No thoughts at this stage Cliff, but if all goes well I’ll chat to other club members to see where it might lead - even cost share would be good. To be honest latex isn’t the best medium (I’ll get to that bit soon), silicone is way better but costs around 8 times the price - if you can even get it…
Uhh huh, I’m with you on that! 
Same here. I hauled most of this pile close to 10 years ago, it was tough then. Looking at them now I have no idea how I could move and stack them easily. No hydraulics unless I hire and that costs a bunch.
There should be a local service called “3 Starving Bodybuilders and a Truck.”
Molding is all done, no particular surprises. Somewhere around 25 – 30 layers on these all up.
We’ve moved into summer proper now, temps in the 70’s and 80’s most days so I was getting 3 coats done in an evening, and up to 8 on a weekend day. Two weeks work to get to this stage…
Since latex is no good for filling in undercuts, even using thickener, thought I’d get clever and try using urethane rubber (proper name) – Smooth On 40 as a fill layer where I needed it. Claims to stick to vertical surfaces and mostly lived up to what the label said.
I did the big undercuts in several coats and got what seems to be a good result… Longer term is – experimental. Different expansion & shrinkage rates might cause separation of the layers but I tried to do a pretty good sandwich between two layers of latex.
The price of this stuff in NZ is eye watering. If I had a choice I’d do the whole mold in Rebound and smash it out in 1 day, but this would have tipped the cost to over $1000 – just in rubber. Never mind that it’s Out of Stock in the whole country. The Latex cost me $150 for 8 litres (2-ish gals). Big disadvantage is the number of coats, and the time it takes.
I’m leaving this lot for a week to fully cure before adding the glass layer.
I’ve think I’ve done enough research on GRC to know that it’s possible to do what I want, but finding the materials in New Zealand has been – expensive (again). Many online clicks later and I now have the two hard to get ingredients: 10 kg Alkali Resistant Glass Fibre & GRC Acrylic Polymer.
Cheers
Neil
Same issue here on the northernmost corner of the Polynesian Triangle! We were lucky to find abandoned lava stone from various yard projects around the neighborhood to make the scenery for our little layout.
Eric
Well done with that Eric. Nice and light (ish…).
Cheers
N
Sneak peek - first two demolds. The blue is the urethane rubber where I filled in the undercuts.
Cheers
N
Niel,
I used preformed molds from Bragdon Enterprises. They have a wide variety of shapes, sizes, and rock formations. The molds are pretty thin so I used a Casting Bed (aka a plywood bed with 2x4 edges to hold 3 inches of sand inside). I laid the mold on the sand and pressed down on the areas that needed to stand out. If you don’t do this you will end up with a flat mold with reduced detail. I also built up sand curves were needed to allow the casting to bend where needed). I used stucco mortar for my castings.
2 MUSTS
Hi Jim,
Thanks for chipping in - Bruce’s pics of your layout kick started this little brain fart of mine…
The sand bed is a great idea. I’ve captured the original form of the rock using the figreglass shell, but changing it up with a different backing shape gives a whole lot more. Mind if I borrow it? 
Read and hear ya on the reinforcement and those pesky air bubbles. I’m trying glass fibre at the moment - will report how it goes.
Don’t suppose you’ve got any pics when you were making your panels?
Cheers
Neil
Neil,
Borrow at will. Photos to come…have to find them
Jim
Casting Bed - top 2x4 is for a tarp to cover if raining.
I recall hearing that resting a vibrating finish sander against the mold will assist getting the bubbles out. I think it was from the guys casting concrete bridges.
I’ve been following along with this and others like it in preparation for mine. But this seems very involved to the point that I wonder if it would just be better/quicker/easier to plaster in real rocks big and small. But maybe I’m missing something due to my lack of experience?
Hi Mickey,
Not at all. It’s probably more involved than I expected, but I kinda roll that way…
My last railway was on the ground and thats what I did - embedded them in crusher dust. Managed to get some quite realistic cliff walls in some spots.
This time I’m going to be building on waist high bench work - so I need to be lightweight. That’s where thin shell concrete / plaster comes in. It’s probably not for everyone - and if you can get some molds at a good price (like the Bragdon ones Jim used) it’s gonna be a lot easier.
I need something like 30 sq yards of rock face. That’s why I’m going big with the molds.
Cheers
Neil
Niel,
Some beautiful work! VERY nice and realistic.
Here’s the tool I made/adapted for use in getting bubbles out of the castings.
It has to be moved all around the mold. I also used tamping with a trowel as the final step.
The most interesting part of molding this time was setting up a 2 part mold to do this rock. There were too many irregular angles to try and do it in 1 piece and expect it to come off.
Best idea I found on the web was to use label stickers to build the ‘wall’ between the two halves.
Most videos I watched talked about doing the two sides separately but I couldn’t see the point to be honest – the stickers were going to form the split and were disposable. I did the whole lot in several layers, with extra build up where the ‘bolt holes’ were.
Then drilled the holes, and cut the excess fibre glass off with a grinder. Bit of prying and I had the two halves.
First concrete casts went in this arvo… 
Finally! I’ll share more once I see what they look like in a day or so.
Cheers
N
I couldn’t wait 24 hrs…
Broke open the first one at about 20 hrs. Disappointed to say the least – lots of air bubbles.
Second one came out better – way less but still enough bubbles to be annoying. Third one was a charm, just a few pinholes.
I think I was rushing at the beginning and just wasn’t careful enough. Day off tomorrow, going to do a full brew and take a few in progress pics.
Cheers
N
I know it’s easy to see flaws in your own work, but honestly, I really had to look closely to find the bubbles. I think once painted they won’t be noticeable.
I think they came out great.
And don’t some rocks have air bubbles? Think missing fossils.
Just use a screwdriver blade to chip out the bubble and once painted/stained you will never see a thing 
