Hi Chris,
Thank you for your as always thoughtful posts and your experience dealing with the sealer you have in your tank. i suspect "Fertan" tank sealer is a product used in Europe, so wonder what made in america product would be same or similar. i also note, unfortunately, Fertan is not sipped to usa. so.... i wonder what the active ingredients Fertan in UK is made up of...... doing a quick google search, Fertan in usa is a rust remover. Chris, anything on your Fertan container give ingredients?
i've prepped and sealed around 50 tanks in my time, most of them when i worked for a local motorcycle repair shop, used different sealer products on 5-10 of my tanks. without exception, i believe all sealer products are good. in the case of the probably 25 sealer failures i have seen, without exception, is because inadequate prep was done prior to installing the sealer and inadequate prep is, without exception, due to lack of thoroughness and patience on the part of the individual doing the work.
This topic could entail a very long post on a number of different topics related to tank prep; i have neither the time or desire to do so.
Despite all the garbage written on numerous websites by people who lack experience, critical thinking skills or are simply keyboard commandos off-gassing, there is no dark secret nor black magic to remove rust from a tank. In my experience, what there is, is a number of very effective ways to remove rust from a motorcycle gas tank, i'll cover briefly at the end of this tale.
sealers such as kreem, red-kote and por-15 are all methyl ethyl ketone based and as such, mek or acetone does readily remove these liner products.
caswells is a 2 part epoxy and as such, mek will not touch it. after i wrote the above thread, i did call caswells and they confirmed what i already at least thought correct; methylene chloride is supposed to remove caswells. so, i ordered 1 gallon of methylene chloride which arrived yesterday and i now have fragments of caswells in a glass jar with the methylene chloride, which, after 36 hours does not appear to put much, if any, of a "dent" in softening or bringing the caswells into solution with methylene chloride.
this being said, feeling desperate that methylene choride does not seem to affect caswells, earlier today i purchased one gallon of a paint stripper product available in america, "zip-strip" (knowing it also contained methylene chloride). like i said, i am feeling desperate, but my past experience told me it is highly effective removing rock-hard dried gas in gas tanks, so what the hay, huh? i've used zip-strip numerous times in the past for paint removal. reading the back of the can, the active ingredients of zip-strip are methylene chloride, methanol and mineral spirits. subsequently, i added equal parts of zip-strip to the jar with methylene chloride and caswells fragments. i should think 24 hours should be sufficient time to see if this brew takes caswells into solution.
well..... this is longer than i wanted to take writing but i will share a few bits of my experience using different sealer products.
kreem: if a tank has pinholes, kreem is what i suggest using. semi-viscous out of the can and as it is applied, the mek will evaporate off so a thicker coat can be applied and need be is readily thinned by adding a very small amount of mek. application of kreem is not readily affected by temperature variations, 10 or slightly more degrees (F) one way or the other will not adversely affect viscosity. dries semi-white opaque depending non how thick you apply the coat(s). a coating of kreem can be as thick or thin as you prefer; from opaque white to white. i have seen kreem jobs that look as good 20 years after application as if they were the day before. personally, with tanks i've applied kreem to, i've not yet experienced failure with kreem. never sets up hard, always has a bit of elasticity.
red-kote: other than being clear and red and slightly less viscous than kreem, otherwise seems to respond same as kreem. leaves a clear red coat which can be made thicker with prolonged rotation, but not as readily thicker coat as kreem. (whether kreem or red-kote, do not leave excessive pools of it on bottom of tank; drain as well as possible. if you feel there the coat is excessive, add a small amount of mek to thin so you can pour out excess). antique motorcycle guys swear by red-kote; they use it in 60-110 year old tanks. i applied the stuff to my pair of 1927 gas tanks; first time i've ever used the stuff, but i followed in the footsteps of those more experienced than i who report good results. never sets up hard, always has a bit of elasticity.
