Sika 291

[vladkri]

Greetings,
Last spring installed bunch of plastic Trudesign thruhulls onto FG boat using Sika 291i black. Did not use any primer or activator. Summer on the Lakes and back to the yard. Last week while prepping hull for new bottom paint noticed that Sika squeeze out outside around fitting mushrooms turned into gooey mess. I used Interlux 216 solvent on the hull, but did not touch the mushrooms. Some vapors sure could be floating around the fittings. On the inside the sealant is solid rubber. Last year care was taken to use fresh sealant. Remembering 3M 3000UV disaster some years back, did anyone experience Sika 291i failure i.e. un-cure? From my experience there isn't any accessible to general public solvent which would dissolve cured PU. The 216 is rather mild.
Any thoughts? Thanks

[User 09]

Originally Posted by vladkri

Greetings,
Last spring installed bunch of plastic Trudesign thruhulls onto FG boat using Sika 291i black. Did not use any primer or activator. Summer on the Lakes and back to the yard. Last week while prepping hull for new bottom paint noticed that Sika squeeze out outside around fitting mushrooms turned into gooey mess. I used Interlux 216 solvent on the hull, but did not touch the mushrooms. Some vapors sure could be floating around the fittings. On the inside the sealant is solid rubber. Last year care was taken to use fresh sealant. Remembering 3M 3000UV disaster some years back, did anyone experience Sika 291i failure i.e. un-cure? From my experience there isn't any accessible to general public solvent which would dissolve cured PU. The 216 is rather mild.
Any thoughts? Thanks

How much time did you give it to cure before putting boat back in the water? Sika 291 needs time to cure and can take a week depending on the environment. Sikaflex has a cure chart available that should be closely followed if using it for underwater fittings. If you splashed right away, I would think the Sika on the outer hull side would have been prevented from reaching full cure. It may have skinned around the thru-hull and cured a millimeter or so deep, but maybe not further than that.

[GordMay]

Sikaflex-291 is a non-sag 1-component polyurethane, which cures on exposure to atmospheric moisture.
Allow minimum of 1 week full cure prior to total water immersion situations. Avoid contact with alcohol and alcohol containing solvents during cure. [* under ‘Limitations’]
* ➥ https://productimageserver.com/liter...de/67311QG.pdf

[vladkri]

Originally Posted by GordMay

Sikaflex-291 is a non-sag 1-component polyurethane, which cures on exposure to atmospheric moisture.
Allow minimum of 1 week full cure prior to total water immersion situations. Avoid contact with alcohol and alcohol containing solvents during cure. [* under ‘Limitations’]
* ➥ https://productimageserver.com/liter...de/67311QG.pdf

Yes, studied manuals up and down before committing. They never tell you if stuff turns into goo under some conditions. The question has been more of in-the-field experience.

[vladkri]

Good point about cure times. One month was between installation and splash.

[SVTatia]

Another thing to check is the expiration date inside the tube, at the bottom. They have relative short shelf life, and I cant find information on what happens after
it expires, I only know that some gets hard and some don't. I have many half tubes, all expired and unusable.

[Dockhead]

Originally Posted by GordMay

Sikaflex-291 is a non-sag 1-component polyurethane, which cures on exposure to atmospheric moisture.
Allow minimum of 1 week full cure prior to total water immersion situations. Avoid contact with alcohol and alcohol containing solvents during cure. [* under ‘Limitations’]
* ➥ https://productimageserver.com/liter...de/67311QG.pdf

Wow, this is new information for me.


We always threw the boat right into the water after installing something with Sika. Common boatyard practice.


Scary.

[Loredo]

Expired Sika 291 does not cure. I've tried to seal my mast base with expired 291, twas a mess! I noticed the expiration date only after having completed the job and thought time will tell. Several weeks later the Sika was still not cured...

[vladkri]

Originally Posted by Loredo

Expired Sika 291 does not cure. I've tried to seal my mast base with expired 291, twas a mess! I noticed the expiration date only after having completed the job and thought time will tell. Several weeks later the Sika was still not cured...

It's sure bad enough, but un-curing is on the whole new level of inconveniences

[s/v Jedi]

Originally Posted by vladkri

It's sure bad enough, but un-curing is on the whole new level of inconveniences

Are you sure it had cured before splashing?

[vladkri]

Originally Posted by s/v Jedi

Are you sure it had cured before splashing?

Yes. There is one more thruhull on the other side installed at the same time. Looks OK. The one in question is galley drain and another one close by.

[Bill Seal]

Food grease from the galley?

[vladkri]

Originally Posted by Bill Seal

Food grease from the galley?

This is crazy. From Sika-291 data sheet: "temporarily resistant to
fuels, mineral oils, vegetable and animal fats and oils; "
What in the blazes is that supposed to mean?

[africanmarco]

I recently had a similar experience with Sika 292. Had a sea water leak from the bow thruster tunnel last summer so took the boat out of the water (in Greece) and removed the bow thruster and cleaned well. A boatyard technician applied an abundant amount of Sika 292 (a new container, not expired) on the bow thruster flange and reinstalled it. The boat stayed on the dry for the entire winter. When I went back to the boatyard last April, noticed that on the inside of the boat, around the tunnel, the Sika had cured while on the outside (inside the tunnel) it was soft, sticky, gooey. Asking to fibreglass technicians around, I was told that now and then it happens and better to redo the job, which I did, using Sika 291, with a successful curing.

[Sailshabby]

It’ll fail eventually, I suppose. Probably good for temporary fixes?