Working with DAS

[figworthy]

I've been doing a bit of fiddling around with DAS.  I've used it to created a cobbled area between tracks, and that seems to work OK, but I'm having problems when I try to use it on a lump of styrene prior to mounting it (walls, bridge abutments etc.).

 

I cut a lump of 40 thou styrene to size (and in the last case I braced the back of it using 40x100 thou plastruct).  I then roughened and PVAed the business side of it before applying a thin coat of DAS, with a view to scribing it later.  When I came back the following day, I found that the whole thing had taken a gentle curve (DAS on the inside).  The bracing was still rigidly attached, it had curved as well.

 

How do I stop this happening ?

 

 

Adrian

[allan downes]

Well Adrien, the best man to answer this would be Iain C Robinson, the master of anything to do do with Daz, but I would have thought that with  PVA being a water based glue, it wouldn't adhere sufficiently enough to plasic - card or ply yes - and this is what  I used to use when modelling with Pyruma Fire Cement which in effect, is much the same thing. 

 

Cheers.

Allan.

[Mike Bellamy]

David Wright uses DAS for both buildings and things like yard surfaces etc. He has written articles in most of the monthly magazines and has also produced a video and book showing the techniques used.

 

DVD http://www.dovedalemodels.co.uk/model-making-dvd/

 

Book http://www.dovedalemodels.co.uk/making-rural-buildings-for-model-railways/

[HLT 0109]

I have had some success using Das with styrene.  Initially, I simply pressed the Das on to the strip of styrene (without glue) and it has remained stuck.  I did however either encase the styrene entirely in the Das or ensure that it lapped over the edges.  I have also used it with PVA glue and found it entirely satisfactory.  I have not used the method for a complete wall but only for the capping.  I have not experienced any warping but I have always attached the capping while the Das was wet, scribing it in situ, also whilst wet.  As Allan suggests, the walls in question were made of old plywood but, as they were required to be curved, the wood was fixed in place first, then coated with the Das and scribed as before.  As long as they are stone walls, uneven scribing does not look out of place.

 

Giving a direct answer to your question - encasing the styrene completely in Das should prevent warping.

 

Harold.

[Campaman]

I would guess this is caused by the Das shrinking slightly as it dried, not sure how you can stop this apart from weighting it down somehow.

[figworthy]

I would guess this is caused by the Das shrinking slightly as it dried, not sure how you can stop this apart from weighting it down somehow.

 

To me that was the obvious reason, but I never assume that the obvious answer is the right one.

 

I had considered doing as you suggested, but I left it DAS side up to allow the DAS to dry.  I may have another go over the weekend and see what happens (I suspect cracking).

 

I was hoping to make up the sections, then scribe them, then fasten them into place as scribing some of the bits in place could vary between difficult and impossible.

 

I'll report back after the weekend.

 

Adrian

[figworthy]

Well Adrien, the best man to answer this would be Iain C Robinson, the master of anything to do do with Daz, but I would have thought that with  PVA being a water based glue, it wouldn't adhere sufficiently enough to plasic - card or ply yes - and this is what  I used to use when modelling with Pyruma Fire Cement which in effect, is much the same thing. 

 

Cheers.

Allan.

 

Thanks Allan,

 

Being a novice to this (and most other bits of this fascinating and occasionally frustrating hobby), I've tried several different approaches.  DAS straight onto sytrene didn't work as I couldn't get it to key.  PVA (leave to dry), then DAS wasn't an overwhelming success as I had problems with the PVA not sticking to the styrene, the final approach was to sand the styrene first, then PVA it.  This seems to allow the PVA to stick, and the DAS seems to bind to the PVA OK.

 

I'm using sytrene for two reasons I suppose, firstly it is relatively cheap and easily obtainable, and secondly, a lump of 40 thou sheet is plenty thick enough (so I thought) for a mounting surface, if I use ply then that is likely to be much thicker.  I do have some 2mm ply, so I might have a play with an offcut of that to see what happens.

 

 

Adrian

[Chubber]

Thanks Allan,

 

Being a novice to this (and most other bits of this fascinating and occasionally frustrating hobby), I've tried several different approaches.  DAS straight onto sytrene didn't work as I couldn't get it to key.  PVA (leave to dry), then DAS wasn't an overwhelming success as I had problems with the PVA not sticking to the styrene, the final approach was to sand the styrene first, then PVA it.  This seems to allow the PVA to stick, and the DAS seems to bind to the PVA OK.

