Omer

Varnish peeling off in patches.

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I have a  wooden dinghy built some 10 years ago. It has mahogany skin over plywood.

I varnished it every other year with conventional varnish.  Since last year all varnish is flaking and  peeling of in patches like a skin, revealing bare wood.

I do not know what kind of varnish was used originally and what is causing it to peel off.  Could it be that it was a urathane based varnish and applied incorrectly? could it be that the conventional varnish i applied over it was not compatible with the original one?

Since the parts not peeling off yet look good enough, i am not able to peel all of it and start from bare wood. so what can i do to get rid of it? The patches coming off is as thick as paper. so sanding it all would be quite an effort. Any suggestions?

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You can remove the bulk of the varnish with either a heat gun and a scraper or chemical paint remover such as Strypeze.

The heat gun is faster and easier but doesn't get into corners, so I would use both methods.

Follow by sanding til color is uniform and then minimum six (6) coats of varnish.

 

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Yup that old varnish has gotta go.

Plus 1 on the heatgun.

Epithanes exterior varnish is a good long term investment.

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I have no experience with heat gun and i am afraid of scorching  the wood.  Since it is all in patches how do you apply a heat gun to an area where you have bare wood just next to it? Mind you if that was all uniform you would have bare wood next to it as you go along wouldnt you? İs there a safe way of handling a heat gun?

Any info on two types of incompatible varnishes? What is a synthetic or urathane base varnish as opposed to natural resin based ones. I have an unopenned can of İnternational brand which i have mistakenly bought. What is it good for?

After cleaning the mess should i use that? And if i do can i use a conventional varnish on top of that? 

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1 hour ago, Omer said:

I have no experience with heat gun and i am afraid of scorching  the wood.  Since it is all in patches how do you apply a heat gun to an area where you have bare wood just next to it? Mind you if that was all uniform you would have bare wood next to it as you go along wouldnt you? İs there a safe way of handling a heat gun?

Like a lot of things, try it incrementally. Start with a low heat setting, and work up until the varnish or paint blisters sufficiently to scrape it off pretty cleanly. Have the gun in one hand and the scraper in the other. Take your time. You'll figure it out pretty quickly. The varnish should blister way before the wood gets scorched. I used a heat gun for the first time about 3 years ago, to remove old varnish from my exterior teak. It worked like a charm. Get some good scrapers too. Finally, be careful when you put the gun down - the nozzle gets pretty hot - and don't point it at yourself!:D

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55 minutes ago, Bull City said:

Like a lot of things, try it incrementally. Start with a low heat setting, and work up until the varnish or paint blisters sufficiently to scrape it off pretty cleanly. Have the gun in one hand and the scraper in the other. Take your time. You'll figure it out pretty quickly. The varnish should blister way before the wood gets scorched. I used a heat gun for the first time about 3 years ago, to remove old varnish from my exterior teak. It worked like a charm. Get some good scrapers too. Finally, be careful when you put the gun down - the nozzle gets pretty hot - and don't point it at yourself!:D

if you're using a metal scraper, round the corners off the leading edge,  it'll prevent gouging..   you'd think the manufacturers would produce them that way..

yeah be careful with that nozzle , it'll be hot enough to start a fire or give you a really , realy bad burn...   in reality it's a hair dryer on steroids, you can find them in the paint section at the box store...    

 

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Keep the heat gun moving and pay attention.  You'll quickly get the feel of how much heat it takes to soften varnish.  Don't sweat the small remnants.  THey'll come off with the paint remover or sanding steps.

Keep your scraper sharp with a small file.

I've settled on Epifanes gloss varnish.  Add a bit of Penetrol.

 

 

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The way you describe the situation I wonder if it is epoxy under varnish, the epoxy will tend to peal in big thick sheets compared to varnish. If so it will be more more work, but it still all has to go and the methods are the same.

Not all scrapers are equal, shop at a woodworking or marine store. The ones sold at a big box hardware place will make a mess of things. Sharpen and clean the edges often, a file works but I have had better luck with wet/dry sandpaper on a hard surface like a pane of glass or ceramic cutting board.

I have the least expensive heat gun I could find since they tend to be weaker and I am not very patient. It keeps me from scorching the wood.

 

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If there's epoxy under the varnish, you'll see that it sands whiter than varnish.  In any case, the heat gun will make short work of it, but the paint remover will be less effective.

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If you find it is epoxy be aware that inhaling epoxy dust is bad news and sensitivity to epoxy dust can increase with repeated exposure.

Ask me how I know this. Cough splutter sneeze succumbs to intense nausea. 

 

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I doubt it is epoxy. The guy who built it would not spend money on that :-)

On the other hand i thought bare wood would absorb some of it so that when it peels off you would not be staring at bare wood. Or would you?

Many thanks for all the good advice.

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Did it spend more hours in the sun then normal ?
No wood does not really absorb varnish, it fills the roughness.
AS varnish gets older UV light destroys the flexibility, then it comes off in patches.

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Several brands of heat guns make guns where you can adjust the temp of the air - I have this Steinel http://www.steinel.net/Professional-Heat-Guns/HG2310LCD  which is nice as you can lock the temp adjustment so you don't accidentally push the temp regulator button and suddenly have a very different temp than you anticipated.  Highly recommended - It is a great tool for many applications

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