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Old 10-07-2020, 14:18   #1
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Two or one part paint?

I have been a long time fan of two part epoxy and polyurethane paints and we have used them exclusively on our steel Gazelle. On a previous wooden sloop that we owned prior to GAIA we used mainly one part Interlux paints.

GAIA although mostly steel has Sitka spruce bulwarks and we religiously painted them with white two part epoxy paints and over coated with white two part polyurethane. They look nice when freshly painted but they do not stand up well with the paint often cracking after a couple or three years. Resanding and repainting, for which we remove them, is laborious.

I suspect that the Sitka spruce is somewhat dimensionality unstable and the two part paints cannot handle the change but I would love to have a more informed opinion.
.
Might it be possible that a one part polyurethane would be more appropriate for this application? On the wooden sloop we never had these problems but we did not sail her in the tropics. We are now in the Rio Dulce and daytime temperatures are 33 and up to 40 deg Centigrade, close to 100 F, in the shade. Normal night time temperatures are around 25 C. On the other hand the temperature range in Canada, where we mainly sailed the wooden sloop, was larger from occasionally -40 in the winter to +40 on a rare occasion in the summer. Daily variation was also higher in Canada but daily highs were of course not as consistently high as they are here.

Does anyone know if the one part paints are more tolerant i.e more flexible and would handle these conditions better?

Jim SV GAIA
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Old 10-07-2020, 14:24   #2
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Re: Two or one part paint?

Your choice

Two part is very hard , high gloss and UV. resistant ....and expensive

Single component , oil based has been used for ever on yachts , its softer, less glossy and half the price

A wooden hull seldom looks good with high gloss

An amateur paint job seldom looks good high gloss
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Old 10-07-2020, 17:15   #3
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Re: Two or one part paint?

How long do you want it to last...?
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Old 10-07-2020, 17:27   #4
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Re: Two or one part paint?

I have used both on my old steel boat...no question, the two part is better, smoother and tougher, etc, for the hull...but I used one part on the exposed parts of the steel deck and the wood dorade boxes, etc, and it worked just fine. Never had any problems with it and being one part, is easy to re-open the can when you want to use it later for touchups, etc....and a lot less expensive. How long will it last....hmmm...hard to say, if you re-coat it from time, a light sanding will do the trick, but if you let it go a long time, more effort is required.
But for the hull, no question, go two part.
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Old 10-07-2020, 17:35   #5
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Re: Two or one part paint?

I sold marine paint for a living for many years. When ever someone put two part poly like Awl Grip on wood it would crack at the joints. The two part paints were not elastic enough for the movement of the wood.
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Old 10-07-2020, 18:52   #6
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Re: Two or one part paint?

Quote:
Originally Posted by HopCar View Post
I sold marine paint for a living for many years. When ever someone put two part poly like Awl Grip on wood it would crack at the joints. The two part paints were not elastic enough for the movement of the wood.
This is great knowledge. Thanks
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Old 11-07-2020, 08:42   #7
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Re: Two or one part paint?

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I sold marine paint for a living for many years. When ever someone put two part poly like Awl Grip on wood it would crack at the joints. The two part paints were not elastic enough for the movement of the wood.
That is more the answer I am looking for. I am happy with the two part paints everywhere except on those long Sitka spruce bulwark boards but if I use alkyd enamel I fear having to regularly, yearly, repaint. What I am wondering about is one part polyurethane and if it is more flexible than two part.

And to answer another comment I would like it to last three to five years and even then not have major repairs but on a soft wood like sitka spruce that may be too much to ask.

My choices are two part polyurethane, one part polyurethane or alkyd enamel. And the real gotcha it will be applied over the old two part system except where it will need sanding to bare wood mainly along the top edges. Unlike a wooden hull I do not have any joints to worry about as I was able to buy sitka in long lengths knot free.

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Old 11-07-2020, 08:50   #8
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Re: Two or one part paint?

sealing the wood first ???...maybe a coat or two of varnish, polyurethane, etc, and then the paint ???
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Old 11-07-2020, 08:52   #9
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Re: Two or one part paint?

I think you are right, you need some flex. Two part paints are quite brittle. A good one part poly ought to do it for that. Alkyd too. Personally I like quality non marine brands better than one part Brightsides.
I love spruce but boy it's soft. I made a bowsprit out of a CVG spruce "propeller blank" once. (6" x 8" x 8 ft) The anchor chain tore it up regularly.
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Old 11-07-2020, 09:04   #10
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Re: Two or one part paint?

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Originally Posted by slug View Post
Your choice

Two part is very hard , high gloss and UV. resistant ....and expensive

Single component , oil based has been used for ever on yachts , its softer, less glossy and half the price

A wooden hull seldom looks good with high gloss

An amateur paint job seldom looks good high gloss
After 60 years of working on boats I do not consider myself incapable of doing high quality maintenance. Many 'amateurs' are perfectly capable of doing good looking high gloss paint jobs . Although remembering all that one learns over that time is not always easy 😊.

I also would differ with you on a wooden hull not looking good in high gloss and do not see why that would be so but that is beside the point. Many wooden boat owners on this forum would vehemently disagree as I would have if I still owned our beloved Nova Scotia built sloop.

