TruDesign through hull fitting instructions - why is a second tightening needed?

[nicholat]

Hi, We're in the process of researching the installation of Trudesign through hulls and seacocks. The Trudesign fitting instructions state that the through hull nut should initially only be tightened finger tight, followed by a second tightening to 15 ft lb after the sealant's curing time.

We're planning on using Sikaflex 591, which is on the list of Trudesign's recommended sealants. We've looked up the application guide for this Sikaflex product and can't find anything about doing a second tightening after the curing time. We've used Sikaflex 591 before with bronze through hulls and did not do a second tightening.

Does anyone have any insight as to why this second tightening is necessary? We're nervous that by doing a second tightening, we'll break the initial bond that the Sikaflex has made during its curing process.

Did others who have used the Trudesign products do a second tightening?

Thanks for any help you can provide and experiences from those who have fitted these types of through hulls.

 

[Graham376]

I think I used 291i and no second tightening, 8 or 9 years on and no leaks.

 

[Neeves]

You are applying a sealant not an adhesive. The second tightening compresses the sealant you applied allowing it to better seal (in the same way you compress a rubber gasket).

Whether you need to make the second tightening, I don't know, but I have usually tightened after the sealant has set off - without any issues. If you are using the sealant as an adhesive then there might be no sealant to compress.

I'm not sure about the 15ftlbs - sounds quite archaic - have they not metricated the recommendation . I just give the fitting a 'bit of a turn'

Jonathan

 

[wingcommander]

The risk is if you over tighten on application, you run the possibility of squeezing out most of your sealant. The flatter the faces the more the possibility. Hence the hand tighten and do up next day.

 

[VicS]

Hi, We're in the process of researching the installation of Trudesign through hulls and seacocks. The Trudesign fitting instructions state that the through hull nut should initially only be tightened finger tight, followed by a second tightening to 15 ft lb after the sealant's curing time.

We're planning on using Sikaflex 591, which is on the list of Trudesign's recommended sealants. We've looked up the application guide for this Sikaflex product and can't find anything about doing a second tightening after the curing time. We've used Sikaflex 591 before with bronze through hulls and did not do a second tightening.

Does anyone have any insight as to why this second tightening is necessary? We're nervous that by doing a second tightening, we'll break the initial bond that the Sikaflex has made during its curing process.

Did others who have used the Trudesign products do a second tightening?

Thanks for any help you can provide and experiences from those who have fitted these types of through hulls.

The instructions tell you to apply the adhesive sealant to the flange of the fitting and only a little way up the thread.
If done properly no sealant should get on to the nut or that far up the thread.
When the sealant has cured it should then be possible to tighten the nut as instructed without the fitting turning but it would be advisable, imho, to counter-hold the fitting .
Follow the instructions!

 

[Keith-i]

Interestingly I fitted True-design this year and followed the instructions. After the sealant cured I found it possible to give the nut an extra bit of a turn which won’t have done any harm. This was on a 2” bsp fitting. The smaller fittings on head didn’t seem to need it.

 

[dankilb]

You do it 45 mins after application so the sealant is still flexible enough (and I’d argue not fully ‘bonded’ yet but I’m no chemist) to compress without compromising the seal. It acts more as a gasket that way. It is widely used practice.

Not sure I’d second-tighten once the sealant had fully cured. It’s never occurred to me. If applied and installed ‘correctly’ it shouldn’t be necessary (nor possibly, I’d argue…). It could theoretically beak any mechanical bond between one or other mating surface. PolyU forms a good gasket anyway so second tightening after cure is probably harmless enough in practice.

 

[VicS]

You do it 45 mins after application so the sealant is still flexible enough (and I’d argue not fully ‘bonded’ yet but I’m no chemist) to compress without compromising the seal. It acts more as a gasket that way. It is widely used practice.

Not sure I’d second-tighten once the sealant had fully cured. It’s never occurred to me. If applied and installed ‘correctly’ it shouldn’t be necessary (nor possibly, I’d argue…). It could theoretically beak any mechanical bond between one or other mating surface. PolyU forms a good gasket anyway so second tightening after cure is probably harmless enough in practice.

The fitting instructions (qv) say to finger tighten initially then further tighten, to no more than 15 lbs.ft, when the sealant has cured.

 

[Neeves]

The fitting instructions (qv) say to finger tighten initially then further tighten, to no more than 15 lbs.ft, when the sealant has cured.

