When painting over black japan stained timber several problems can occur. Read on to find out more
Black Japan was a bitumous solvent stain used to stain lighter timber to a dark, almost black, colour. You will find Black Japan stained timber in older houses on floors and skirting, architraves and doors and it was often over coated with shellac to give a gloss finish.
When it comes to painting Black Japan finished timber there are several things that you need to know. If finished with shellac you will find that with a light sand, undercoat will stick very well to the shellac, however the shellac itself is very brittle and you may find that it will chip if stuck with a hard object. The only way to prevent this, long term, is to sand the surface back to bare timber and start again. If the Black Japan is not coated with shellac then there is a high probability that the stain will bleed through most paint products that are applied. If this is the case then your options are layer up as many coats as needed of a pigmented shellac based stain sealer such as Solver Multiblock Stain Sealer or Zinsser BIN Primer Sealer. you could use pure shellac instead of a stain sealer but you won't get any blocking of the colour only the stain so you will need to apply a coat or two of undercoat as well. If there is still a problem with stain bleed and sanding it all off is not an option, then you can coat the substrate with an aluminium paint, such as Wattyl Killrust Aluminium, and the interlocking flakes of aluminium tend to be a very effective barrier to the stain bleed.
If sanding the Black Japan off is the best way to remedy your problem then be prepared to use up a fair bit of sand paper as the bitumen tends to clog it quickly.