por-15: pretty runny, definitely no like water and definitely less viscous the the above two sealers. is more sensitive to temperature variations affecting viscosity and without exception leaves a thin silvery sort of hammerloid-appearing coat. if you have multiple small pin holes you want to seal, use por-15 at your own risk for failing to seal holes. i used por-15 on 2157 tank, after 9 years it look as good as the day i applied it. sets up hard.
caswells: clear, so really dificult to see if all parts of tank are coated. very sensitive to even 5 degree temp variations so within these temp ranges can be nearly runny as water and thick as syrup. because caswells is a 2 part epoxy, it begins setting up within 10-20 minutes (depending on ambient temperature) and if you wait too long, the excess becomes increasingly difficult to drain out (i suspect because when the 2 parts are mixed, a sort of catalytic reaction begins). once set up, hard as glass. it has been 14+ years ago i applied caswells to my little yamaha tank, looks as good as the day i put it in.
what i have learned about manufacturer's prep and application instructions: they only give the basic or general idea for tank prep; none consider severity of tank interior and other factors. caswells instructions to "place a hand full of sheet rock screws" to remove rust is and "to plug outlet ports with putty or Play-Doh" IS SIMPLY RIDICULOUS. actually, their advice is simply f---ing ridiculous. otherwise, sealer manufacturer's prep and application instructions are woefully vague and woefully inadequate.
based on my experience, i firmly believe everyone of these products are excellent ONLY IF PREP IS PERFECT. what users fail to realize when it comes to prep, there are many ways in which prep can be carried out. I ONLY USE A LINER WHEN I BELIEVE THE INTEGRITY (STRUCTURE) OF THE TANK IS COMPROMISED. otherwise after i have rust out, i keep bare steel. regardless, i always keep my tanks filled with gas and in bikes i have in long term storage, i oil the inside. mind you, i live in semi-arid conditions, so i don't have the humid conditions others must contend with.
as far as blaming ethanol gas on liner failures, myself i believe that is a convenient excuse to not account for tank prep appropriate to the needs of each particular tank. in other words, poor tank prep causes liner failure, not ethanol gas. i've personally seen (and heard of) many a lined tank containing ethanol gas hold up for years without a problem.
for those considering using any tank liner product, I CANNOT STRESS ENOUGH THOROUGH TANK PREP. there are quite a number of different ways to prep a tank and the reason a tank needs prepped is usually because the inside of the tank is rusty. regardless, the last thing i do before the final DRYING rinse, is i always rotate (sometimes 2, 3, 4 and even 5 cycles) the tank in an old clothes dryer i have; the tank being rotated containing twenty-five 1/2" nuts and twenty-five 9/16" nuts to dislodge anything my tank prepped may have failed to. (DO NOT use a nut larger than 9/16" !)
i will touch only briefly on rust removal and tank prep procedures i have used:
1. 3% phosphoric acid solution as comes with kreem, red-kote, por-15.
2. reverse electrolysis
3. molasses
4. "wood," i.e., oxalic acid
regardless, i always do the rotate the tank with nuts in it routine. (i used to try to shake the tank by hand and all that did was wear me out.)
when it comes to tank prep and especially installing the liner, have your step by step plan all laid out. have effective fool proof ways to block openings. once i am satisfied the sealer is somewhat set i open up all orifices and put a fan to the tank to help circulate air through tank. and i check routinely to make sure any residual sealer is not pooling; again i rotate.
in closing, depending on the tank, prep, depending on approach, can take anywhere between 5 and 25 hours spread over usually no less than 3 days and up to 6 weeks. good tank prep is tedious, time consuming and requires near if not continual attention, as well as patience, persistence and perseverance. good tank prep requires a well thought out step-by-step process before starting the process; especially the lining process. pity anyone who is dealing with a lovely painted tank.......
well....... it's been over 2-1/2 hours the caswells has been soaking in my methylene chloride/zip-strip brew since i started writing this novel. hard to tell if "the brew" is making a difference. shall report back.