3M 5200 Sealant

[straycat]

I have used 3M 5200 for many non reef projects like marine boats & motors, etc. It is the best underwater sealer I have ever used. Question it is Mildew resistant and I know that many think it's a no no in reef tanks, sumps, fittings etc.. Has this really been proven to be a problem in this hobby? Thanks

 

[uncleof6]

No, it is not a proven problem. What is proven is uncured silicone is a problem, along with just about any uncured product. Is polyurethane with a mildew inhibitor harmful? Depends on if there is actually a mildew inhibitor in the "mix," where as in silicone there is no indication that such an additive is present, despite the advertising.

My question would be: what is the intended usage?

What is recommended for aquarium use is:

1-Part
Acetoxy Cure
100% silicone (no co-polymers in it)
FDA approved for food contact.
Appropriate for the purpose: sealants for sealing, adhesives for structural uses.

That said, polyurethane does bond to glass, in a manner similar to silicone. However, when looking at the data sheet for this particular product, we see some things that could be unsettling:

"- 3MTM Marine Adhesive/Sealant Fast Cure 5200 is not recommended for the installation of glass, polycarbonate or acrylic windows that are not also mechanically fastened with a system designed by the manufacturer. Inconsistent adhesion of these unprimed substrates, specific design of the window and movement due to thermal expansion and flexing, may cause application failure."

So first we see that "aquarium" is outside the appropriate usage for this product. Secondly, we are not using windows, rather large chunks of plate glass, that in some cases are not mechanically fastened, and are subject to movement due to thermal expansion and flexing. I have also "read" (outside the hobby) of "some" cohesive issues with polyurethane adhesives, though the bond to glass is suitable. It is older information, so take it for what it is worth, as I can't give you the specifics.

Fair is fair, so what is your intended usage in the tank? I am not going to sit here and say "don't," without knowing what you have in mind. Though there may not be any chemical ramifications, there could possibly be some others. Myself, I would use something that is known not to have these additional "complications." See above recommendation.

http://multimedia.3m.com/mws/mediaw...UqevTSevTSevTSeSSSSSS--&fn=Fast Cure 5200.pdf

 

[straycat]

It's time consuming answering questions I know so first off thanks!
Will be building an all glass sump/refum, etc. starting with a new glass breeder tank, just adding glass baffles and such.
Thanks for the link, if I had of read it before I would not have had to ask the question! Thanks again...........................................................

 

[uncleof6]

It's time consuming answering questions I know so first off thanks!
Will be building an all glass sump/refum, etc. starting with a new glass breeder tank, just adding glass baffles and such.
Thanks for the link, if I had of read it before I would not have had to ask the question! Thanks again...........................................................

Don't use it Use Momentive RTV108--please.

 

[hk855]

I've used it before for sealing bulkheads on not flat surfaces but not much else. Basicaly using it as a gasket that fits to imperfect surfaces, also for sealing aluminum contacting water in a few scenarios. It works well and haven't seen it hurt things but it's a small contact surface on a very big water volume. I wouldn't use it for building sump baffles or as a standard plumbing product. Pretty much only for sealing a bulkhead with a bad gasket or surface or similar small leak issue. It takes forever to dry and would take 2 days if used in typical silicone manner on baffles for example.