully over the pattern. Once cured, I removed the plastiscene and the ball bearings gave the whole thing a light mist of WD40 as a release agent, and poured the second half of the mould. Once that had cured the mould could be split and the pattern removed. I then made 20-30 cement castings; I still have the moulds for when I need more walls. I'll dig them out and take some pictures.
The walls are just visible in these views:
20220621_161522.jpg20230219_153901.jpg
 

Northsider

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...and here are the photos...

First, the wall in situ. The lean on them is genuine: the station is due a rebuild on new baseboards this spring!
20240130_113338.jpg
Then the patterns:
20240130_113809.jpg
And the silicone moulds:
20240130_113737.jpg
20240130_113500.jpg
20240130_113519.jpg
 

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kedwards

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...and here are the photos...

First, the wall in situ. The lean on them is genuine: the station is due a rebuild on new baseboards this spring!

Then the patterns:

And the silicone moulds:
The walls look great!
Thanks very much for the tips. I'll let you know how I get on.
Keith
 

ThomasDadDurham

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Shame Ive been quiet due to the birth of baby boy no2, or I'd have been straight in with advice, Ive used silicone so much for resin and 'reconstituted stone' (which is just resin with powdered stone in) casting.
The suppliers are usually full of advice, and yes two part RTV silicones (room temperature vulcanising) can be used with concrete. Most of what you need seems to have already been posted.

One tip I will add is you can get colouring for concrete. If doing a one sided mould with blockwork - like your retaining walls plan there - mix a few cups of different shades of grey, and fill alternating blocks in, then before they fully cure, pour the remainder 'filler' in and it should all bond together giving you a more realistic facing.

Supplier wise I use MB fibreglass and TOMPS for RTV, but it seems tomps is now long gone. Same kind of thing as posted above - two part RTVs in big 'paint pot size' tins'. The heat from resin casting is similiar to the heat from concrete curing, so you should get plenty of use out of a mould, enough for your purposes anyway.
 
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kedwards

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Shame Ive been quiet due to the birth of baby boy no2, or I'd have been straight in with advice, Ive used silicone so much for resin and 'reconstituted stone' (which is just resin with powdered stone in) casting.
The suppliers are usually full of advice, and yes two part RTV silicones (room temperature vulcanising) can be used with concrete. Most of what you need seems to have already been posted.

One tip I will add is you can get colouring for concrete. If doing a one sided mould with blockwork - like your retaining walls plan there - mix a few cups of different shades of grey, and fill alternating blocks in, then before they fully cure, pour the remainder 'filler' in and it should all bond together giving you a more realistic facing.

Supplier wise I use MB fibreglass and TOMPS for RTV, but it seems tomps is now long gone. Same kind of thing as posted above - two part RTVs in big 'paint pot size' tins'. The heat from resin casting is similiar to the heat from concrete curing, so you should get plenty of use out of a mould, enough for your purposes anyway.
Thanks very much for this useful advice. I will let you know how I get on.
Keith
 

ThomasDadDurham

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Thanks very much for this useful advice. I will let you know how I get on.
Keith
The only reason I hadnt started making cast retaining sections myself, is I'd planned to use these kind of outdoor tiles "split-stone mosaic" - whenever Im on the nearest industrial estate I trawl all the discounted and clearance tile places, Im sure I'll find a job lot of a suitable colour and size eventually. It's more of a 'that'll do' solution than an accurate scale model, but outside of the stations and villages I wasnt going to be too fussed. Just letting you know they exist, and you can get outdoor grout.
splitstone.png
 

SevenOfDiamonds

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Since we are drifting away from the original topic, somewhat, I have bought one of these rectangular planters to experiment with . . .

1707923759560.png

The courses are about the right depth for G Scale walls. Some of the "blocks" are over-length, but overall giving a fair impression of a stone wall from a distance. Dimensions are 60 x 25 x 25 cm.

Cut in half (30x25x25), and used upside down, it would make two bridge piers. It could be cut into flat pieces to use as retaining walls of a variety of heights . . . or (getting back on topic, almost) used to form a mould to create concrete "copies".

I bought mine from B&M Homestores (£18.99) but I have seen them in Aldi in the past (though in a plainer grey, rather than the more mottled one pictured). There are also Square ones (both cubes and tapered versions). Search for "Slate Effect Planers".

Cheers

David
 
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kedwards

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Thanks to both ThomasDadDurham and SevenOfDiamonds for their suggestions/ideas. As I work my way around the railway both the tiles and the planter could be used in different locations.
Please keep the ideas flowing. I'm sure others will be interested too.
Meanwhile I will pursue my idea of making concrete moulds from Mrs Edwards' planter.
I will let you know how it goes.
Thanks again.
Keith
 

David1226

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No, but at 145mm (and that may not be the longest) that scales out at over 10 feet (@13.5mm to the foot)!
I guess that could be rectified with a little bit of extra scribing.

David