Picked up a copy of Model Military International #3 from MegaMags on Queen St this week.

I have to say if anything is going to tempt me into larger scale military modelling it’s the articles in this magazine. Really there’s only two things stopping me (cost incidently isn’t one of them)!

1. I have no idea how to paint convincingly at this scale without the use of an airbrush which I don’t own.

2. The amount of detail involved in even the basic kits (without aftermarket add ons) terrifies me!

Anybody taken the plunge into 1:48th, 1:72nd scales recently? Any pointers/tips/suggestions for a rank newbie?

Continuing from our previous post about mold making…

11. Checking the mold is set.

Once you’ve waited long enough return to your mold and examine the dregs in your mixing pot. You can see in the photo I’ve peeled almost all of the dregs out in a single piece so it’s clearly fully set. Once set RTV is a very flexible vulcanised rubber that you can stretch out quite some distance before it snaps.

Since ‘Ultrasil’ has an 8 hour recommended curing time and I left this mold overnight for about 22 hours, I would expect it to be set.

12. Removing the pour box.

After rolling the Klean Klay back and saving it for another mold, peeling back the masking tape and carefully tearing the foam card walls away from the mold I’m left with this: a block of RTV clinging tenaciously to my glued down masters.

Click on the photo and you’ll see some RTV has snuck under the edges of the foam card and was stopped by the masking tape and/or Klean Klay. This shows you how easily RTV can escape from an incompletely sealed pour box. I usually trim this off with a sharp Xacto before peeling the mold away from the base.

You can also see there’s a lip of RTV standing proud from the mold bottom as well as several set drips. I cut these away when I bevel the edges of the mold with the same Xacto to make the mold bottom reasonably flat.

13. Removing the mold.

You need to be careful removing the mold from the masters because if you’re going to damage anything it’ll be now. I slowly lift the first edge away from the base and then work at rolling the mold off the masters from each side a little at a time as in the photo. Eventually the mold should release itself from your masters, popping right off. Don’t be afraid of bending the RTV mold back 90 degrees or more while doing this as set RTV is very flexible.

Some people will recommend you coat your masters with a mold release product before pouring the RTV to aid removing the final mold. As I brush on the first coat of RTV in all my molding (and this tutorial) I believe the use of mold release may be a little redundant.

However if you want to try it I’d suggest picking up a spray can of mold release. Avoid using any kind of brush on product (some tutorials I’ve seen use vaseline) as it may unintentionally add an additional brush stroke texture to your masters! We use RTV for molding because it is very good at picking up minute surface details after all.

14. Tidying up the mold.

Ah the perils of tutorial writing! While removing the mold two of the smaller masters snapped off the base, remaining in the mold as you can see.

Click the photo and you’ll also see RTV has got under a fair amount of one master edge as well. This highlights the point that there’s a trade off between really gluing your masters down to your base, sealing all their edges and actually getting them off the base ever again.

As I mentioned in the first of these posts I opt for a weaker bond with the base as I often reuse my masters later on, possibly in different layouts. However that does mean that this particular problem can occur. Fortunately it can easily be solved by popping the stubborn pieces out and then trimming away the excess RTV with a pair of fine scissors. I use both straight edged embroidery scissors (borrowed from my wife’s sewing box, ssssh!) and a curved set of nail scissors for snipping away excess RTV.

15. The finished mold.

There you have it! Your mold is ready for casting and I hope you’ve enjoyed this rather long tutorial. Feel free to post questions or comments and I’ll answer them as best I can.

If you’re considering casting your mold in a hard plaster product like Hydrostone or Ultracal 30 you may be interested in a much earlier post about the plaster casting technique I use to produce the 15mm wargaming terrain for sale on this blog. I may also publish a photo tutorial of plaster or resin casting in the future so keep an eye out.

Continuing from our previous post about mold making…

Estimating the Mold Volume and Mixing RTV

4. Assemble your materials.

The RTV product I use is called ‘Ultrasil’ manufactured by Barnes, an Australian company and available from TopMark in New Zealand. I’ve also grabbed a small previously set mold, a cheap hog bristle brush, a permanent marker, a clean pot to mix RTV in, a mixing tool (cleverly disguised as an HB pencil) and a large 1L bottle of beach sand. I’ll describe the use of each below.

