Is it me or has anyone else noticed that plaster bandage takes forever to dry if laid over a polystyrene core ?

I'm going to kick the polystyrene into touch and use either wire netting or crumpled newspaper for the landform.

It's pretty hot out here but I've already waited nearly 3 days for the plaster to dry out and it's still damp - ish !!!  My feeling is that it needs circulating air to dry effectively and polystyrene just doesn't offer that.  It seems to trap the moisture in it.

Any similar experiences out there ?

I will let you know Peter after I try my plaster method though I have seen it done in front of my eyes on at least two exhibition layouts.

[user=95]Sol[/user] wrote:

. . . though I have seen it done in front of my eyes on at least two exhibition layouts.

I remember seeing Sol walking around an exhibition with plaster in front of his eyes - bumping into people . . . 

I used Chux Super Wipes with casting plaster - otherwise known as plaster of Paris.

Don't buy any plaster, Sol.  I've still got 20 kg of the stuff.  It helps having a daughter at Bunnings!  ;-)

OK, a couple of Kgs then if you are going to next NMRA meet July 24th or DECCA meet at my place on the 25th.
I stll have a bit I can try.

Peter, it sounds to me your plaster is past it`s use by date ??
plaster of paris/modelling  goes hard in minutes, finishing plaster about 30 mins,
if yours is still wet after two three days it is U/S mate chuck it and get some new stuff.

lol::cool:

It is new stuff Owen - Jarvis I think - bought on my last visit to UK by car in February.

I'll try a piece "on it's own" to see how quickly it sets.  I've experienced this problem before when using that gap-filling expanding foam as the land-form and thought it might be because the air can't circulate all around.

Whatever the reason, it's most annoying !!!

I agree with Owen whenever i have used it the peco or gaugemaster stuff holds shape and is pretty dry within 30 minutes Peter

Pinch Liz`s hairdryer

Brian

What do you guys use for the land-form under the bandage ?  I think I remember using it years ago over chicken wire with no problems - that's why I'm wondering about the effect the foam is having (if any).

I note Rick used newspaper which would help to absorb some of the moisture.  My thoughts are that because the foam is waterproof, all the drying out would have to take place from one side only.  Maybe I should try with less water around although I'm only dipping it for a few seconds as it is. :???::???:  I do think that, like all things today, they've "economised" on the plaster content - I'd have preferred more to help fill the weave of the bandage.

Peter, I have used flywire which is about an 1/8th square mesh, in either a fine metal or fibreglass  & plaster straight over it. Flywire is used on screen doors & windows. I would have used that if I was not given all the foam.

Peter, I must agree the last time I used bought plaster bandage it was a lacking plaster content,
since then I mix my own and use any old cloth with it.
let us know how the test piece turns out.

lol::cool:

Never tried plaster bandage, but I have noticed PVA glue seems to take ages to dry on when used on polystyrene.

I have used plaster over foam, and I believe it takes longer to dry, even on my semi-outdoors layout.
 As for plaster cloths/bandages I like to make my own with Chux cloths, paper towels or lint.

Mike

I think Chux cloths are, as Brian said, what are called "J Cloths" in UK.  Apparently, they don't exist in France - at least Liz says she's never seen them.  I might try some cotton cloth or even paper towels.  I seem to remember John Dew used paper towels on an embankment.  I do have chicken wire but it's not very small mesh but worth a try.

Hi Peter,

I used some ModRoc type bandage from Squires on polystyrene for Kernow Junction this year. It was a new batch and like you it took a while to dry but hours rather than days- even outside when it was sunny. I had dipped it into a mix of water with some PVA added and I suspect it was the PVA that was holding up the drying process. However I used a bit on Devon Junction over chicken wire and it dried much more quickly. It could be the amount of water either that the bandage was holding or the lack of air getting to the other side of the bandage on the polystyrene model.

