| Lets take glue as an example of something that we all learn hard lessons with and is a topic that we are all learning as we progress in our hobby. I only recently discovered that Rapid Araldite is not considered as waterproof and yet normal cure Araldite is. I have had to try to rectify this with some additional resin and paint on the steam coaster hull but it would have been nice to have this knowledge before hand.
So lets look at one very small area of glue and consider why we have polystyrene cement and liquid poly. Both do the same job, which is to melt the surface of the polystyrene plastic and allow the two surfaces to fuse together but are there any reasons for using one over the other? We can easilly fall into the trap of considering cement as old fashioned and out of date but it still has a place in our modelling boxes today. I have seen youngsters buying a kit and preparing themselves with all the paints, glue, brushes, knives etc so it makes me wonder if they realise that the glue they have purchased may not be the best for the job.
Basically both glues are an active polystyrene solvent but one is dissolved in a highly volatile vehicle with the consistency of water and the other is dissolved in a thick gel vehicle.
The advantages of the liquid poly are that is has amazing capillary action so it will run into a closely fitting joint, which has been pre-assembled, with just a touch of the brush on the joint. It dries very quickly and leaves no residue afterwards and so holding joints together while they dry does not require the same length of time as cement. It is very clean and easy to use and it generally does not cause any stringing effect. Painting over the joint will leave no indication that the glue was ever there. Disadvantages are that it will not fill gaps so if you are joining large, inaccurate faces it may not completely fill the gaps and render the joint weaker.
Polystyrene cement on the other hand fills gaps very well due to its thick consistency and can be used liberally on a large joint to cause a build up of cement outside the joint. This can be sanded down afterwards to give a perfect seamless finish or, if the joint is not in view, the bead of glue can be left to give additional support to the joint. Disadvantages with cement are that it takes a lot longer to set completely so pieces require support for a lot longer and it has a tendency to cause stringing, making it more difficult to use.
As a couple of examples, to glue a detail to a ships deck of say a davit, it would be best to assemble the detail dry and then brush the joint with a spot of liquid poly. On the other hand to assemble the two halves of the hull it may well be better to use a bead of cement, which could be smoothed down afterwards and even an additional bead could be run down the inside surface of the hull.
The picture shows a water tank to be fitted to a model boat that had to be completely watertight. It is out of sight so I used liberal amounts of cement on both sides of all joints and cleaned the outside very little. |