Ultrasil is a 1:10 RTV (room temperature vulcanising) product consisting of a large pot of white rubber and a small bottle of blue hardener. I’d seriously recommend purchasing RTV products with coloured parts like this, because mixing a 1:10 product by weight when both components are white is an absolute nightmare. Particularly when one of them is a thick, sticky, viscous rubber. Having a coloured hardener also makes it very easy to see your RTV is fully and uniformly mixed prior to pouring which is obviously important.

However the real beauty to a coloured hardener is you can mix all of your molds ‘by eye’ using colour matching to determine when you’ve got roughly enough hardener into the mix to guarantee a set mold. This saves you measuring anything and is fast and reliable. I’ve mixed roughly 30 molds this way and only botched one early pour.

The only down side to this method is you tend to over use hardener which could lead to you running out. Although that’s never happened to me. I suspect Barnes gives you excess anyway in anticipation of most molders being lazy devils and mixing by colour. Varying the amount of hardner added will change the working time and final strength of the set RTV, but most of these products should have an ample working time anyway. Definitely check the MDS (material data sheet) for your products before mixing them though.

5. Estimating mold volume using sand.

RTV is an expensive product here in New Zealand so I want to waste as little as possible. This means I need a way to get a good measurement of the volume of RTV I’ll need to fill a given pour box. The easiest way to estimate the volume is simply to pour some other ‘liquid’ into the assembled box.

Water springs to mind and I know at least one professional caster that does use water for mold volume estimation, but to me water is far too messy and makes your masters and pour box wet! So I use good old washed and dried beach sand (nabbed from Whangamata several summers ago).

Take your sand and fill the pour box with it, completely covering the masters and then some. Gently shuffle the box around until the sand is level then take a tool/finger and poke around in it until you hit a master. Do this to make sure your masters are buried sufficiently deeply - like the external mold walls you should be aiming for 4-5mm of sand covering the highest point of the tallest master in the box.

6. Marking the mixing pot.

Once you’re happy the sand sufficiently fills the pour box, gently pour it out into some large container (I left that out of the above photos) being careful not to lose too much onto your work area. Pour the larger container into your mixing pot and mark where the sand fills the pot to. This is how much of the basic rubber component you’ll need to fill your pour box.

Tip the sand out of your mixing pot and brush any extra grains out. You’ve also got to clean any extra sand out of the pour box. I use a combination of gentle shaking, blowing and brushing off the masters with the hog’s bristle brush. It’ll only take a couple of minutes to clean up and you’ll have a dry box ready for filling with RTV.

7. Mixing RTV by colour matching.

Finally we’re ready to mix! Carefully pour the white rubber component into your mixing pot until it’s been filled to the mark. This can be a messy process and I find it handy to have a scrap of foam card nearby to scrape the edge of the rubber pot clean before putting the lid back on tightly.

I believe RTV products like these can be degraded by exposure to air moisture so don’t leave the lid off your rubber pot for longer than required. The shelf life of an opened pot may be reduced too, so it’s often a good idea to plan and pour a series of molds together in order to use your RTV up in a reasonable space of time. Discuss these details with the manufacturer/reseller when you purchase your RTV.

Add hardener a fair amount at a time and thoroughly mix it in with your mixing tool. Be particularly careful that you mix in the white rubber on the sides and bottom of the pot. I find it handy to use transparent or semi-transparent mixing pots for this reason. I have a cat and a three year old in the house so have an endless supply of plastic pet food containers and jelly pots that get seconded to the garage once empty and cleaned.

Compare your mix to any set mold you have handy. Mix in more hardener until you have a rough colour match to the set mold. Always keeping in mind that a mold that’s seen a lot of either resin or plaster can get a little lighter in colour.

