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Re: Sun block on fiberglass
Capta - here's my 'supposition' of what caused the 'yellowing' and what to do about it, at least you can 'trial' the remedy to see if my suspicions are correct.
Suntan lotions today probably use nanoparticles of a form of soluble iron as their UV blocker - nanoparticles of ferrous oxide, the same as used as UV blockers in 'varnishes', etc.
Secondly the 'carrier' in most cosmetics are simple botanic oils.
The combo would require a 2-part extraction process.
First you probably have to extract the 'oils' - apply a wet 'paste' of simple laundry detergent, cover with clear plastic wrap and tape the edges with masking tape (during the trial). Let sit for a day for the oils to become emulsified. This will 'emulsify' the oils, leaving the UV blocker - the probable 'yellow'. The progression in increasing 'strengths' would be: dishwashing detergent, paste of laundry powder, TriSodiumPhosphate - TSP, an undiluted SodiumSilicate based detergent, lye (dangerous).
Most acids will dissolve 'iron'. from fairly weak to strong: 'lemon juice', vinegar, citric acid (from powder), oxalic acid (from powder), muriatic/hydrochloric acid (dangerous) .... and then if needed clorox. The acid treatment results should be almost instantaneous, if the oils are first removed.
All the above is chemically compatible with the polyester and vinyl ester used for gelcoat.
Choose which of the 'trials' seems to be the 'best', then ....
If any of the increasing strength 'trials' is sufficient, then apply broad scale of the 'selected agent' to the areas .... no need to cover; but, just keep 'wetted/spritzed' with a 'mist' from a dock hose to prevent drying, but not so much as to rinse off. Soak time or 'wetted-time' will be important.
hope this helps.
Last edited by RichH; 04-22-2016 at 10:00 AM.