Sikaflex 291 Curing Confusion.

[BAD ORCA]

On the data sheet on Sikaflex's website https://usa.sika.com/content/dam/dms...flex291-us.pdf they have a cure rate chart. For a 5mm thickness bond. They say it will take two days to cure at approx 75 degrees/ 50% RH, but in the next column on the same datasheets it says to not totally immerse in water for one week. I was under the impression from some online comments you can go back in the water quickly. Maybe I misunderstood and should have done a bit more research so little confused with that...

I just installed two thru hulls with it today and will do the third tomorrow morning. I estimate that the maximum thickness of Sikaflex for my application could be around 5mm in some places. I beveled the opening of the hole in the hull at 45 degrees to create a thick o-ring seal between the fitting and hull. Thickness between the side walls of the fitting and the hull are maybe 2-3mm thick. The thru hulls do sit flush against the hull though so less than 1mm thickness there. Im using it California and its been pretty much 75degrees and 50%+ RH here all week.

So do i have to wait a week to let it cure before going back in the water or two days, according to the cure chart? Hoping someone who really knows this stuff can clarify this for me...


Thanks

[tkeithlu]

I don't have direct experience with the stuff. How some ever, you're taliking about the stuff actually doing a minimal job - narrow seals around parts that fit together. Test it with your fingernail or a screwdriver. If it's stiff, go sailing.

[tkeithlu]

Second thought. I think what I'm doing is suggesting a more practical and less rule-bound approach. The manufacturer's advice should not be ignored, given that they know the product. Don't expect one-week 3M 5200 to be ready to go in one day. On the other hand, consider what you are trying to do with the stuff, whether it is doing it, and whether (in this case) it has hardened. The manufacturer does not want a customer coming back and saying "I followed your advice and my boat spouted seawater," so he is going to be conservative about it. You can develop your own safety margins for it. It could be that you're anxious about any possible leak, and choose to wait longer than the manufacturer's advice, or you could say "It's hard, it"s OK."

[sv Grateful]

By now you're probably In the water and all is well.

I would imagine that the two days curing gives you a large percentage of fully cured mechanical strength. The other five days may be to allow all out gassing of the curing process to be complete.

As the poster above states, it may just be CYA on the part of the manufacturer. On the other hand, I've used a variety of Sika products, following mfg instructions to a tee with flawless results.

[BAD ORCA]

Originally Posted by sv Grateful

By now you're probably In the water and all is well.

I would imagine that the two days curing gives you a large percentage of fully cured mechanical strength. The other five days may be to allow all out gassing of the curing process to be complete.

As the poster above states, it may just be CYA on the part of the manufacturer. On the other hand, I've used a variety of Sika products, following mfg instructions to a tee with flawless results.

Much thanks for replies.

Yeah went back in this morning. Everything is looking good. The two thru hulls that had the thickest application got 5 full days of cure. The third which had the thinnest application got four full days. I was lucky, where i am located it has been 70-75 degrees for the past week during the days with humidity above 75% the entire time. I feel good that the thru hulls got well cured. The squeeze-out was very firm. The thickest areas of application were right at the hull opening so i think its all good. No leaks at all.

Incidentally, the boat yard also uses 291 and they splash next day. I know they are trying to get boats back in the water asap but they rarely have issues. I think for my keel re-bed i might use 292 instead though. Has better gap filling abilities according to data sheet and cures faster.