Of course if this is the first mold you’re mixing then the above paragraph is a little useless. In this instance I’d recommend either following whatever instructions came with your RTV or use a roughly regular shaped mixing pot (no curves or sloped walls) and dividing the space between the bottom of the pot and the ‘fill’ mark into 10 roughly similar proportions. Fill nine of those with white rubber and one of them with coloured hardener then mix thoroughly. If anything you want to be a little too generous with the hardener for your first mold, just to make absolutely sure the RTV will set. I’d also suggest your first mold pour be reasonably modest in size. For future molds colour match to your first one as appropriate.

Pouring the Mold

8. Brushing on the first RTV coat.

Now you have a pour box and your mixed RTV ready to go you may be tempted to just slop it in and leave it to set. Beware! For this will almost certainly lead to trapping air bubbles in your masters and related annoying blobs appearing in any casts you make. ‘Act in haste, repent in leisure’ as they say, and remember that air bubbles are the garage caster’s nemesis.

Without fail, I always brush the first coat of RTV over the masters by hand using the stiff hog bristle brush you have handy. Brushing the first coat of RTV on like this will reduce the chances of trapping an annoying air bubble somewhere on the surface of a master. It won’t guarantee you have no air bubbles in your mold but it will significantly reduce the chance of it happening.

So take a deep breath, load up your brush with mixed RTV and start painting it over your masters. You’ll need a good stiff brush (hence hog’s bristle) because RTV is a very thick liquid. You should have ample time to carefully paint each and every master in your pour box before the RTV is anywhere near the end of its working period. But check your RTV MDS to be sure!

Once you’re done, put the brush aside in a cleaning fluid. RTV cleans up in painter’s turpentine and make sure you come back and thoroughly clean this brush once your mold is fully poured. It’s a little ironic while working up this tutorial I was so busy taking photos I completely forgot about the brush I’d used until the next morning. A brush loaded with set RTV is a throw away. This is also why I use cheap hog bristle brushes for all my RTV and plaster casting work, because you can throw them away! I buy a pack of 10 various brushes from a local ‘$2 shop’ regularly.

9. Filling the mold with RTV.

Finally, take your remaining RTV and slowly pour it into the box to fill your mold. I generally try to pour in at a corner or edge and let the thick RTV ‘roll’ across the masters to cover them completely. I believe this should introduce less bubbles than say sluicing RTV all over the mold.

Another tip with pouring is make sure the rim of your mixing pot is clean. You’ve just mixed the rubber and hardener in there and there may be some unmixed components around the rim of the pot which you do not want to pour into your mold.

While pouring you may notice there’s a little colour variation in the RTV as it goes in. Usually this is obvious because you can see the ‘ribbon’ of RTV you’ve just poured laying on to of the RTV already in the box. Don’t worry about this too much unless it’s very clear you have unmixed rubber at the bottom of the pot. If so take a moment to regret not completely mixing the components before pouring. Then stop pouring and try gently stirring up the RTV in the mold with a brush or tool to mix it in with the rest. You can also try to recover the partially mixed rubber left in the pot by adding a little more hardener.

It’s also worth noting that RTV is ’self adhering’ which means you can later pour additional RTV into a box partially filled with set RTV - providing the set RTV is reasonably clean and free from dust etc. I wouldn’t recommend it but you can use this to recover botched pours where something has gone wrong with your mixed RTV halfway through.

10. Leaving the mold to set.

And you’re done! Stand back and admire your handiwork for a few minutes. Pay particular attention to the edges and seams of your pour box because if you notice RTV escaping anywhere you’ll have to deal with it now. The truely paranoid might light to keep a blob of Klean Klay handy just in case they need to shore up any gaps or holes. This hasn’t happened to me yet but you never know…

Make sure the mold is placed somewhere level and out of the way to set. Level is very important because eventually you want to turn this mold over and pour resin or plaster into it which means the bottom has got to be flat and level. Out of the way because there’s normally a long setting time involved. Again check your RTV’s MDS for details. Then wait at least twice as long as that before you go back to it.

Seriously, I usually pour in the evenings and wait 24 hours for a product with an 8 hour recommended setting time. Do not be tempted to mess with your mold until you’re sure it’s set. RTV is a deceptive product - the surface can appear set while the interior (next to your masters) is still goey. Imagine your surprise at discovering that while trying to peel the mold off! Yes I speak from bitter experience.

