Finishing balsa solids

[Balsabasher]

Things seem a little quiet around here so time to do a little tutorial on finishing,many fight shy of working in balsa due to the extra attention it needs as regards finishing,however if tackled in the right way excellent results will be achieved with a little knowledge and patience,so lets go through a few of the necessary steps to achieve the desired paint finish,many of these tips have been hard gleaned over many years of modelling and I hope that they will serve as a basis for a better understanding of working with the wonder wood balsa.

The first thing to remember is that any dings that happen during the carving and sanding need not remain,all you need to do to pop out these marks is to dab some water with a brush on the offending area,after a few hours the wood is restored ready for a further sanding,once this has been done and you are happy with the surface it is time to initially seal the balsa using the well known sanding sealer mixture,you can easily make your own sealer by obtaining some non shrinking clear cellulose and adding talcum poweder to the desired mix,I say desired because it is personal preference as to how much to add,experiment by using a scrap of balsa and applying a coat to see how it dries,once sanded it should leave a silky finish on the wood that is what we are aiming for,mix up enough to be able to submerge major components totally held with a loop of wire,allow the sealer to drain off back into the tin/jar,this method of sub sealing before assembly is especially useful with biplane models where it can be difficult to get at between the cabane struts etc,each part is treated as a seperate unit and sanded down before final assembly.

Once the parts have been suitably sealed with the dope/talc mix now is the time to start the primer process,I use rattle can grey auto matt primer excellent for our purpose,shake the cans well and spray outside on a calm warm day,once the first few coats have been added any blemishes etc can be treated with a knifing putty,you can buy tins of this from your car auto shop and it lasts for a long time,leave overnight to cure and sand down smooth the next day,you just cannot rush the finishing stages on any model as it needs to be done carefully,keep sanding and checking until you are happy to proceed to the next stage of applying wet strengthened tissue to the surfaces.

As wet strengthened tissue is not easy to get hold of any more a fine alternative needs to be sourced,you need go no further than your local garden centre for this and it comes in the form of very fine fleece that is used to protect plants etc on cold evenings,go for the finest that you can find the thickness of ordinary tissue paper,this is very cheap and comes normally in large rolls that you just cut off what you need,a few yards will last a long time,you can purchase it already pre wrapped but this has crease lines in the folds so best to buy it straight off the roll.
Now cut portions of the tissue just oversize to the components being dealt with and smooth the piece out over the surface,take a well water charged brush and dab through the tissue once again smoothing it out as you go along,aim to just extend past say the wing trailing edges or wingtips,we can deal with those at a later stage,next take another brush and using clear cellulose dope charge the surface through the tissue,this will stick it down nicely,smooth out the layer with a lint free cloth or similar and watch it turn a milky white colour ! do not worry because this will vanish upon the next application of dope and leave a smooth surface.
To trim the edges take a sanding block and run all around the shape of the wing to remove the surplus tissue,it will be just cut away with the sanding operation and give enough edge to add dope to the edges and fair down with your finger.

Leave the whole lot to dry out overnight and then inspect the surfaces for blemishes,sand down as necessary,now it is time to reach for the grey primer again and add a coat over the whole lot,this too will show up further blemishes so deal with them accordingly until you are happy.
Keep adding primer sanding in between the hardened coats,this can take weeks but as I work on several models at different stages of construction this works out well.

So finally you will have the necessary surface to add your chosen colourscheme.

Barry aka Balsabasher.