There are some chemical methods available for ABS but the equivalent for PLA uses toxic materials so I'm not keen on that.
I've tried Hi Build car primer but it took so many coats and so much sanding that I lost more detail than I was happy with. This time I have tried two different solutions. Resin and normal nail varnish.
I tried two resins. Zap 30 and a resin specifically marketed for the job, XTC-3D. The Zap 30 is a bit too thick and cannot be applied so easily so that leaves the XTC-3D.
If you are going to use XTC-3D I strongly recommend watching the following video first. It's a bit long but has some useful tips.
The most important take out from the video is to spread the mixed resin thinly over a dish. I found that the working time was inadequate at less than 5 minutes from the mixing pot but using the thin layer in a dish it is much longer.
Where I applied the resin while it was still nice and runny it worked well. Even when it is thin it is difficult to get the right thickness. Some areas in my test sample had insufficient resin but I can work on my technique to improve on that.
|Resin was already starting to cure!|
For my purposes the resin needs to set horizontally to self level. The vertical areas pooled and had less satisfactory results.
|Carve out the lost detail|
|Resin took some sanding|
The disadvantage of the resin is that it is still too think and of no use where I have fine detail on the model cars. It flowed in to small holes and shut lines where I did not want it! When set it is hard and difficult to sand. I had to use the Dremel tool which makes it impossible to sand some tight areas without damaging some of the detail! Large flat areas are OK to work on.
|Resin filled the steps on the bonnet|
If I was making an organic shape or there was no detail, the resin would be ideal as it is just one step to a smooth surface. Unfortunately for more man made objects, like cars, it has limited uses.
I will use the resin for the bonnets and any other parts that have open stepped horizontal layers on shallow sloped surfaces but will avoid it elsewhere.
|Resin filled the detail on the side of the wing|
The loss of detail is why I moved on to an alternative.
I tried two different types of nail varnish. A clear top coat and a coloured layer.
The coloured nail varnish worked well. It had the advantage of showing where I had used it and the thicker coating filled the thin layers exactly as I had hoped. Even with the brush that came with the nail varnish, I had enough control to avoid getting it in any of the small details.
|Nail varnish on the door|
Nail varnish dries very quickly so I was able to do three coats in only a few hours and could sand it before the end of the day. It was easy to sand so I was able to avoid too much loss of detail.
The clear top coat was not as good on the layers but I could use it to fill the fine pattern on perfectly horizontal surfaces where the coloured varnish would be unnecessarily thick.
|Nail varnish did not fill the steps|
The nail varnish was not thick enough for stepped areas, perhaps 10 or more coats would do it but I did not try that. Back to the resin for those parts of the model.
One last test was to check how they took paint. I was sure the resin would be OK but I had my doubts about the cellulose based nail varnish. I let both dry over night before spraying on the acrylic primer.
|3 coats of nail varnish on the bonnet is inadequate|
|Nail varnish on the front half of the door works well|
|Resin on the far half of the bonnet fills the step lines|
I needn't have worried about the primer. Both the resin and the nail varnish worked well with no undesirable reactions to the paint.
I had another idea which I didn't try until a bit later. That is to use normal household undercoat. That looks to be a bit thicker than the nail varnish. The undercoat has not dried yet so I'll have to report on that another day!