There are three techniques I use to avoid this issue:

1. The first I’ve already mentioned - be patient!
2. The second is to keep the mixing pot next to your setting mold as in the photo. The pot will likely contain some dregs of RTV from your pour. You can examine these dregs to see how set the poured RTV is likely to be.
3. The third I like to call the ’spring test’. Come back to your mold later, when you suspect it may be set. If the surface looks set and the dregs in the mixing pot are fully set take a blunt tool (eg. paintbrush handle) and give the mold surface a good robust prod and hold the tool there. Then suddenly pull it away. If the RTV quickly springs back to a flat surface it’s likely the interior is well set too. If the RTV exhibits any reluctance to return to a flat surface, with the indent you made slowly fading away then for goodness sake walk away because the interior is not fully set.

I realise this last test is quite subjective but believe me it works. Cast a handful of molds and you’ll likely see at least one that does this when you expect it should be completely set. Be patient and give it another day of curing time. If you’ve mixed the RTV well enough that at least the surface has set then eventually the interior should set too.

If you finally give up and peel the mold away from the masters only to discover some or all of the interior has failed to set then it’s likely that your rubber has been contaminated or has aged (consider throwing the batch away) or you constructed your masters from some material that retards the RTV setting process. This is unfortunate. As I mentioned in the previous post sulphur containing plasticene can have this effect, but that’s the only mastering material I know to avoid. There may be others - I use a lot of DIY products, epoxy putties including green stuff, resin pieces and plasticard for my masters without difficulty.

In the next post where we reveal the final mold!

At the moment I’m pouring molds of various sizes for several projects and thought it would be a good opportunity to put a tutorial together for reference. Particularly since several visitors have asked me about mold making in the past.

This tutorial focusses on ‘garage’ one sided mold making with off-the-shelf RTV and casting with resin/plaster products. Using one-sided molds you can create spectacular terrain and modelling details to improve your gaming table.

Two sided molding is possible with these techniques but I find the results are often disappointing. For high-detail two sided molding you really need professional and expensive pressure vulcanisers and spin casters imho.

I learned mold making simply through Googling the web and trial and error. Hopefully this tutorial will save you some expensive mistakes and be at least as useful as others already out there.

As I live in New Zealand the mold making products I use are fairly specific to the Australian market. My materials are all supplied by TopMark in Auckland who are excellent to deal with if you happen to be a NZ mold maker.

For our US visitors I’d recommend checking out the Hirst Arts site mold making page and/or related forums for US product suggestions.

Create Your Masters

The first step to creating a mold is having something you want to copy in plaster or resin. You should expend a considerable amount of time creating your masters and you should aim to make them as sturdy and as highly detailed as you can.

Make them sturdy because it’s always nice to keep your masters after molding them for future modification and possible remolding. Molds created with most RTV products do not have an infinite life so being able to create additional molds from your master can definitely be useful. Particularly if you’re a hobbyist seller like myself. In fact the pieces I’m molding here have already been remolded several times.

Make them highly detailed because once you have successfully created a mold you can easily reproduce them, producing tens or hundreds of casts with ease (and a little time). So it’s worth applying all your modelling skills and equipment in the creation of a master worthy of molding.

A final word on masters: Copyright applies to all original works. It’s illegal to copy and sell work derived from other individuals/companies without their explicit contractual permission. Don’t do it. Create your own masters. Take it from me it’s infinitely more satisfying molding your own work.

Making the Mold Pour Box

1. Assemble the materials for your mold pour box.

The pour box is a watertight container that holds the RTV around your masters while it sets. I build all my pour boxes from 3mm MDF, foam card offcuts, masking tape and Klean Klay modelling clay.

MDF (medium density fibreboard) is a pressed wood product with a fine grain. I use 3mm MDF for most of my terrain basing so have a lot of smaller offcuts left which I use for forming the base of the pour box.

MDF is good for the base because it’s stiff and flat. The base will form the open face of the final mold so I want it as flat as possible as I use a ’smooth cover’ technique of casting. This is where a flat piece of plastic or glass is laid over a poured mold to ensure the cast pieces have flat bottoms.

