Sikaflex 291 curing confusion.

[BAD ORCA]

Posted this on another website as well but not getting any replies so will try here also since time is an issue.

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 here you can go back in the water quickly (two days according to the chart). Maybe I misunderstood and should have done a bit more research, so little confused with that...On the data sheet for Sika 292 it has the same cure chart but omits the part about waiting a week.

Anyways I just installed two thru hulls with it yesterday and will do the third this 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 in 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...

 

[jssailem]

For something as critical as this is, I would consult the manufacture about their product.

 

[dlochner]

Are Sikaflex 291 and 292 the same product? It may be that one formulation requires an extended cure time and the other does not.

For something as critical as a through hull, follow the manufacturer's direction. If it fails you will have a bigger issue than waiting a week on the hard.

 

[Tally Ho]

The data sheet for 291 also includes the 1-week wait time for total immersion.

Sorry, the page you are looking for does not exist or has been moved

usa.sika.com

As @jssailem said, this is a pretty critical application (assuming the thru-hulls are below the water line). I would be waiting to make sure the stuff was properly cured. It appears it is dependent on humid for the cure, so in colder temps, it takes longer…maybe there is a big safety factor built in to the 1-week…but not a good location to take a chance.

I used 291 on my above the water-line thru hulls…great stuff. Cured over the several weeks in the spring before I launched.

Greg

 

[BAD ORCA]

Ok thank you for the replies. I would rather be safe than sorry so will heed the advice and wait it out. I do need some small fiberglass repairs done so i will try and have that done and maybe save some $ on yard fees.

 

[Scott T-Bird]

Like concrete, polyurethane based adhesive/sealants fully cure over a time period that is generally defined by a curve. The curing diagram shows that 5 mm thickness at ideal curing conditions is 2 days. You can count on it if your thickness is consistent (or you are going by the maximum) and curing conditions are ideal. The 1-week period gives you a factor of safety. Only rarely is a product like this applied with perfect consistency in thickness and immersing the product in water, for which it is intended, is at the extreme end of its use spectrum nevertheless. Many applications will merely be exposed to moisture, not completely immersed. I would be more comfortable waiting the week, but if I had to put the boat in the water in 2 days and no later, I think I would not be stressed over it, either. Keep in mind that once it is immersed, curing may be aborted, hence the factor of safety is more important. If the product is not immersed, it continues to cure whether or not it is placed in service, so the risk of ultimate failure is not as significant.