Tuesday, 24 July 2012

Flat Out

So what do you reckon this basket of groceries is all about, then?...

I wouldn't have blamed the checkout operator if she gave me a few strange looks when I walked up with a jumbo roll of sellotape, cling film, furniture polish, cocktail sticks and a jar of Vaseline. Was I some kind of fetishist?

No. Just a slightly frustrated modeller trying everything he can think of in an attempt to get smooth, flat backs on his resin casts.

It's sometimes the case when using an open mould, as I am, that the top surface of the resin does not set completely flat but with a slight hump. I tried to improve matters by passing a flat edge along the top surface after it had been poured which helps a little, but you do get a bit of a bow wave effect which leaves the casting deeper at one end than the other.

So I consulted some of the village elders to see what they had to say. They all suggested placing something flat on top of the mould as the resin set. (It doesn't need to be exposed to the air, of course.) The difficult bit is how to stop the resin becoming stuck to whatever you put on top of it.

Suggestion one was a piece of clear plastic sprayed with cheap furniture polish, the cheaper the better.

Didn't work!

In fact, as Himself would say, it stuck like sugar to a blanket. (Perhaps something to do with the type of plastic I was using?)

Suggestion two was to wrap the plastic in cling film.

Not entirely successful.

The resin certainly doesn't stick to the cling film, but try as I might I couldn't get a flawless cling of film. When the resin was set the back of the cast was as rippled as a beach with the tide out.

I tried the polish again, but this time on glass.

Just as bad! In fact I had to chip the resin off the glass fragment by fragment.

By this time I was more than a little fed up. In fact I was rather grumpy and beginning to consider whether this resin casting lark was worth it?

I spent a few days after that in an exhaustive trawl of search engines to see if I could find anyone using any other methods.

I noticed how some people who do split mould castings mentioned using Vaseline as a cheaper alternative to expensive mould release sprays to keep the two halves from sticking to each other. And thinking more about my tribulations with cling film I also wondered whether there was any chance of using sellotape? I knew I would have half a chance of applying that to the plastic with no imperfections. The big question was would the resin stuck.

I experimented with both on an off cut of plastic. I covered one half with sellotape and smeared Vaseline on the other side before dropping on two small blobs of resin.

Success! The set resin popped off them both without a fuss.

I decided that sellotape would be the simplest and less messy solution to try first and went out and bought a roll of clear parcel tape. So far I have managed to cast four wagon sides with backs that are billiard table smooth.

I hesitate to declare that I've got this sorted once and for all because resin casting seems to have a habit of biting you on the bum whenever you drop your guard and dare to think you're the master of it, but just now the kit production prospects are looking a lot more positive than they were last week.


  1. It is common practise to use a sheet of glass on the open side of the one piece mould.


  2. I've had good luck using the 0.015" thick clear sheet material sold on the Evergreen Styrene rack. It's not styrene, but something else. I spray the material with silicone mold release, and resin won't stick to it.

    I "unroll" the sheet onto an overfilled mold (eliminates the possibility of trapped air), then place a sheet of window glass over the non-stick plastic, then place weights on the glass. This regularly results in a super flat resin casting, with ultra-thin flash on the open face of the part.

    It's not the only way to do it for sure, but it works well...