Plastic thruhull and Sika-291i

[vladkri]

If I use Sika-291i to install Tru-design thruhull + ball valve on FG below water do I need to pre-treat surface with one of their aktivators? If yes, which one? They don't really say anywhere. Neither Tru-design, even though sika-291i is on their recommended sealant list. Thanks.

[GordMay]

It seems as though Sikaflex 449 primer might improve bonding of plastic to fiberglass.

“... SIKAFLEX® 291i Marine Sealant. A one-part polyurethane adhesive/sealant. Starts to cure (tack-free)
in approx. 2 hours, after which ball valves and or hoses can be attached. Full cure takes 24 hours – refer to manufacturer’s product literature...”
➥ https://trudesignplastics-com.s3.ama...e99ba29f86.pdf

Sikaflex®-291i Product Data Sheet
“... Method of Application
Surface preparation
Surfaces must be clean, dry and free from grease, oil and dust. The
adhesion of the sealant can be improved by wiping the joint with an appropriate Sika® activating agent and Sika® Primer if required.
Advice on specific applications is available from the Technical Service Department of Sika Industry.
➥ https://www.gaelforcemarine.co.uk/Im...20291iCure.pdf

Sikaflex® Sealant/Adhesive Primers
➥ https://usa.sika.com/content/dam/dms...Primers-us.pdf

[GordMay]

SIKA PRE-TREATMENT CHART
FOR SEALING AND BONDING IN MARINE APPLICATIONS
➥ https://industry.sika.com/dms/getdoc...t_Marine_e.pdf

[Training Wheels]

I installed all of our Tru-design thruhulls using Sika and no primer or activator and have had no issues.

[vladkri]

Thanks everyone. I could not find most of the above Sika tech notes.

[Fore and Aft]

vladkri I think you are over thinking it. The main requirement is to use plenty of Sikaflex when you are installing the thru hull. Then check it for leaks once launched.
I have used plenty of marine Sikaflex on skin fittings and never had a problem.
Cheers

[Franziska]

Think about it. The Sika gets compressed between the two flanges of the throughhull and the hull material. Where would it go? Just a clean, maybe lightly abraded surface is all you need. No primer necessary. We have all out through hulls installed like that. No issues.

A primer is definitely highly recommended if you use Sika to bond stuff together. For example, are windows glued in or teak deck seams.
In both cases, there are no mechanical fasteners holding the sika in place.

[Fore and Aft]

Good point Franziska. I also like to put the seacock on the skin fitting before tightening the thru hull nut. That way you can position the seacock handle correctly then tighten skin fitting.
Cheers

[s/v Jedi]

Originally Posted by Fore and Aft

Good point Franziska. I also like to put the seacock on the skin fitting before tightening the thru hull nut. That way you can position the seacock handle correctly then tighten skin fitting.
Cheers

That is impossible. You can’t have a seacock and a thru hull nut simultaneously.

I think you are installing a thru-hull fitting with a ball valve on top. Not recommended and ABYC does not allow it unless it’s up to a rather large diameter, because it’s too weak otherwise.

[Matt Johnson]

Tru design has both a thru hull nut and an overlapping seacock. Not sure how both go on at the same time, but they do have both items

[s/v Jedi]

Originally Posted by Matt Johnson

Tru design has both a thru hull nut and an overlapping seacock. Not sure how both go on at the same time, but they do have both items

They have a flanged collar and when you add that, you create the equivalent of a flanged seacock. I find the Tru Design top of the line but I have no direct experience with it. For boats in the US, Forespar has some good products in plastic (like this one: https://defender.com/en_us/forespar-...room-thru-hull) and in bronze or stainless steel, the Groco flanged adapter is very good: https://defender.com/en_us/groco-ibv...langed-adapter

[Fore and Aft]

I knew once I posted that people wouldn't understand. You put the skin fitting through the hull, then put on the skin fitting nut, hand tighten, then put on the seacock ball valve tightly by hand. Then rotate the seacock to the desired handle position and tighten the skin fitting nut which is below the seacock. Thats the short version minus the backing plate. Otherwise, when you tighten the seacock on the thru hull thread after the sealant has dried you can't control the location of the handle. Thats just me, I like to wind the seacock right down the thru hull fitting thread until it stops. Some people back the seacock off to the right handle position.
Cheers

[Franziska]

Originally Posted by s/v Jedi

That is impossible. You can’t have a seacock and a thru hull nut simultaneously.



I think you are installing a thru-hull fitting with a ball valve on top. Not recommended and ABYC does not allow it unless it’s up to a rather large diameter, because it’s too weak otherwise.

I'm in Europe and could not care less about ABYC [emoji2957]

[Pete7]

Originally Posted by Franziska

I'm in Europe and could not care less about ABYC [emoji2957]

Absolutely, what's more they are only an advisory organisation for one country on the planet. Nor do I agree with their advice, which is just what it is.

Watched a couple of YT videos a while back on gas installations. The viewers comments really tore into the ABYC.

There are tens of thousands of yachts with mushroom through hulls and ball valves referred to as seacocks if you like, doing sterling service as are ours. Glued in with a good seal of sika

[s/v Jedi]

It’s why EU regulated yachts sink due to seacock problems. It’s pretty easy to buy the TruDesign kit with the collar and be safe. Just a couple Euro’s.