2. Arrange your masters for molding.

RTV is expensive so you want to arrange your masters with minimal wasted space. However you also need to leave at least 4-5mm (or 1/6th of an inch) between each piece inside the mold and a little more for the external walls, say 5-6mm. Set RTV is quite flexible, so you need relatively thick internal and external walls to ensure your cast pieces aren’t deformed by the walls bowing when you pour resin or plaster into the mold.

Obviously the best thickness to use varies depending on the set strength of the RTV product you’re using and these estimates may be a little generous. I notice molds from professionals like Bruce Hirst have 2-4mm internal mold walls.

Once you’re happy with the arrangement glue each master down with a small dab of superglue. It’s important the masters are firmly fixed to the MDF base. RTV is a dense liquid, so light masters can float up before the mold sets which in the worst case can leave you with a solid block of RTV you’ll have to cut your masters out of!

If you ever want to remold or modify your masters chances are you’ll want to get them off the base. A small dab of superglue can be broken by twisting the master off the MDF. However if you’re confident you won’t rework the masters then definitely glue them down solidly because it won’t hurt.

3. Assemble the pour box.

Foam card is ideal for this because it’s breakable foam sandwiched between two layers of thin card. You can cut through one layer of card and some of the foam while leaving the other layer of card intact and then fold it to form watertight corners.

Take a continuous strip of foam card that’s long enough to entirely surround your masters. Stand it on the base and cut the outer side (from the centre) of the foam card and fold it in towards the masters, so the intact layer of card forms a watertight inner corner. Rinse and repeat for as many corners as you need.

Don’t feel obliged to make square or rectangular pour boxes. Many of my molds are irregular shapes simply to avoid wasting Ultrasil filling empty corners. The only important thing is there should be sufficient space between your masters and the foam card so the RTV will form a decent external mold wall.

Once you’ve cut the foam card into a shape you’re happy with, tape it down to the MDF using strips of masking tape around the outside of the box. I usually also tape the final edge of the foam wall shut too.

Enough masking tape would probably be sufficient to stop the RTV from escaping from the pour box but it’s pretty viscous stuff and can flow out or under the smallest gap. For this reason I also run a bead of Klean Klay around the entire pour box, making doubly sure the edge of the foam card wall is nicely sealed down to the MDF base and the final open edge is completely sealed.

Klean Klay is a reuseable modelling clay for use with RTV molding. Normal plasticene and some other modelling clays contains sulphur which will stop any RTV that contacts it from curing properly. This is a bad thing. You can also create temporary masters from Klean Klay, as well as use it for sealing off half of a master for two sided molding, so it’s handy stuff to have around. It’s pretty cheap too and you should be able to pick it up from any supplier that also stocks RTV molding kits.

Right! That’s your pour box made, next comes estimating the amount of RTV you need and pouring the mold. This is covered in the following post…

The Painting Clinic (a good site in itself) has an excellent tank weathering tutorial for Flames of War tank painters.

I have an entire 1500pts German DAK army to paint that’s currently living in a shoebox in my garage, so might try adapting some of these techniques to a desert scheme.

As an aside regular visitors may notice I’ve been posting more links and less of my own work recently. I’ve got plenty of projects on the go, but nothing that’s reached a point that’s worth posting imho! Next week I hope to be revealing some nifty projects.

Ok, so this isn’t really related to 15-28mm scale wargaming, but you can’t help admire the steady hands and fine technique of these traditional pin stripers (YouTube video).

Interesting looking brushes they’re using too, horsehair or some kind of nylon? Whatever they are they’ve got mighty long bristles. Ah, apparently they’re a blend of natural and artificial fibers.

Via Boing Boing.

This rather dark night time photo represents the first set of resin casts from a mold I made the night before. It’s a set of 15mm scale window frames designed to be pushed through 5mm foam card.

They are a little over scale for 15mm but if I made them to scale I wouldn’t be able to cast them. They will form the basis of a larger project I’m working, inspired by Johnathan, a fellow Flames of War gamer.

Now I just have to cast 5-6 sets for the next stage!