Join Date: Jul 2000
Thanked 258 Times in 244 Posts
Rep Power: 18
Re: Black spots on the wood
Youre going to have to define better the black spots a bit better, their location in proximity to scarfs, bungs, joints, etc. ... and if the dark was UNDER any surface coating before you removed the varnish, etc. If so this a moisture condition that may be coming from BEHIND the wood and if the source of the moisture is not remedied no amount of bleaching, sanding or other prep work then recoat will be effective to last long ... until you remedy the moisture from getting behind, then migrating 'through' the wood or coming from behind the BAD joint. If the leak is from behind ... I sometimes apply/inject liquid clear 'athletes foot remedy' (look for the TIN content on the label) to kill off any mold that is 'inside' the wood (look up: "wood + spalling" ... or ... "wood + spalting") so you know what to look for. Spalting is wood that has been deeply penetrated and discolored via fungi.
If the black was created from a 'surface' leak of the prior coating being faulty ... TSP, oxalic, etc.
If this is 'really' surface mold/fungi, then TSP and/or sanding, followed by oxalic acid or clorox, etc. Teeny black specs. (lot of them) are usually caused by artillery fungus ... a fungus that lives on tree bark in cool humid climates - TSP followed by bleach.
Could also be a 'sap pocket' that was undiscovered in the original installation ... good luck with that.