In both cases however when I added a bit of extra plaster (Yeso a.k.a. plaster of paris) mixed with a little PVA, this layer took days to dry on both layouts. Wierd.:hmm

Les

Temperature does affect the speed with which plaster will go off but so will humidity.  It will go off much faster in dry air simply because the moisture has somewhere to go.  

That said it still should not take three days in reasonable conditions.  My latest little patch went off in two days outdoors in very damp weather.  That was laid over mushroomed newspaper as usual.  

I have a few small areas where polystyrene is included in the substrate but isn't the major part of it.  The steep slopes of the sand dune scene include some scrap polystyrene pieces but the basis is still newspaper and the plaster sits almost entirely on that.  It went off in the usual day or two.

Nearly all types of plaster age can affect it curing times.

for example Thistle board plaster you always tried to get as new as possible bags as the older it is the quicker it goes off.
Wheres as the the old browning plaster the reverse was true if new took ages to go off so older bags were preferable.

Brian

Just another aspect on the plaster situation.
As a spark we used to come up against breeze blocks ,where when one tried to  cut out a neat square recces to take a switch or socket box one ended up with a ragged hole according to how the material broke away . So we used" casting plaster" spreading it into the hole and pushing the metal box in to the soggy mass
. The casting plaster went off in a matter of minutes,provided a firm fixing ,and enabled us to get on with the work.
"Casting plaster "came as coarse ,medium, and fine .  this was used by conractors on site to cast ornate cornice work and similar fine work. In stately homes and theatres and  other buildings of that type where a faithful reproduction of a particular sample piece was required  Now the point is we got used to this material and found that it had slighlty different properties to ordinary plaster of paris . It had a particular fibrous content which enabled  to one to sculpt the finish up to about 15 minutes before it suddenly became unworkable.  So then if you can locate a fibrous plaster works (yellow pages ) and get hold of a bag !cwt of this product it will if properly stored last for years and is invaluable as a modelling aid . As a landcscape  filler ,or  press baco foil into it for rock faces etc.  .Make it up as a creamy texture pour or apply with a putty knife.goes off in minutes so work fast. can be shaped for roads or similar. Will take paint ,but is not weatherproof so no good for outside. Coming to Petermacs problem i can only think that whilst it has been obtained recently it had "gone off" usually when it is mixed if it has a grainy look and feel then it has been stored in damp conditions. If it had been in good condition it would not take that long to go off. Happy to bring some down to Cambourne for you Petermac ,but you may be over the problem by then.

Thanks for all your comments and advice guys. :cheers

Today, I tried some of the same bandage over chicken wire - it worked perfectly !!!  Dried in less than 30 minutes and then I sprinkled some casting plaster on top, sprayed it with water and worked it into the bandage weave.  I'm happy with the results.  

Some I laid yesterday over polystyrene is still "soft" so I'm assuming it is the fact that air can't get behind it with the solid substrate.  It's pretty hot here although the last couple of days have also been humid but the wire says it all !!

Regarding the type of plaster - around 15 years ago, I went to a builders merchant in London to buy some Carlite Browning.  He asked if I came from "up north" because they hadn't used browning in London for years - plasterboard and board finish only !!!

If you ask any "handyman / builder" here (the English type) they'll tell you that french plaster is impossible to use !!!  It's a real pig and sets in minutes - suddenly !!!  One minute you've got a nice "soft butter" consistency and 2 seconds later, you've got concrete.

I've got some casting plaster - used it for Linka mouldings.  It's not fibrous although you can buy bags of "fibre" to mix in but it's too coarse for "00" gauge mouldings.  I'm going to experiment with other grades of plaster to see if I can find one that gives me enough time to work with it before it sets hard.  I'm sick of washing / chipping out bowls of hard plaster. :twisted::twisted::twisted:

I'll have to find something because that bandage works out at a fair old price !!!!!

Peter
If you pop to the french equivalant of B & Q you should find some plasterboard or dry wall adhesive.
that mixes as thin as you want and sticks like Sh*t to a blanket and is cheap aswell.

B&Q | DIY Products at Everyday Low Prices | DIY at B&Q


Brian