Which plaster is best to use on top of foam insulation board?

[Douglas G]

Having created my landscape using Knauf pink insulation foam, I am moving to the surface.

 

I am planning to use the sort of dishcloth material sold on a roll for washing cars, to be stuck on to the foam surface with PVA (as In Stephen Williams' GWR Modelling book), and then topped with a coat of plaster or filler with brown acrylic paint added. I would also include some PVA with water in the mix for flexibility.

 

I was wondering if people can recommend which type of plaster should give best results in terms of strength, flexibility and lightness.

 

I have identified the following as easily available (most are powders rather than ready mixed):

 

Polyfilla Multipurpose Filler

Artex Easifix Multi Purpose Filler

Wickes All Purpose Interior Filler

Wickes Quick Setting Patching Plaster

Wickes Ready Mixed Textured Coating

Artex Textured Finish powder

Gedeo Light Plaster (Hobbycraft)

 

I think ready mixed products tend to be more expensive, and make it harder to mix in brown paint. I wonder if Artex would be more flexible and resistant to cracking than plasters or fillers?

 

Any advice gratefully received!

[ThaneofFife]

Thistle do a Bonding plaster (blue/purple bags) that you can buy in Wickes - great for a rough looking finish (think of it like the orange juice you can buy - "with bits"     this is normally used to patch up deep sections of wall/holes etc  or as a backing undercoat plaster (instead of using multi finish or board finish onto board) so if you have thick/heavy hollows to load up with plaster either pack out with balls of paper then your cloth then one of the finish plasters or just gob on the Bonding coat stuff.  this will be much heavier than the former method.

Use the multi finish if youre looking to get something fairly smooth.

strength wise the proper plasters (not the fillers) are pretty strong/durable.

 

if you have lots to model then buy a big 25kg bag for about £7 but look through the pallet to get one with the longest "shelf/use by date" as most of the proper plasters are dated and go off after about 3 months although thats not as important for railway modelling as you dont really want the sort of perfect flat smooth finish like youd expect  on the walls and ceilings in your home. after so long the bags go hard.  try to keep yours indoors in a dry place and off the floor.

 

for top coats that you just want to paint allow the plaster to dry naturally - close all windows and doors to stop draughts and turn the heating right down to avoid cracking.  allow a good few days then it turn pink/light brown.

 

old credit cards or free health lotto cards are great for basic forming and smoothing.........

 

you can experiment with the mini-bags of plasters too but they arent very cost effective.

[buffalo]

Having gone to the effort of building a lightweight board using foam, I wouldn't want to put all the lost weight back by using plaster. Instead, I've use Sculptamold directly on top of the foam. It's very light and equally easy to use, though rather more expensive than plaster. For the results, see my blog entries here and here.

 

Nick

 

 

[daftbovine]

I used Polyfilla multipurpose filler to fill in any gaps and then sanded the surface with sandpaper. I then used a coat of water based paint followed by the usual scatter materials. Unless your layout is for exhibition purposes, how strong does the scenery need to be?

 

I think that sometimes we over engineer our layouts, if they are for home use, they won't get flung about will they?

[roundhouse]

I use any own brand such as Wickes or Homebase interior fillaer

 

I put it straight onto the foam. I do add a bit of black or  brown water based paint to hide any obvious knocks so it doesn't show bright white.

 

If adding filler near a joint a also add a bit of PVA .

 

Ian

[Mike Bellamy]

Having gone to the effort of building a lightweight board using foam, I wouldn't want to put all the lost weight back by using plaster. Instead, I've use Sculptamold directly on top of the foam. It's very light and equally easy to use, though rather more expensive than plaster. For the results, see my blog entries here and here.

 

Nick

Not used it myself but I have heard good reports about Sculptamold as it's light and sets hard. Some years ago, a demonstrator at the Derby show had a rock face he had made with it and every time someone asked about it, he banged it on the table to show how strong it was - of course by the end of a busy two day show, it had started to crack but had proved the point. One person watching that demo was Paul Martin (EDM Models) and he now sells the stuff as shown here

http://www.ngtrains.com/Pages/Scenic/sculptamold.htm

 

 

Mike

[buffalo]

Not used it myself but I have heard good reports about Sculptamold as it's light and sets hard. Some years ago, a demonstrator at the Derby show had a rock face he had made with it and every time someone asked about it, he banged it on the table to show how strong it was...

 

Talking of rock faces, this is also Sculptamold shaped with a plasterer's leaf and painted. In this case, it is on a an expanded, not extruded, polystyrene base. Again, very light weight.

 

 

Nick

[peter220950]

As you note Artex has a bit of flexibility, which reduces the risk of cracking, or you could try Gyproc Joint filler or cove adhesive, which are similar, they are finer than than traditional plasters like browning and finish and should therefore be more suitable for use with bandage type materials.

 

We have been using the same bag on the club layout for many years, and it seems to be suitable for a hard shell finish on Styrofoam, without suffering damage in transit.

 

PVA and poster paint in the water pre-colours the mix in case of chipping.

[ozzyo]

What's up with plaster of Paris?

[Douglas G]

Thanks everyone for you helpful advice.

 

Lots of food for thought. Sculptamold and Gyproc joint filler sound particularly useful.

 

I do have a pack of Javis Scenery Maker plaster impregnated scrim to try as an alternative on embankments and will report back on how it works.

 

I appreciate the comment about over-engineering. At the same time, the scenery is such a fundamental thing that it if starts to crack or come loose, it is a massive job to put it right. So I really want to get it right.

 

Cheers,

 

Douglas

[Doughnut]

I use Wickes One Coat (powder in the blue bag)  Fairly cheap and does the job well.

 

Dave

[Douglas G]

Having tried the Javis Scenery Maker plaster bandage, I have found it has worked well for my purposes. I stuck the bandage down dry onto the styrene with PVA and then brushed on water with some brown acrylic paint added, working the plaster once liquid to fill the holes in the scrim. I have found that a single layer with no overlaps gives a good hard shell without adding much weight. It just needs filing at the joins and any imperfections with a thin layer of Polyfilla.It won't actually cost that much to do the landscape with the Javis product as a lot of the area is track and tarmac surface and I think only three or four rolls will be required for the grass areas.

 

Thanks again to all who contributed ideas and suggestions.

[Kris]

I use sculptamold. Very very light weight compared to plaster. The finish is not as fine however so if you're looking for something ultra smooth this is not the product you want.