2-pack polyurethane over traditional varnish

[nickj]

Hi all,

I have a lot of brightwork to manage and I'm considering putting a 2-pack polyurethane layer over the top of the traditional varnish for longevity. A product like this:

https://www.norglass.com.au/products...northane-clear

It's unclear to me why this isn't completely standard practice. So, I'm wondering what the reason for that is, before I commit...

If I do commit, would a yearly top layer of polyurethane keep everything in Bristol shape? The varnish base is at around 5 coats.

Nick

[capt jgw]

Not sure about varnish, but with paint the 2 pack type will bubble and lift 1 pack paint. The solvents are too aggressive. You'll likely have to remove to bare wood before applying the new product. Clear epoxy makes a good base for this, has better fill and is cheaper allowing fewer coats of the 2 part varnish.

[Jammer]

Originally Posted by nickj

Hi all,

I have a lot of brightwork to manage and I'm considering putting a 2-pack polyurethane layer over the top of the traditional varnish for longevity. A product like this:

https://www.norglass.com.au/products...northane-clear

It's unclear to me why this isn't completely standard practice. So, I'm wondering what the reason for that is, before I commit...

If I do commit, would a yearly top layer of polyurethane keep everything in Bristol shape? The varnish base is at around 5 coats.

Nick

What jgw said. The solvent system in 2-pack poly is aggressive enough to dissolve and blister the trad varnish. With that particular product it's the xylene and ethyl benzine content.

[wingssail]

"It is known that polyurethane used for both interior and exterior applications are subject to photo-degradation when exposed to ultraviolet light. Photo-degradation is a process whereby the polymer chains in the product break down due to exposure to UV radiation. The UV light, which makes up about 10% of sunlight, is electromagnetic radiation with a wavelength shorter than visible light but longer than x-rays." https://mitchellfauxleathers.com/Def...inyl-materials

To me, this means that your 2 part Poly will still degrade if exposed to sunlight. Best to strip everything off the wood first, and renew the poly when it starts to go bad.

There is mention of adding UV protective chemistry to the poly. Still I'd strip the wood first.

[NevilleCat]

Have a chat directly to Norglass.

[Franziska]

Originally Posted by Jammer

What jgw said. The solvent system in 2-pack poly is aggressive enough to dissolve and blister the trad varnish. With that particular product it's the xylene and ethyl benzine content.

On top, 2K has different flexing characteristics then 1K.
Which leads to flaking too.

2k on top of 1k is never good. The other way around it may work.

All materials suffer from UV degradation.

2k usually less than 1k.

Clear epoxy needs therefore always a PU varnish on top, otherwise it yellows pretty fast.

[mickand]

I've been refinishing boats professionally in Florida for 20 years. Early on I was continually embarrassed at the short life of varnish in that harsh environment.
I've been applying one topcoat of 3 part Awlbrite over the varnish layer for over 15 years and it's fully compatible.
Poly has little UV so build up first with marine varnish.
I consider Epifanes to have the best UV protection.
The Awlbrite protects the varnish layer much as Clearcoat does on a car.
You can also easily repair Awlbtite.
Expect up to 4x life.

[Thumbs Up]

Awlbrite is specifically formulated to use over tung oil based (traditional) varnish systems.
Northane clear is not and will probably attack the varnish.

[picklesandjesse]

I've had a couple of varnished hulled boats and used awlbrite or Sterling over traditional varnishes with no problem. You have to make sure the traditional varnish is well cured. They recommend 3 months. You'll get and much longer lasting finish and better gloss too. Goes on very thin and flows into itself in an amazing way. Bit of a learning curve though. Read application instructions and believe them. Good luck. You can buy it in Aust. Distributer is in Gold Coast. Avail in Sydney near Fivedock from memory.

[garyfdl]

I'm 'old school'... was always told not to put anything over varnish, or varnish over anything (but bare wood).

For the last 40 years I have always oiled my teak (Deks Olje). It isn't as shiny, and tends to darken the teak with time, but is a helluv'a lot less work.

[CarinaPDX]

Consider going a different way: use Cetol instead. It is very durable, is very easy to overcoat (no sanding required), and is very easy to repair. A lot of cruisers mis-used Cetol and complain of an orange look. The proper way to use it is to apply the regular pigmented ("natural" or "teak" or whatever) in two layers over bare wood, and then overcoat with multiple layers of clear. Annual maintenance is to clean and apply two layers of clear on top. Easy.

The problem with 2-part coatings is that when they have to be removed - and they will at some point - they are a nightmare to sand off as they are very hard.

Greg

[adjo]

I'm surprised no one has mentioned Coelan.
It's expensive but reportedly pays for itself through longevity.
I've never used it myself but have inspected a couple of boats where it has been used and the owners were very impressed.
I would be interested in hearing from someone who has personal experience.
Good or bad.

[jmschmidt]

I wouldn’t waste the time, money of nuisance of using 2-part poly on interior bright work.
Exterior for bear teak I lay down a first coat of highly thinned (30%) epoxy resin, sand smooth add and second coat of the same thinned to only 10%, re-sand to smooth. This provides an excellent base for any kind of varnish, one part or two. My four coats of two-part finish have lasted ten years on exterior grab rails which are kept under cover.

[Bowdrie]

For ~40 years I've been using Smiths CPES as the base coat on bare wood before varnish.
Thinning down epoxy is mostly hit-an-miss, no matter what you thin epoxy with, it still has a short pot-life, and will seldom, if ever, penetrate deeper than the first layer of un-broken cell structures in the wood.
The "plastic" 2-part stuff looks great,, for awhile, but it will require work to maintain it, and as a previous post stated, it's a @*^$* to get off.
Cetol,, it's for heretics,,
The old way of applying varnish, using several coats, with the first massively thinned, and successive coats progressively using less thinner is akin to the old Hot Rod technique of 15 coats of primer,, but you sanded off 10 of them before the Candy Apple Red went on still works,, but why.
But I gotta agree, varnish, no matter how you use it, is a real job.
It's one of those things you have to have a passion for,, that's one of the reasons to have a Hinckley.

[wingssail]

Originally Posted by Bowdrie

...But I gotta agree, varnish, no matter how you use it, is a real job.
It's one of those things you have to have a passion for,, that's one of the reasons to have a Hinckley.

I'd love to have a perfectly looking boat: perfect varnish on the wood trim, perfect paint, perfect stainless, and every line end whipped, all the canvass clean and no worn spots...the list is endless.

I could do it, too.

But I also need to have a perfectly functioning race boat. We need to be able to sail and sail smoothly and efficiently with every block running easy, with all the lines repaired, with every sail and sail handling piece of equipment good, even perfect.

As much as I like a nice looking boat, my passion is not looks, it is sailing.

And unless I can afford some professional help (which I can't), something has to give.

In my case, I put it all on the project plan, but the sailing stuff goes to the top. And if I don't get to the bottom of the list, so be it. At least the high priority items will be done and when the crew arrive on race day, we will be ready.

The best looking boats in this harbor never go out.