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Re: Teak stain issue
If the teak is solid teak and the end grain was exposed at the bottom and the strakes were semi-immersed for a long time .... what probably happened in a worst case scenario is called 'spalting' or migration of fungal filiamentous growth along the 'water channels' of the wood. Since if its teak there will be little bungal damage per se but the 'stain' from the fungus will be very hard to remove if especially the spalting is deep.
Rx: small trial on an incomspicuous spot -
soak with a mixture of TrisodiumPhosphate -TSP to 'dissolve' the funal seccls and oxidized teak surface cells ... this will extract tannis from the bare wood so the 'effluent' of the wash may be brown. Start with diltuted mixes of small amounts of TSP dissolved in a high proportion of water ... and slowly 'work up' to heavy dose of TSP ... what youre looking for is a diminshment of the 'spalting' ..... dont worry about the teak color at this time. The job is dissolve the fungus that's inside the wood.
If the TSP affects reduction of the spalting, then rinse well and apply oxalic crystals mixed into hot/warm water and do a trial bleaching to remove possible iron staining and possible tannin migration staining ... the tannins migrated within the wood 'channels' when it was water saturated. If that comes close to 'clearing' the stain, then let the wood dry and attempt to sand the wood down to see if the staining is deep or surface staining. If deep, consider to paint the wood if its 'that ughly'.
If only surface deep, do the entire surface, but light sand away any varnish before treatment with TSP and Oxalic.
Once cleaned, bleached, rinsed, dried and sanded, You 'can' then begin to color match the differences. Use very very thinned out stains on the worst color affected section and slowly and constantly keep working and wiping on/ wiping off the stain until you get a good color match ... may take several days of applying, wiping and drying to reach the 'match'. Dont apply the stain all at once, use very thinned out stain ... and then think what primary color - RED, blue, yellow is missing or is too 'strong' as the color 'develops' and you need to change the 'hue' of the stain youre using.
Read the cautions on each container of TSP and Oxalic carefully. Dont mix TSP with oxalic. Wear gloves, goggles, etc. when using either.
Good luck, be patient but persistent.