To bolt or not to bolt that is the question

[Casagf66]

After much thought and after reading everyone's post's 100's of times, over and over ... I've decided to go ahead and lay out the big bucks on the sika products for rebedding my sky lights. My plan is to eliminate the ugly aluminum surface framing, sex bolt design and instead surface mount the port lights. I'll be using the original (lexan I think that's what it is how can you tell the difference ?), infilling the holes on the lexan with smooth black barrels and purchased 3M adhesive tape to hold the lights in place while the sika dries. Am I making a horrible mistake or will this work?

Do surface lights need bolts and or screws?

Here are some pics of the lights on and off.. they definitely needed reconditioning

 

[Brian S]

According to that Sail magazine article, the 3M acrylic tape and Dow Corning 795 structural adhesive should hold just fine. Even though you say you aren't planning on the 795. By the way, they use the 795 to glue window panes onto buildings. (Pretty sure you've seen links to the article from your other posts.)

I found that my leaks were caused not by a failure of the silicone sealant, but rather spider cracking from the fastener holes where the screws held the window on. The cracks migrated under the area that was sealed, to exposed gelcoat, and water would drip in through the crack under the sealant. Factory builders don't seem to countersink pilot holes drilled into fiberglass, which leads to spider cracks and failed sealant bonds. Removing my old, crazed portlights was difficult as I had to cut the sealant. No evidence of sealant failure at all.

 

[Casagf66]

Brian,
The link you posted on my previous discussion is what got me thinking a surface mount aplication would be beter. When removing the lights I too noticed that the window failed at the sex bolts and not at the adhesive. This is why I am leaning towards a surface mount application.

I'm just concerned that without the bolts it may not be at strong.

Thank you

 

[agprice22]

Here is the thing... The 795 will separate when the bead is small. My "portlights" on my 272 were glued down with 795 two seasons ago, and they need to be resealed at the outer edge. The problem is that the plexi expands and contracts at a different rate than the fiberglass deck, so the 795 gets pulled between them. Yes, 795 is designed for structural but needs, but I think it separates when applied in thinly. If the bead is thick and wide, 1/2 inch to 1 inch, it may hold up, like it does in buildings. It may work, and I think it is an improvement over the recessed skylights you currently have, which invite water to intrude, but check it often.
Also, could you used a bead of Butyl Rubber around the outside of the plexi?

 

[agprice22]

Oh... However, once you secure with the 795, the screws are superfluous... In a skylight application, I admit I would use them, but I over engineer everything...

 

[Ralph Johnstone]

Take a look here if you haven't yet:
http://forums.sailboatowners.com/index.php?threads/fixing-seal-on-sailboat-windows.176961/
I was impressed by the Boatworks Today video posted by Nick. After seeing this, I'm inclined to think that using 3M VHB tape as the adhesive and 795 as the sealant is a superior method of installation compared to how my ports were originally installed by Hunter using only 795.

 

[Brian S]

As for differing thermal expansion rates, the Sail article is pretty specific about which thickness VHB tape that you use to accommodate thermal expansion. I feel that the VHB tape provides the mechanical join, and the 795 a secondary adhesion and primarily sealing.

Of course, make sure after you remove all the previous sealant, to sand the gelcoat to remove all the contaminated area. Silicone contamination prevents even new silicone from adhering! I've got a Beckson deck plate on order so I can replace rudder bolts on my Force 5. It really chaps me that Beckson says to use only silicone to seal the flange. To paraphrase Indiana Jones, "Why's it gotta be silicone?!?"

 

[Ralph Johnstone]

As for differing thermal expansion rates, the Sail article is pretty specific about which thickness VHB tape that you use to accommodate thermal expansion.

Brian S,
Do you have a link to the "Sail" article you refer to ? Thanks.

 

[Casagf66]

http://www.sailmagazine.com/boatworks/replacing-fixed-portlights

I think this is the article Brian is referancing

 

[Brian S]

Yup, that's the one.