Painting over varnish

[wombat88]

I plan to paint the bottom of my varnished clinker dinghy this winter. Those of you with old leaky clinker dinghies will know why...

I would normally approach this by rubbing down the existing varnish and making sure it is sound before applying undercoat, paint etc.

Someone mentioned removing all varnish back to the wood before painting. I question whether this is necessary? What would you do?

 

[westernman]

If you want this to be long lasting, take it back to bare wood. Using a hot air stripper will be much easier than sanding.
Once stripped, sand well. The more effort spent on sanding at this stage the better the finish.

Also, depending on the paint system, it might be worth an extra coat of undercoat to start off with. May be diluted to get it to soak into the wood better.

Your varnish is probably a mixture of stuff. Some of which won't make a good bond to paint. And varnish is mostly not hard enough such that a good mechanical bond can be made (after rubbing down) to paint.

 

[wombat88]

I feared that would be the reply, all the varnish is 'traditional' so will come off nicely with a heat gun. Last done about ten years ago. I'll strip it back to the waterline, paint below using something 'traditional and forgiving' and give another coat of varnish to the topsides.

Finding and marking a waterline will be fun.

 

[V1701]

Zinsser shellac based paints would stick but I don't know if they do anything that's supposed to be waterproof. I've used them inside over varnish that's just been lightly keyed, they worked well for that...

 

[ChromeDome]

I feared that would be the reply, all the varnish is 'traditional' so will come off nicely with a heat gun. Last done about ten years ago. I'll strip it back to the waterline, paint below using something 'traditional and forgiving' and give another coat of varnish to the topsides.

Finding and marking a waterline will be fun.

If it's been in the water for any length of time the waterline can't be too hard to find.

I've done it a couple of times on different hull shapes, using a laser level when on the hard. One point bow and one stern marked before you start is all you need to connect the points and mark out the line in between afterwards.

 

[benjenbav]

I feared that would be the reply, all the varnish is 'traditional' so will come off nicely with a heat gun. Last done about ten years ago. I'll strip it back to the waterline, paint below using something 'traditional and forgiving' and give another coat of varnish to the topsides.

Finding and marking a waterline will be fun.

I’d be inclined to remove the varnish, too. With regard to the waterline a decent starting point would be to float the dinghy and take plenty of photos. If you then mark the waterline on the pix, then tape the boat and re float it to check. Sticking with the old maxim of measuring twice to cut (or, in this case, paint) once.

 

[tidclacy]

Why get rid of the varnish?

Is she kept in the water or dry sailed?

Paint will not cure the leaking problem if that is your plan.

 

[ShipHappens]

Anyone seen the tiktok hack to remove varnish? Apparently you use oven cleaner and leave it on for 20 mins and the varnish then just scrubs off ?
Not recommending it like but might be worth a look!