Best Bedding Sealant?

[irwinsailor]

I am replacing all the plexiglass windows in the boat. I want 6to use a black sealent. I thought 3M 4000 uv would be a good choice but it does not come in black. I have been reading what I can about different products and I have been reading that using something strong is best. So I'm starting to think that using 3M 5200 or Sikaflex 295 are the way to go. I have heard that a very strong bond is not good if you want to change the window. So does anyone have any advise? Thanks

[Alan Wheeler]

I have just gone through this. I was told by the window experts to stay right away from Sikaflex. They told me to use a product called Silaflex, which is an MS Silicon product. MS=Modified Silicon. I have never been a fan of Silicon and so against their advice, I actually used another product Kinda similar to Sika, but made by the "Gorilla glue" people. It is a co-poloymer urathane adheasive sealant and seems to have done the job well. (so far)

[By Invitation]

Hey Gunner,

Just my 2 cents - I'm a fan of 5200, the stuff has never let me down. I'm installing all my windows ( 9 of them) this next week and it's 5200 for me. I'm never doing this again. I have a few tricks to work with the stuff if you want to know them, just ask.

Just a note, if I were planning on doing it again sometime I would stay away from 5200.

Scott

[Rick]

Wheeler is correct about silicones yet not about Sikaflex, which makes many other marine and industrial adhesives.

The proper way to bed and adhere to plexiglas is NOT to use 5200 directly. The proper manner is to use a plexiglass primer (which prevents the adhesive from crazing the plexiglass over time...all of the "standard" marine adhesives will attack Plexiglass with the exception of silicones which DO NOT adhere very well to plexiglass and leave a nasty residue that prevents good adhesives from adhering.

Next the adhesive is applied...see the Sikiflex web site for the correct primer and adhesive. Once the adhesive is applied and the job is essentially done you can apply a silicon sealer merely to obtain an nice finishing bead...do NOT allow the silicon to touch anything other than the adhesive that you are covering. Mose adhesives do not "finish" with a nice bead like silicione...which is none reason why silicones are used so ubiquitously and erroneously.

A similar technique is used to bed stainless steel...a primer is first applied, otherwise there is no reason to expect proper adhesion.

I have done these things and had many years of plexiglass and stainless steel sealings with good results. Merely follow the industrial experts who know their chemistry and avoid the usual marine buddy rumor mill like you see here.

Regards,
Rick

[irwinsailor]

I spent an hour on the phone with a a guy who is supost to know a lot about sealants. He said that the Sikaflex system was the best and told me to call the company rep. I did call sika and was impressed with what they told me. This repair is a much bigger deal than I ever thought it would be. I think that I will do the Sika and not use any fasteners on the windows at all. They tell me that it will be safe and i will not have any trouble.

[By Invitation]

Rick and Gunner,

My appologies for suggesting 5200 on Plexi, I miss read Gunners post and I thought we were talking about stainless frames. I did not mean to mislead anyone.

[irwinsailor]

I am replacing the windows and have been using the Sikaflex system. It looks Wonderful! Not having any screws makes for a great clean look. I have called the company 800# 3 times so far and have come away each time with what I needed to know. I am very happy.

[irwinsailor]

All done, very happy. Sikaflex it great.

[seafox]

Hi irwinsailor

did you use a dam rubber to space the window out 5mm from the boat?
How long did it take for the sika to hold the windows without any support?
cheers
Seafox

[irwinsailor]

I used a few plastic blocks to hold the window in position. Then I used plungers to hold the window tight to the boat for 24 hours. Then I back filled the gap with sika around the window to form a gasket. It was a fair amount of work but very much worth doing. Sika has a web site that has instructions and a phone number to a rep. I called them 3 times, they know what they are talking about.

[Talbot]

Make sure you get the correct grade of sikaflex for this task. There isone specially designed for it, with appropriate UV protection.

[irwinsailor]

It should not be a problem selection the correct product, they are clearly described on the web site.

[seafox]

I have bought some one adhesive sided 5mm x 9mm dam rubber. It is sticky on one side and comes in a roll. It is the hard closed cell pvc black rubber. I am going to stick this around the window opening on the boat to form a 5mm spacer between the window and the boat. It will also form a dam so the sika 295uv wont ooze into the boat when I press the window in. I will mask the exterior of the boat so that I can tool what oozes outside the boat. I was going to use chocks and duct tape to hold the window in position while the sika drys. There is a primer sika sells for the perspex window. I have bought some of that (very expensive) and will use it on the window first. Not looking forward to the job.

[Rick]

If the adhesive contact surface area is much wider than 3/8 inch it becomes increasingly difficult to prevent air bubbles from being trapped between the glass and the adhesive.


Does anyone have advice on just how to keep that from happening?

[GordMay]

BEFORE trimming the end and piercing the foil seal on the caulk/sealant tube, insert the cartridge in the gun, pump the trigger on the gun (to pressurize it). This will force out any air bubbles trapped between the plunger and the liquid. Air bubbles are more than a nuisance, because they continue to expand after you release the plunger pressure, and begin to lay your bead. RELEASE the plunger pressure, and trim off the end of the nozzle at a 45 degree angle, about the same diameter as your intended bead. Puncture the inner foil sealer (straightened wire coat hanger).
Begin applying your bead*, by caulking in one straight continuous stream, of about 2 Ft sweeps . Avoid stops and starts, as far as practicable. Force* the sealant deep into the joint, allowing it to slightly expand/flow outwards (*sealants don’t flow well).
Check back as you go, pricking any bubbles that appear and tooling** as required.

* You can either push or pull the tube, whichever is most comfortable for you - but it’s best to apply a bead by “pushing” on wider joints. By pushing the gun away from you, you are forcing the material into the joint. If you pull the gun toward you, you will trap air and produce air bubbles in the joint. It takes practice to lay down a perfect bead - practice first, on scrap or newspaper.

** Tooling can be done with a finger moistened with very slightly soapy water (wear surgical gloves if using solvent), or with a tooling trowel, a spoon, a shaped piece of wood etc. Clean your tooling implement after each use. It is important force sealant into the joint, and to avoid scraping an excessive amount of caulk out of the joint during tooling (to avoid starving the joint). If masking tape is used along the sides of the joint, make sure the tape is removed immediately after tooling is complete before the caulk skins over, so that it will pull away cleanly and leave a smooth, even line.