Sealing thru-hulls

[rajjes]

I’m replacing a thru-hull and am planning to use sikaflex as sealer.

I understand that rather than tightening it up fully immediately, it would be better to tighten it gently, leave the sealer to set and then tighten further.

Could you confirm that this is so? Also, should I use the sealer only on the outside and some of the lower threads, or also under the securing nut? (If so would it set too hard to allow further tightening?)

Apologies for these basic questions but I guess its better to double check as its below the water line!

 

[Evadne]

Like they say, there's no such thing as a dumb question. By letting it set then tightening up you are using it as a sort of o-ring or gasket, tightening up immediately will squeeze most of the sikaflex back out again. So yes, let it set and yes, only on the outer face, that is not being rotated. If you must seal under the nut, do so after the outer has set, then tighten immediately, but don't expect it to come off easily next time. Or at all. /forums/images/graemlins/blush.gif

 

[oldsaltoz]

What is the fitting made of, some types of plastic react to Sikaflex sealant depending the type you plan to use.

Other than that. Clean the area and seal the outside only and around the exposed edge of the cut hole, tighten by hand, wipe any excess away with a damp cloth inside and out. Leave for 24 hrs and finish tightening.

Andavagoodweekend......

 

[cliffordpope]

I read that it is important not to fill the narrow space between the transducer and the sides of the fairing piece , otherwise it dampens the signal.

 

[timtap]

Having built literally hundreds of boats I fit the thru-hull fittings with Sikaflex (both sides) and tighten them up . coming back to them later is not a option when manafacturing boats on a production line basis.
I must add that in recent times we used a product we called 50/50 which is a two product putty type substance that when mixed together goes off like rubber after 24 hours. this is used for all skin fittings and applied like putty both sides of the fitting again and tightened up, the excess can be cleaned off immediately and cleanly.

 

[lw395]

If you re-tighten the thru-hulls you are likely to break the seal imho. If you put a small chamfer on the outside edge of the hole, this retains a ring of sealant, even when the fitting is done up firmly. IMHO, you are right not to want to squeeze all the sealant out, but I think its better to get the sealant into a controlled space such as a chamfer or grooves under the head of the skin fitting.

 

[Chris_Robb]

Do you need to seal the laminate in a newly cut hole? - what would you do this with? an epoxy filler?

 

[oldsaltoz]

Yes you MUST seal the raw glass to prevent moisture getting into the laminate.

Make sure it is very clean and dry, then apply 2 or more coats wet on tacky to avoid sanding between coats.

 

[Refueler]

Yes Laminate should be sealed with epoxy ... even araldite / other rapid is better than nothing.

Sikaflex is not so easy to find out here in baltic - so good quality exterior silicon sealant is the norm.
Good squirt round under exterior lip and enough to make sure any void areas through hull are filled, wind on nut and do up well but only by hand. It shouldn't need at any time a spanner ... apart from maybe a very small nip maybe a 1/4 turn max.
Some people have used grips on them and wonder why the outer lip fractures and eventually falls of !

 

[tabernacleman]

My policy has always been to apply in and out and according to the fitting instructions with my last job (with Raymarine transducers) apply sealant up past the threads for 15mm so the retaining nut squeezes the sealant onto the inner hull,(which should of course be smooth and clean. Then after a few hours nip it up. I query the need to seal the inside walls of any hole cut with hole cutter in a solid glass hull,(pretty snug fit if right hole cutter used) /forums/images/graemlins/frown.gif the sealant should keep out any water, in a balsa core deck/hull then obviously there is a recognised need to ensure water does not get anywhere near the balsa ( my snowgoose is a prime example of this principal not being followed) much gouging of rotten balsa needed between the sheets so to speak, when refitting windlass and other deck fittings, before pouring in epoxy. So easy to do the job properly in the first place, (compared to the fixing of a bad job) I wonder why people just drill and screw.

 

[tabernacleman]

re 'oldsaltsoz' comment re some plastics reacting, can you specify which manufacturers through hull fittings react, rather important that we all know this!!!

 

[Refueler]

unfortunately if you go to a builders - I used to oversee various builds in past years - it's not unusual for voids to appear in laminates ... dry laminate where resin hasn't penetrated ... lots of reasons that playing safe by sealing the cut egde.

Agreed that theoretically it's not needed. Practically though - yes it is.