However all this does not answer the question which was would single part paints outlast two part if applied over a soft wood like Sitka spruce if the wood is used as the bulwarks? I realise the advantages of two part but I am after the disadvantages other than cost which is not an issue in this application.

Jim SV GAIA
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Old 11-07-2020, 09:47   #11
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Re: Two or one part paint?

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Originally Posted by Cheechako View Post
I think you are right, you need some flex. Two part paints are quite brittle. A good one part poly ought to do it for that. Alkyd too. Personally I like quality non marine brands better than one part Brightsides.
I love spruce but boy it's soft. I made a bowsprit out of a CVG spruce "propeller blank" once. (6" x 8" x 8 ft) The anchor chain tore it up regularly.
Ahh thanks for that. Any idea of frequency for maintenance? We have always removed the boards for repainting but it is not that easy to do from a dinghy.

Years ago on that wooden sloop I mentioned we had a varnished mast made out of Sitka Spruce and like your bowsprit it used to get dinged easily leaving black marks because of water ingress. That meant a lot of work every year. Then one year we had a bright idea. We stripped the mast to bare wood and coated it with a thin epoxy from West System. It soaked in really well. I do not remember how many coats as this is at least 40 yrs ago but we overcoated it with tung oil varnish and it looked fantastic. Yearly maintenance after that was a snap as the blocks and other contacts no longer allowed water into the wood. We had no issues with cracking but tung oil varnish is no doubt much more elastic that two part polyurethane either as paint or varnish.

Were I to do that for a boat used year around in the tropics (I would not) I would consider using a two part polyurethane varnish that had UV protection over the thin epoxy sealing coats. But I would worry about cracking knowing what I know now. We have been using Interlux Perfection Plus down below with good results. This approach has worked well for us down below out of the sun but it is used only over hard woods like Cherry, Mahogany,
Walnut and Ash The varnished deck beams inside are still bright and glossy after 25 years of sailing year around. But life is too short in our opinion to do that outside.

Bad enough to have to repaint our bulwarks too often hence this post. Most Gazelles are built with steel extensions to the hull as bulwarks but we chose to save weight and to avoid welding distortions by making them out of Sitka which we could buy in long knot free lengths. We are mostly happy with that except when we need to repaint 😊

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Old 11-07-2020, 09:53   #12
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Re: Two or one part paint?

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Originally Posted by MicHughV View Post
sealing the wood first ???...maybe a coat or two of varnish, polyurethane, etc, and then the paint ???
We sealed the wood with thinned epoxy but perhaps your suggestion of polyurethane might work out better. Will have to consider that but if we use two part paint again it will have to be a two part sealer.

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Old 11-07-2020, 10:50   #13
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Re: Two or one part paint?

yah, I owned a steel boat for around 15 years....never had a problem with the hull paint...I had the usual zinc barrier coat then several layers of undercoat, then originally a two part finish coat....a Devoe brand two part epoxy coat, but this started to " chalk" after a year or two, so I sanded that and applied the two part polyurethane right over that Devoe paint and never had a problem after that. The deck also " chalked" and here I used the one part...it was just easier, as the deck had so many nooks and crannies, etc...but I also had wood...the companionway drop boards and hatch, dorade boxes, hatch frames, handrails, etc. These were originally varnished, but it was a chore to keep up, so I painted everything...right over the varnish, after a quick sand...the one part polyurethane, I can't remember the brand...Interlux ??...Pettit ?? but after I painted, had years of service without any issues.
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Old 11-07-2020, 10:51   #14
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Re: Two or one part paint?

btw...is that a Ron Barnes built Gazelle ??
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Old 11-07-2020, 11:08   #15
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Re: Two or one part paint?

Quote:
Originally Posted by MicHughV View Post
yah, I owned a steel boat for around 15 years....never had a problem with the hull paint...I had the usual zinc barrier coat then several layers of undercoat, then originally a two part finish coat....a Devoe brand two part epoxy coat, but this started to " chalk" after a year or two, so I sanded that and applied the two part polyurethane right over that Devoe paint and never had a problem after that. The deck also " chalked" and here I used the one part...it was just easier, as the deck had so many nooks and crannies, etc...but I also had wood...the companionway drop boards and hatch, dorade boxes, hatch frames, handrails, etc. These were originally varnished, but it was a chore to keep up, so I painted everything...right over the varnish, after a quick sand...the one part polyurethane, I can't remember the brand...Interlux ??...Pettit ?? but after I painted, had years of service without any issues.
Was the top side wood mainly hard wood? And by years of service do you mean without repainting?

Today I used the Perfection Plus clear polyurethane on some previously oiled cherry trim in the aft cabin after a light sanding and acetone wipe and it soaked into the wood very well. We have done this in the main cabin years ago also over previously tung oiled wood and that after multiple coats turned out well. We are slowly converting all our oiled wood, mainly cherry, to varnish as it stays clean much easier and can be handled repeatedly.. Also water from accidentally left open portlights will not stain it like it does with oiled trim.

But all this is hardwood inside, not soft wood bulwarks outside😊

Thanks again and TX to everyone for the replies.

Jim SV GAIA
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