Trojan Boat Forum

I am replacing the backing plates on the through hull supports on my rudders and shaft struts . Somebody used plywood and of coarse it didn't last. I am using teak and was wondering if I should seal down with silicone or is there something better to use? Thanks, C. Don

Oak would be my choice on te wood and use 3M 4200 or 5200 , Do not use silicone below the water line !!

repete DO NOT use silicone below the water line

Thanks, Paul. I guess I would have used the silicone, glad I ask. I'll get the 3M and seal her down. C. Don

If you read the lable on marine silicone it will say not to use it be low the water line , the 5200 and 4200 say its ok , some" boat life" sealant is ok also (read the label ) west marine also has a store brand (9200? ) thats ok ,

There is also 3M 4000 heard good things but have not used it my self .

I did mine two year ago and used "BoatLife Caulk" never any leaks, 4200 would work also do not use 5200 if you ever want to get it off again, it is for a permanent repair. I also used "BoatLife Caulk" this year when replacing my splash rails it hold us very well.

I'm in the silicone business, have been for over 30 years. DON'T EVER USE IT BELOW THE WATERLINE! Silicone wants to migrate AWAY from water and it will not adhere to anything wet. When we caulk windows we "spit tool" the caulk for a smooth line - basically lick the tip of your finger and use it for a smoothing tool. 3M 4200, etc and/or any polyurethane sealant is the way to go. When you use the sealant don't tighten down on the backing plate all the way. Let it cure up a bit and then tighten down. If you tighten down too soon you can squeeze the sealant out.

Once again Randy this is very valuable information. Thanks for the tip on not tightening down too. Don

NO silicone!

5200 is the right choice - and you can remove it if you have to (but I assume you want it to really adhere and be "sealed". which it does wonderfully.

5200 does not shrink, and another bonus with 5200 is that moisture is what sets it up. If you apply it under water, it will firm up in less than an hour! If you apply it above, it will take at least 6-8 hours to firm up, 24 hours to harden and 5 days t- cure completely.

3M 5200 is one of the stickiest substances on earth, so have plenty of paper towels, some lacquer thinner and a bucket for trash when you apply it! The 1/2 width towels work great (Scott?), as you will go through a lot of thm, and the big towels get wasted.

You can buy 3M 5200 in:

• * Slow or Fast cure
  * White, Black, Brown or Tan
  * 10oz Caulk Gun Cartridge or 3oz Squeeze Tube

I have worked at removing 5200 before and short of mechanically removing it- it will remain. The 4200 works just as well and you never know when and for what reason it may need to be removed. Always prepare for the unknown. When I replaced my rudder backing plates I looked at 5200 and was advised not to use in the application by a marina owner unless I was 100% sure I never wanted it off.

Thanks Dan, I'll go with the 4200 Don

I spent 3 days chiseling, trying to separate 5200 from a Hatteras flybridge surround...

Don't use 5200 if you even think you'll have to remove the piece you're securing, in the future!

I ended up using 5200 for re-doing my strut mounts (backer boards got dry rot) and thru hull fittings (hope I dont need to remove ever) and the one thing I have to say is that stuff is pure magic

I spent a few days with bedding all the underwater components, and it seemed that every time I turned around there was a white print resembling a portion of my anatomy stuck to something. There was a big toe print on my car floor mat, thumb print on dogs head, forehead prints dotting the hull from the intakes to the rudder logs, even finger prints on my wifes bottom side that my daughter pointed out..........that ended up on the leather seat of her car......

I am telling you that 5200 stuff is magic the way it gets around.

MAC - very funny! I have had the same experience.

5200 is possessed ... it will go EVERYWHERE - but it WILL stick and seal forever! You can remove it with a sharp knife.

I couldn't even get it off with a razor blade. Look under the 3M link the 4200
3Mâ„¢ Marine Fast Cure 4200 Adhesive Sealant
One part general purpose polyurethane reacts chemically with moisture for flexible bonds to wood, fiberglass, gelcoat, plastic and metals. Forms a watertight seal on joints and boat hardware above and below the waterline. Formulated to allow for disassembly of parts.

The 5200 is made for structural movement, the bonding of this stuff is unbelieveable