DrWatson 375 Posted June 30, 2011 Share Posted June 30, 2011 Hot on the heels of my last tech issue comes another: Polyurethane over Epoxy. I have chatted to Wheels about this and we've decided to open it up on the forum so some gurus might offer assistance. The bottom of the skiff is 206 West epoxy impregnated/coated 4mm ply. We've sanded, wiped, washed, wiped and dried it. A day later it was coated with a layer of Goldspar, thinned about 10% with #1 thinners. It dried up nice and the next day, well into the overcoating time, we applied another layer also thinned about 10%, then lifted her up on her straps in the garage and left for two weeks. Thing is, after two weeks some of it hasn't dried properly, but only in patches. Some of it is perfect, and some of it is rubbery and sticky like dull sticky tape. WTF! Comes off like cold snot under a fingernail Most depressing, disheartening and frustrating. The issue is, what went wrong, and how? And now what do I do with a boat which is half sticky and rubbery and half hard and good? I'll check this weekend to see if it has set any more but I kinda doubt it. Is it possible I over thinned it? R Link to post Share on other sites
rigger 47 Posted June 30, 2011 Share Posted June 30, 2011 I do not think you over thinned it - we used to use an 50/50 mix and even as much as 80% thinners with Goldspar, never had issues of it not drying. removing it - not sure on best way - someone else may have come across this issue and have the solution. Link to post Share on other sites
Guest Saturday Night Special Posted June 30, 2011 Share Posted June 30, 2011 I have come accross this with varnish before and it was my own fault it was whwn I appl,ied it late in the the evening and a the air was cold and damp Link to post Share on other sites
TimW 1 Posted June 30, 2011 Share Posted June 30, 2011 Sounds like the Epoxy is not yet fully cured. west 206 needs quite a while to dry, at 20 degrees C I'd say 24 hours would do it, for every 10 degrees less Air temperature double the overcoating time. You can't paint over under cured Epoxy. The Gases emerging will inhibit the paint cure. the explanation for the paint being sticky only in some areas is that the Epoxy is probably not perfectly mixed and the areas you have the most problems in are probably the least cured areas of epoxy. Link to post Share on other sites
khayyam 68 Posted June 30, 2011 Share Posted June 30, 2011 ah. i missed the "a day later" part before. i think maybe timw is onto it. where are you doing this, and what's the temp? the epoxy i've applied most recently needs several days to cure at 15C and 96 hours(!) at 10. Link to post Share on other sites
Terry B 71 Posted June 30, 2011 Share Posted June 30, 2011 I'm no expert - but I spoke to International Paints a year or so ago about a similar problem I had - but not on the scale you have - that's gotta be frustrating. They gave me a list of possibilities: 1. Epoxy not fully cured - this was the culprit I think in my case - even though I waited 3 days - it was winter, cold in my outdoor garage.......... 2. High humidity - the boat may have areas around it that have less humidity than other areas (e.g. colder areas where there's less air movement) 3. Damp - it's just plain to damp - 4. Applying to thick - tricky this one - it's hard to get it even when you've got horizontal and sloped and vertical surfaces. They said too thick a coat is a classic for not drying. 5. Too hot or to cold............. The cure (in my case) was to wipe off the uncured with white spirits, allow to dry FULLY, then sand and recoat................. Hope this helps. But as I said I ain't no expert. I'd get hold of the manufacturer.................. Good luck, it's a bitch when this sh?t happens. Link to post Share on other sites
DrWatson 375 Posted July 1, 2011 Author Share Posted July 1, 2011 Thanks for the advice. My first thoughts also were that the epoxy was not right but it was applied at least three weeks before the Goldspar, so I'm pretty sure it was cured. It was nicely sanded also. We always mix the epoxy for at least two minutes and measure with the west dosing pumps, carefully primed to make sure a correct mix. It's between 20 and 30 °C around here at the moment, so I don't think heat was a problem. We were working inside the garage, serious concrete construction, and it didn't seem too humid, esp here in the middle of a continent where the humidity is rarely above 70%. Didn't measure it though. Glad to know it's unlikely to be the thinning. I was a bit worried about that. It is possible that it went on too thick, but I would like to think it didn't. Of course it's hard to tell exactly with a brush, spray might be easier. Odd thing is, the perfectly horizontal surfaces under the wings (painted upside down) were the best bit. Dried perfectly. Was wondering if the Goldspar might be too old, but then it wouldn't have cured properly in some places and not in others. I'll scrub off the uncured with white spirits and dry it out. it is bl0ody frustrating though. Link to post Share on other sites
grant 40 Posted July 1, 2011 Share Posted July 1, 2011 there was a big discussion about this on the forum http://groups.yahoo.com/group/jwbuilders/ you will need to log in but lots of experience there with what you are talking about, if you search the discussion you should find all the answer too, good luck I think what you are looking for is info on "Amine blush" Link to post Share on other sites
