Comparison of retail marine sealants for bedding deck fittings

[demonboy]

Found this table quite useful in my research for bedding sealants, which I picked up from http://www.boatus.com/:

Obviously worth reading around the subject but serves as a useful crib sheet for those of us who don't know the difference between polysulfide and polyurethane.

 

[Durcott]

This is interesting - just how much attention should we be paying to the 'Incompatible with plastic' comment?

Jeff

 

[Poignard]

Does anyone know what category CT1 comes into? The manufacturer's product info just says it is a 'hybrid polymer'

 

[SimonD]

Butyl tape "can be difficult to obtain". Not on Ebay it isn't. Personally, I wouldn't use anything else to bed down deck fittings.

 

[doug748]

Butyl tape "can be difficult to obtain". Not on Ebay it isn't. Personally, I wouldn't use anything else to bed down deck fittings.

How do you use the tape? Do you overlap it and stick it down like pieces of double sided Sellotape?

I normally use Silicone for everything, but it can be a bit messy

I may try the tape under some stanchions this winter.

 

[chubby]

Does this list extend to bedding in windows to prevent leaks: I did mine with silicone sealant and guess what after a few years leak, the table explains why, at SIBS was given various advice but the more powerful sikaflex would be so strong as to prevent any future dismantling, so butyl seems the thing, what do folk think?

 

[SimonD]

How do you use the tape? Do you overlap it and stick it down like pieces of double sided Sellotape?

I normally use Silicone for everything, but it can be a bit messy

I may try the tape under some stanchions this winter.

That's exactly it. The individual pieces of tape tend to join together under pressure from the fitting. They then continue to creep over time. There's a very good article on the subject on pbase.com - google "sealing deck fittings with butyl tape" to find this and other tips.

 

[demonboy]

Butyl tape "can be difficult to obtain". Not on Ebay it isn't. Personally, I wouldn't use anything else to bed down deck fittings.

I used Arbormast BR for my last hatch job (it's a butyl based sealant). That's also difficult to obtain, mainly because the people at Arbo seem incapable of answering my emails to them! I have one tube left but am keen to get hold of more because it seems to be a sensible bedding solution where there is movement. I might have to look into getting some of that tape shipped over.

 

[Tradewinds]

That's exactly it. The individual pieces of tape tend to join together under pressure from the fitting. They then continue to creep over time. There's a very good article on the subject on pbase.com - google "sealing deck fittings with butyl tape" to find this and other tips.

Here's the article - excellent advice.

http://www.sailnet.com/forums/gear-maintenance/63554-bedding-deck-hardware-butyl-tape.html

 

[vyv_cox]

Very surprised to read that polyurethane has no chemical resistance, as it is widely used in some chemical industries. This chart gives plenty of detail https://www.spilltech.com/wcsstore/...ore/Attachment/documents/ccg/POLYURETHANE.pdf and suggests thst unless you are using some very strange substances on board you should be perfectly OK with it.

As for incompatible with plastic, are they in the same world as me? Almost everything on my plastic boat is sealed with one or other Sikaflex, or Puraflex 40, including plastic fittings. It is also the sealant of choice in caravan manufacture, also mostly plastic.

 

[capetown]

And Puraflex 40 is only £3.92 a cartridge

 

[BERT T]

Using Butyl Tape: https://www.youtube.com/watch?v=4Upksj19lyU

All points of this video ARE accurate but a very important point should be added. Being rubber based, as opposed to the "liquid" consistency of a caulk, BT has an extreme viscosity. This means that a proper bedding isn't achieved without returning to add slightly more torque to the bedded bolts. The process to fully bed BT MAY take 2-3 days, with 12-24 hours between tightenings. Full bedding is achieved when squeeze out no longer occurs. This extra labor is why few production boats use it.

 

[Boreades]

For the last sealing job, on a leaky stantion base, I used Screwfix Silicon.
£2.95 a tube.

 

[Javelin]

Butyl tape "can be difficult to obtain". Not on Ebay it isn't. Personally, I wouldn't use anything else to bed down deck fittings.

+1

 

[AngusMcDoon]

All points of this video ARE accurate but a very important point should be added. Being rubber based, as opposed to the "liquid" consistency of a caulk, BT has an extreme viscosity. This means that a proper bedding isn't achieved without returning to add slightly more torque to the bedded bolts. The process to fully bed BT MAY take 2-3 days, with 12-24 hours between tightenings. Full bedding is achieved when squeeze out no longer occurs. This extra labor is why few production boats use it.

Quorning who make Dragonfly trimarans use it extensively. It never seems to leak, and neither does it set. After 15 years getting a fitting off is dead easy, and the sealant can often be scraped off and reused.

 

[vyv_cox]

For the last sealing job, on a leaky stantion base, I used Screwfix Silicon.
£2.95 a tube.

I agree (almost) 100% with the table as regards silicone sealants. Definitely the worst choice you can make on a boat. Poor adhesion and poor strength unless professional grade stuff heat treated to cure. Worst of all is that it inhibits the cure of many other adhesives and sealants, so once used you are doomed! And it is very difficult to remove all traces.

 

[ghostlymoron]

I'm about to fit a NASA log skin fitting. I believe they recommend silicone sealant.

 

[vyv_cox]

I'm about to fit a NASA log skin fitting. I believe they recommend silicone sealant.

They do, because the one advantage of silicones over most other sealants is that they contain no solvents that might react with the plastic log fitting that NASA supply. I assume that they have had some adverse feedback about solvent based sealants but other makers who supply plastic fittings seem to have no problem with better sealants.

 

[demonboy]

After stressing about buying and shipping either Arbomast or butyl tape to Thailand (I'll be ready to bed my deck fittings next week) I tried explaining what butyl tape was to the yard manager. "I think I have some of that in my shop in town", he said. An hour later he produced this (pictured with my one spare tube of BR. Incidentally Martin Blunden of Arbo got in touch in the end. He was very helpful and am just waiting for him to come back with distributor details.):

What I need to know now is, how many layers of this stuff should I use for a deck hatch, with an aluminium rim 30mm wide? Should I build up two layers or is one enough?

 

[vyv_cox]

That looks just the same as the stuff I used to bed one of my wheelhouse windows on Cecilia. It is what Mainbrace in Milford Haven use for all similar sealing jobs. It has worked fine in excluding water but seems to continue extruding almost indefinitely. I used a single layer that seems perfectly adequate.