 

I'm using sytrene for two reasons I suppose, firstly it is relatively cheap and easily obtainable, and secondly, a lump of 40 thou sheet is plenty thick enough (so I thought) for a mounting surface, if I use ply then that is likely to be much thicker.  I do have some 2mm ply, so I might have a play with an offcut of that to see what happens.

 

 

Adrian

 

 

I wonder if that smelly stuff, Copydex [?] might be the answer? It sticks to glass and the plastic that Tupperware is made from.......Having recently dropped an opened container of it on the kitchen work surface I am still suffering, i.e. 'Look! There's even some stuck to the xxxxxxx' over a week later. It didn't help that the cutlery drawer was also open at the time.....

 

Doug

 

 

PS As a serious aside for those of you with elderly/infirm family members, it does make rugs virtually non-slip by painting several wide stripes across the back and allowing to dry thoroughly. [Top Tip! Do not use a nylon bristled pastry brush for this job, it doesn't wash out......yes, another ticket to the dog-house.

 

 

D]

[The White Rabbit]

I've been doing a bit of fiddling around with DAS.  I've used it to created a cobbled area between tracks, and that seems to work OK, but I'm having problems when I try to use it on a lump of styrene prior to mounting it (walls, bridge abutments etc.).

 

I cut a lump of 40 thou styrene to size (and in the last case I braced the back of it using 40x100 thou plastruct).  I then roughened and PVAed the business side of it before applying a thin coat of DAS, with a view to scribing it later.  When I came back the following day, I found that the whole thing had taken a gentle curve (DAS on the inside).  The bracing was still rigidly attached, it had curved as well.

 

How do I stop this happening ?

 

 

Adrian

I had a similar problem when using DAS (and PVA) to model a small goods shed. The shell was balsa, braced with section several mm thick, but the drying DAS still produced a concave effect. I only applied it to the outside and sills and lips of windows and doors. This was in pre-RMWeb days and I got round the problem by cursing eloquently and with feeling and then using Wills plastic sheet material... 

[Chubber]

I had a similar problem when using DAS (and PVA) to model a small goods shed. The shell was balsa, braced with section several mm thick, but the drying DAS still produced a concave effect. I only applied it to the outside and sills and lips of windows and doors. This was in pre-RMWeb days and I got round the problem by cursing eloquently and with feeling and then using Wills plastic sheet material... 

 

My very limited experience with DAS has been identical, I tried the cobbly thing using a brass imprinter a la Downes and as it dried it pulled up the 2mm card substrate I  had PVA'd to the ply base. I really envy  some of the work I've seen on RMWeb but that experience has put me off. It certainly didn't let go of the card! Allan says he used to use Pyruma [sp?] fire cement before DAS but that gradually crumbled away......I know the feeling.

 

Doug

[HLT 0109]

I may have another go over the weekend and see what happens (I suspect cracking).

 

Adrian

I shall be very surprised if that happens - I have never experienced DAS cracking.

[RhBBob]

Excuse me interrupting this thread but someone in 7mmNGA web group has pointed me to Pyruma for making a mould by impressing, say, a brass handrail in order to produce further copies.  My search for Fire Cement lead me here !!

 

Allan commented here that DAS is basically the same compound; do you think it would do the job, or would the shrinkage referred to, negate any advantage ?  Perhaps leaving the master in the compound overnight would be appropriate ?

[allan downes]

My very limited experience with DAS has been identical, I tried the cobbly thing using a brass imprinter a la Downes and as it dried it pulled up the 2mm card substrate I  had PVA'd to the ply base. I really envy  some of the work I've seen on RMWeb but that experience has put me off. It certainly didn't let go of the card! Allan says he used to use Pyruma [sp?] fire cement before DAS but that gradually crumbled away......I know the feeling.

 

Doug

Hi Doug.

 

What's happening with your cobble press lifting the Daz up off the card base is probably because the press isn't releasing itself from the compound. However, if you sprinkle and smooth the Daz over with Talc, this should allow the press to come away clean.

 

Cheers.

Allan.

[David C]

I've never had any problems with DAS coming away from styrene over very many years, largely because I follow the advice of Dave Rowe, the first person to describe its use in model building very many years ago. All you have to do is wait until the DAS has dried out, then flood it with Mek Pak or whatever solvent you're using.

 

Styrene always needs some kind of bracing, regardless of whether it is coated with DAS - the larger the model, the more there needs to be. If its laminated, one should always ensure that there are an odd number of laminations.

 

David C