wheels 543 Posted July 1, 2011 Share Posted July 1, 2011 It is certainly possible that anyone of the points listed above could have caused a problem, but with Doc being...well....a scientist(so therefore would have shaken and stirred everything to the T) and seemingly had ticked all the boxes, I was at a loss. And most products theses days are made to be fairly forgiving to accomadate the "non proffesional applicator". Even Epoxies these days are either solvent free and should not cause this kind of problem and Doc gave it a wash and sand, which is more than most do. Simple things like too thick a coating would still dry. The coat may stay soft longer, but the surface would not be sticky like this situation. Even age of the paint, if it was sealed, it will last indefinately. The only long shots I can think of is that the small garage was too well sealed and no air movement. But after a week, i would have expected the stuff to still dry.And opening the door and allwing some fresh air in should have solved the problem anyway. Or, theThinners were not compatable with the product for some reason, but once again,most of those situations leave a soft coating, not a sticky one. Now having said all that, I have struck this problem once when I was a teenager and had no clue then. My younger brother painted his boat with Epiglass and they were old tins. He didn't prepare very well and we had no idea what the paint was underneath. The coats never dried. Ever.They stayed sticky for weeks. Never knew why and wasn't my problem, so never looked into it. Link to post Share on other sites
k88 7 Posted July 2, 2011 Share Posted July 2, 2011 just something to check, my boatbuilder have to redo my rudder bearings, the epoxy will not set properly in some areas, part of it set but not all of it. Took us a while of head scratching, finally found the root cause, the measuring pump((quite old) was inconsistent, we have to remove the bearings cleaned it all out and start again with new pumps. Link to post Share on other sites
rob denney 0 Posted July 2, 2011 Share Posted July 2, 2011 Be surprised if it is the epoxy (10 years selling it, witnessed every concievable stuff up, not once was it a materials problem). Bloom would stop it adhering, but not inhibit the cure, and the first coat went off ok. Assuming the second coat of paint had thinners from the same can, I would be looking at the rags used to wipe it down before the second coat of paint (thinners can affect the material and the dye), the container the paint was mixed in (maybe not clean) and the brushes and what they were cleaned with between coats. Sounds unlikely, but could also be some contamination blown in from outside. We had this once with air borne silicone being blown in from the shed next door. Link to post Share on other sites
wheels 543 Posted July 2, 2011 Share Posted July 2, 2011 Good comments Rob. For those coming up with the ideas, which are all good comments and valid in many instances, please understand that in this case, the Epoxy cured well. It was washed and sanded before applocation of the Goldspar. If it wasn't cured, it would not have sanded. The first coat of Goldspar dried just fine. No patches of sticky, first coat just fine, second coat is the problem. If thinners was an issue, then the first coat would not have dried correctly either. First coat OK, second coat patchy. Link to post Share on other sites
Guest Posted July 2, 2011 Share Posted July 2, 2011 by txt get dr watson to call me re his varnish problem. It is either age, mixing or a driers (cobalt/ziconium)issue. Possibly not aware of your location but sounds like he knows something, pm me and I'll pass on the phone no. 9 Link to post Share on other sites
wheels 543 Posted July 2, 2011 Share Posted July 2, 2011 It is either age, mixing or a driers (cobalt/ziconium)issue. eerrrr...that would be 0800 FUKUSHIMA Link to post Share on other sites
Guest Posted July 4, 2011 Share Posted July 4, 2011 From our phantom txter: Tell Wheels zirconium is a drier in paints,it probably fell out of suspension during application, thus the patchy areas of non cure, could be too much or wrong thinner. Google driers in paint and voila!. Dr Watson may have to scrape and sand back to sound base and buy new tin - bugger! Link to post Share on other sites
Atom Ant 0 Posted July 4, 2011 Share Posted July 4, 2011 I know who the phantom texter is! He knows his sh*t I reckon. But I'm keeping Link to post Share on other sites
Kestrahl 6 Posted July 6, 2011 Share Posted July 6, 2011 I did some goldspar over everdure recently with no problems, I always mix epoxy by weighing, had a couple of bad experiences with resin pumps. Link to post Share on other sites
DrWatson 375 Posted July 12, 2011 Author Share Posted July 12, 2011 Well, After all this and four weeks of sticky Goldspar, the problem has indeed been nailed down to driers falling out of solution, most likely through heterogeneous dispersion through the bulk (and thinned) polyurethane. This gives the patchy Cure-here-not-there effect that I have. stuff from the bottom of the "mix" dries well, from the top of the mix doesn't. simple really. Fault for this is most probably and embarrassingly mine. Take home lesson is to stir and stir again with an efficient lifting motion, and if thinned to remember that the driers will fall out even faster! Stir well again before removing more from the parent tin, to ensure homogeneity. Weighed the boat on Sunday. With deck hardware, but without sails spars and cordage we're at 48 +/- 1 kg. Mast is coming in at around 8 kg with all fittings. She's going to be a rocket all right! Link to post Share on other sites
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