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A question regarding straightening a warped plasticard roof


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Hi all,

I've a scratch built roof for a diesel depot I've been building that has warped. All four corners have curled upwards. I've done a search and seen other people have attempted to correct similar issues on their models and I know it is possible to cure with hot water and the plasticard clamped to a straight edge but I would just like some clarification from those who have attempted it as regards a few points.

* How hot should the water be? Boiling? Very hot? Cup of tea hot? Cooler than that?
* How long should I immerse it for?
* Should I quench it or let it cool naturally?

Thanks for your time. P.E.

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Hi PE.

 

Your roof probably warped due to a lack of sufficient bracing and Plastic,once it warps,stayes warped as when it's wrapped around a bottle to form a cylinder where it's immersed in hot water - not boiling - then after it has been allowed to cool down, or immersed in cold water until it has, it will then hold its shape unlike carboard say as it tries to spring back so, gentle heat treatment would be the answer and you could try pinning or taping the roof down then playing a hair dryer over the effected area then allowing it to cool before you unpin it.

 

However, Peter Leyland might have a better solution than this as he works in styrene all the time and I doubt that there's very little or nothing that he does'nt know about working in this material.

 

Cheers.

Allan

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How long did it take to make? You could spend lots of time trying to correct the fault when that time could be spent re doing. It. I have suffered the similar problem and remedied it with additional bracing but my eye always got drawn to the roof and I knew it was not right and in the end it was replaced. Adequate bracing and use a thicker plastikard that does not sag with visible edges being beveled will help.

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Yes it took a good while with skylights and scratch built guttering. I'm going to attempt to strengthen it first with another layer of plasticard. It's one sheet of 40 thou with thin plasticard corrugated sheet applied on top. if I apply a second sheet of 40 thou hopefully that may achieve the desired effect. I'll be gutted if I have to start again.  

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Yeap, could work on the principle that 2 ply plywood does not work but three ply does! I think the thin ply will be trying to lift and pull against the 40 thou. In the corners and middle of the roof so if there is room to make a socket out of square or round tube. Then attach plugs to the same locations on the walls of the buildings and that will give you firm fixing points, evergreen stock would work

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Hi,

with regard to the ply principle, unfortunately I have found that it doesn't work with plastic, the reason is plywood has a grain that you can see, so you can alter the line of grain on each piece to make the ply become effective.

The trouble is with Plastic, it too has a grain of sorts but unfortunately not seen by eye so therefore you can't determine which way to lay it, that is why I am not comfortable with laminating plastic for the sake of bracing or strengthening a wall section etc.

It is difficult to give advice in this case as not seeing how you have constructed the roof section, do you have a photo to look at?

 

cheers

Peter A L

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I've used hot water baths to bend plastic sheets and the temperature I use is (from your range) between cup of tea and boiling. Also, you must hold the plastic in the water vertically with pliers because if it settles on the bottom of your pan, it curls into a funny shape and is ruined. I didn't time it but I'd guess each sheet was in for 2-3 minutes, then removed and bent round a glass former, string applied, then reimmersed for another 2-3 minutes, repeated if necessary. I let the plastic cool naturally. As Allan says, it retains its form. 

 

I've only ever used single sheets (Wills or 60-80 thou plain) - I don't know how a double thickness would react but I'd be very wary. 

 

As Peter suggests, a photo could be useful. 

 

 

Edit:

 

http://www.rmweb.co.uk/community/index.php?/topic/75194-modelling-a-castle/ - one of my experiments with Wills sheets. 

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I'm trying to make it so that the roof is removable for track cleaning and general viewing. It's based on a prototype so I don't have any leeway to play with either. I shall be sure to update you all on my success or failure.

Then I would have a go at a plug and socket use evergreen tubing as different sizes nest inside each other

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Hi,

with regard to the ply principle, unfortunately I have found that it doesn't work with plastic, the reason is plywood has a grain that you can see, so you can alter the line of grain on each piece to make the ply become effective.

The trouble is with Plastic, it too has a grain of sorts but unfortunately not seen by eye so therefore you can't determine which way to lay it, that is why I am not comfortable with laminating plastic for the sake of bracing or strengthening a wall section etc.

It is difficult to give advice in this case as not seeing how you have constructed the roof section, do you have a photo to look at?

 

cheers

Peter A L

I have found it useful when using a thin outer layer as the glue does seem to want to pull the other layers. I know that some modellers suggest drilling holes into the other layers and then glueing the top layer through the hole thus reducing the effect of the glue on the layers

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Hi,

It is more than possible to glue another piece of plastic to another by the use of Liquid Poly, you can be quite generous with this by applying to both sides then pressing together but never 'in my experience' for the benefit of strength but only to enable an overhang section of roof on top of the roof piece proper.

