Tacky epoxy

[alyeska]

I have one area of a inside hull layup that remains slightly tacky weeks later. Temp at time of layup was around 18-20 deg c & have since warmed up shed to 25 deg for a few hours at a time. Whats best, another coat of epoxy, more heat or something else?

[apex1]

Could it be amine blush? A cloth with vinegar would remove that! Otherwise I guess your mixture ratio was imperfect. I have no clue how to "repair" that. I first would try temperatures above 50°C to postcure properly.

Regards
Richard

[gonzo]

You got to remove it to be sure. Epoxy should not be tacky. Usually grinding is not possible because the discs get clogged too fast. A scraper and a torch seems like the best way.

[Guest20100203]

I'll second Richard and Gonzo's comments, though you may have success at 45 degrees, for several hours.

The only repair if it was an improper mix ratio is to remove the uncured goo, by what ever means (scrapping, sanding, cussing), then prep the surface again for a new epoxy coating. You can't save it (unfortunately) with more hardener or resin or over coating, it has to come off, if it's not "kicked".

I know this probably isn't what you wanted to hear, but it happens to us all, except Richard, who is too expert to make these types of mistakes.

[alyeska]

Thanks for the feedback. I'll try some more heat for starters before removing laminate. Rest of layup went off ok just this one area thats not right. Probably didn't mix properly.

[alyeska]

Gonzo, won't be able to remove with scraper & torch as corecell would be damaged.

[Jimbo1490]

Use a coarse wire cup brush on a big grinder. Wire brushes do not clog, even when removing fairly tacky substances.

[gonzo]

Epoxy resin penetrates the open pores of the corecell and is part of the bond. Even if you take the sticky resin and fiberglass off the surface, the bond will never be good. You need to cut off the core and replace the section. It is not too difficult to set the depth on a saw to a bit less than the core thickness and then chisel it out.

[Itchy&Scratchy]

A common mixing problem is that people see its a ratio of two to one so they weigh it out , when more often than not, its two to one by VOLUME , which is different.

J

[masalai]

epoxy is by weight (well the stuff I get from ATL) and weigh accurately on digital scales with the container zeroed out... Good idea is to have a light/thin plastic bag over the machine and replace regularly as spills fall on the bag.... Mix thoroughly with a long metal mixer attached to a CHEAP electric drill (the drill will stuff up in 4 months because of epoxy drips and spills etc - - the metal stirer can have the epoxy burnt off every so often and whilst hot, spray with water and will look like a new one

The other posts are correct, ALL the sticky part must be removed as it, and all sticky bits are now rendered useless...

[alyeska]

Thanks for all the advice, will set up a insulated cover over the hull tomorrow and try heating up & see how that goes first. If we have to cut out dodgy area it won't be too hard to fix as outside skin is not done yet and new foam can be attatched to basket mold & reglassed.
Are using SP epoxy with mix ratio of 100;28 by weight, have been using electronic scales for mixing but suspect got one batch wrong or temp on the day was'nt warm enough for long enough to set off properly & since then has only been around 12 to 15 deg c.

[apex1]

Originally Posted by PAR

but it happens to us all, except Richard, who is too expert to make these types of mistakes.

Nahh, it does´nt happen to me. I let the mistakes be made, I do´nt make them myself.

And I would´nt go too low with the postcure temperature! If there is a chance to save the part, it will be higher at higher temp. So 70°C is better than 50°C.

Richard

[Herman]

Indeed, do not make all mistakes yourself. Give someone else the opportunity to make mistakes as well...

First try if it is amine blush. This would safe you a lot of work.

Otherwise heat up. If it cure completely, it was the low temperature. If it start to "melt", it is a bad mixing ratio, or bad mixing.

Common mistakes:

-not resetting the scale to zero
-calculation error
-wrong mixing ratio assumed (volume / weight)
-bad mixing. The bottom and sides of the container need scraping as well. always transfer the epoxy to another container after thorough mixing, and use that for laminating / coating.
Finished with mixing? Satisfied with the result? If so, mix for another 30 seconds...
Take a news paper. If you can read the newspaper through the epoxy, then the mixing swirls are gone. (you need transparent mixing cups for that, and you need to be able to read...)
-Clogged dosing pumps, I mean those small screw-one ones on jerrycans (I do not like them...)
-Refilling the epoxy dispensing system with different epoxy, or mixing up resin and hardener.
-Mixing up resin and hardener altogether. (2:1 means 2 parts resin, 1 part hardener, not the other way round)
-Forgetting to mix in hardener altogether.

I am still young, but I have seen them all happening. No-one is error free...

[alyeska]

24hrs at 60 deg C did the trick, all tackiness has gone & laminate bonded to foam well.

[apex1]

Originally Posted by alyeska

24hrs at 60 deg C did the trick, all tackiness has gone & laminate bonded to foam well.

Congratulation! And well done to go for a bit higher temp!

Richard