The sealant has to cure or you will not compress it. The hand tightening initially is to 'leave' some ability to tighten once the sealant has cured completely - if it was tight, tight you would be unable to compress it. You don't need any sealant on the thread, its not an adhesive, and you are going to break any adhesion when you give the final tighten - the 'seal' is produced by you compressing the cured sealant. If its a well matched thread any sealant on the thread would be squeezed out when you hand tighten.

This the same mechanism if you replace windows. If you apply sealant (not adhesive), screw the window down, allow sealant to set off - further tighten the screws, nuts and bolts, inter screws to compress the sealant. It depends on the thickness of sealant but there is the need to wait for it to fully cure (or you will squeeze it out and there will be no 'room' left to compress. Some windows are attached with adhesives (that look like sealant) - adhesive is then not compressed (there are no screws to allow compression). Sealants like a long time to set off, slowly (its a chemical reaction with water (usually atmospheric moisture) - keep out of the sun if possible to maximise strength.

Jonathan

I learnt all this when we replaced windows and the Australian manufacturer of the adhesive took time to explain to me over the phone and then summarised the procedures on a long and detailed email. Its why some companies have technical departments.

 

[Norman_E]

I think I used 291i and no second tightening, 8 or 9 years on and no leaks.

That should work just fine as Graham says, but when my through hulls were replaced with Tru Design and all new Tru design ball valves they were done with a different Sikaflex in a small tube. I cannot remember the number but it allowed the fittings to be moved to get them aligned correctly for some hours after initial set. We had no leaks and no problems.

 

[lustyd]

That should work just fine as Graham says, but when my through hulls were replaced with Tru Design and all new Tru design ball valves they were done with a different Sikaflex in a small tube. I cannot remember the number but it allowed the fittings to be moved to get them aligned correctly for some hours after initial set. We had no leaks and no problems.

The sealant for the valve to thru hull is different you probably used loctite 5331. This is a sealant and allows movement and breaking of the seal and is used instead of Teflon tape.
No idea why people keep saying Sika isn’t an adhesive, the one TruDesign recommend is an adhesive and there’s no way I’d want to disturb it after installing. I tightened mine when applied and then left it well alone.

 

[Neeves]

The sealant for the valve to thru hull is different you probably used loctite 5331. This is a sealant and allows movement and breaking of the seal and is used instead of Teflon tape.
No idea why people keep saying Sika isn’t an adhesive, the one TruDesign recommend is an adhesive and there’s no way I’d want to disturb it after installing. I tightened mine when applied and then left it well alone.

Many of the sealants are also an adhesive - which you find out when you want to remove the fixture.

In this case the material is being used as a sealant, as you would a gasket or rubber washer. The adhesive characteristics are not required.

As is shown many do not follow the instructions to 'crush' the cured sealant and develop a more robust seal and have no issues. Its up to the owner - its his responsibility.

Frankly giving a fitting an extra half turn once the sealant has cured hardly seems onerous.

Jonathan

 

[lustyd]

Frankly giving a fitting an extra half turn once the sealant has cured hardly seems onerous

Not onerous at all but does risk breaking the perfectly good seal that’s in place. I can see the wisdom in it 30 years ago when adhesives and sealants were not what they are today but it’s no longer necessary in my opinion, especially with fittings like TruDesign that are almost impossible to hold still to tighten even with the special tool.

 

[Neeves]

Not onerous at all but does risk breaking the perfectly good seal that’s in place. I can see the wisdom in it 30 years ago when adhesives and sealants were not what they are today but it’s no longer necessary in my opinion, especially with fittings like TruDesign that are almost impossible to hold still to tighten even with the special tool.

Actually - though I follow the instructions the whole concept is flawed.

The recommendation comes from Tru-Design and I assume they have passed it by the sealant manufacturers.

The initial tightening is 'hand tight' and my hand tight - a wimp with small hands - will then be different to those who use their hands a lot. The final recommendation is to tighten to 15ftlbs.....? I do have a torque wrench but its for a bicycle, not a thru hull fitting (hands up anyone who has a large enough torque wrench - I know there will now be a whole cricket team) - but why not the metric equivalent.

Jonathan

 

[nicholat]

I think I used 291i and no second tightening, 8 or 9 years on and no leaks.

That's great to hear, 9 years and no leaks is a very good endorsement for the product

 

[Copious]

Contact dslittle on YBW forums who has just fitted about 10 of these.