I have attached a photo showing how I go about creating a strong roof bond, via roof trussing, albeit wood trussing or steel as in a Diesel depot for example.

 

cheers

peter

 

post-1241-0-99308400-1413407636_thumb.jpg

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If you use solvent glues over large areas it will play havoc with laminations as will Evostik contact adhesive but superglue doesn't soften the plastic as the former two glues do and, in fact, strengthens it as it forms a thin rock hard layer after it sets which of course is instantly.

 

I have superglued Slaters thin corrugated sheeting over 2mm cardboard with great succes using high viscosity superglue but once, when I used Evostik instead, it 'curled' the roof wherever it could but only after a few weeks where it seems that the glue never stops fighting for superiority - and wins.

 

However, I would say that covering large expanses with 40 though styrene would require some very serious bracing as that suggested on here by the experts ane really you should be looking at 80thou minimum and, even then, it would still need substantial bracing.

 

Also while I think about it, has anyone ever considered 2mm clear acrylic  sheets that's used for secondary glazing etc from wicks as a sub base then paint it after to disguise it ?

 

Well it certainly won't warp as I've used it on Gauge 1 glazed station canopies - 16 foot of it actually -  so it might  well be worth a try...

 

Pictures available if you want.

 

Cheers.

Allan.

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Hi Alan,

yes, re clear acrylic sheets are what I use for larger roofs as on say a diesel depot and just paint it matt black on the under side :-), I buy it in 6ft x 3ft sheets for a pittance.

I'm quite cunning too with fixing roofs, as I have the outer layer for the covering with slates ( Paper ) and also underneath the roof top layer is fixed with extra layers so it pulls against itself, so nowhere to go :-)

the photo does not show this at that stage of the build process, only the trussing.

cheers 

Peter

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Hi Alan,

yes, re clear acrylic sheets are what I use for larger roofs as on say a diesel depot and just paint it matt black on the under side :-), I buy it in 6ft x 3ft sheets for a pittance.

Peter

 

Yes Peter, it's certainly a hell of a lot cheaper than the clear glazing that you get in model shops and I use it now for everything from cottages to canopies and signal boxes in particular.

 

Cheers.

Allan

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Hi Alan,

yes, re clear acrylic sheets are what I use for larger roofs as on say a diesel depot and just paint it matt black on the under side :-), I buy it in 6ft x 3ft sheets for a pittance.

I'm quite cunning too with fixing roofs, as I have the outer layer for the covering with slates ( Paper ) and also underneath the roof top layer is fixed with extra layers so it pulls against itself, so nowhere to go :-)

the photo does not show this at that stage of the build process, only the trussing.

cheers 

Peter

 

Hi peter do you have any further pics showing updates to the engine shed roof you've been constructing?

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I have had the same issue with a number of my roofs, I tried to brace after the warpage had settled, but it just pulled away from the bracing.

 

I tried to just build it simple as possible and manually bend back in to place. But as all the tiles were individual it pulled the paint away from the joins and you could see the white plasticard between the joins.

 

In some places the warpage has affected the model with good results as a real roof isn’t flat and has many waves across it, my biggest issue is on the corners. Like most I have made the roofs removable so I can rebuild if required.

 

For myself I have just put up with it and done what I can to rectify the issue. It’s just demoralising when you have spent hours/days/month on a building to see it curl like a hair!

 

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A substantial substructure is every bit as important as the outside structure of a building and particulary one with a large expanse of walls and roofing - one can never install too many wall/roof supports - and try and employ the  thickest material logically possible and, as Peter has agreed, 2mm thick acrylic clear sheeting makes for a really good warp free foundation.

 

I once built a very large Gauge One four road engine shed out of 12mm MDF and it took two to lift it ! Somewhere I have a picture of it...

 

Cheers

Allan.

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Hi Baz,

yes, as you say very demoralising, after spending so much time creating your building.

I have found that the least stress on a roof, the better, nowadays I use paper for my slates instead of cut plastic or preformed plastic as the later types tend to pull the roof layer away when the glue sets.

If I construct the roof piece from plastic, I fix a layer of cartridge paper to the plastic with liquid poly and will have no effect on the roof, then once full dry, I will fix the paper slates to the cartridge paper with school glue PVA, once that has had time to dry, I will then paint the slates semidry/wet twice with enamel paint, then dry brush to weather up, no stress on the roof to make it pull away.

One thing to remember, what you glue/fix to the roof surface should never be greater than how you fix the roof proper.

The slates are made from a grid pattern on the computer and printed out and cut as two layer with a sharp scalpel then with a blunt scalpel cut into the first run lines then lay onto the roof  as mentioned above.

cheers

Peter

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