Sanding a hull

[lustyd]

Hi all, I have finally taken the plunge and bought my first boat. I'd like to repaing the hull above the waterline and need some advice.
I should point out that the boat is a 1970 Vivacity 20 which has already been painted previously - I'm not looking for showroom finish but I want to do the best I can.
The reason for painting is colour (currently light blue) and several patches where paint has worn off. I plan to paint dark blue and change the bottom to red.

I assume that I can sand the top and paint straight on. I know that a reasonably "rough" paper should be used here to allow some grip for the new paint but no idea of actual grade.
Once painted I then proceed to sand again and paint second coat. I believe I then sand with ever finer grades to get a more polished look. Again, no idea what grades to use for this.

If anyone can help with the specifics or point out if I'm going about this the wrong way I'll be very grateful.
Thanks
Dave

 

[Tranona]

You can get good advice on repainting a hull from the paint manufacturers. Most of them such as Hempels, International, Epifanes etc publish guides both in paper form or on their websites.

 

[Twister_Ken]

You shouldn't dry sand the antifoul when you get below the waterline. Dust may be toxic. Use wet-and-dry paper wet.

As Tranona says, look at paint manufacturers' www's for advice on painting topsides.

 

[lustyd]

Thanks guys, hadn't thought of that

I wasn't planning to sand the antifoul, just a quick scrape and brush then paint over.
Cheers
Dave

 

[SHUG]

I did a repaint some years ago on a Sadler 25. I based my approach on two magazine articles. The first was from SAIL April 1999 and the other was YMJan2000.
From this the key points are:
Minimum temperature for painting 10C
Start the rub down with 180 grit wet and dry and finish with 600 Edit: this is probably too fine suggest around 300.
Fill in and sand down any blemishes
Remove all traces of dust
Tent the boat if possible but certainly dampen down the ground to minimise dust
Use "Jenny" rollers to apply and "Jenny"brushes to finish.These are cheap, disposable foam brushes which don't leave bubbles or hairs. It is best to do this in company...one to lay-up the other person to finish. see: http://www.flints.co.uk/acatalog/Jenny_Foam_Brushes_and_Rollers.html
Depending on the state of the hull and the particular paint you use, you may have to apply two coats of undercoat and two of topcoat. If one coat of topcoat looks good...STOP because the second coat either has to go on to a glossy surface or you are going to rub back a perfectly good finish. Good luck!!!

 

[flipper]

Try a small test area first to see if you get a reaction. You never know what type of paint has been used previously. If you paint the whole thing and it reacts, you'll have a hell of a job on your hands. Don't ask me how I know that...

 

[xtiffer]

Error... see below

 

[xtiffer]

Unless you are using AwlGrip & looking for a showroom finish then don't bother with wet sanding, Just flat it off with P220 dry.
(I rarely use P600 unless I am starting to polish.)
Spend your money on an Omega laying off brush.
2 coats should be enough.
Cheers,
Chris

 

[bobgoode]

Sand with 240 grit. Fill and fair. Sand again.
Wipe with tak cloths to remove all debris.
Undercoat.
Two people essential. One rolls on the paint and one lays off with vertical strokes.
Use the best brush you can afford...large , long bristles.
Calm day with ambient temp at least 10 degrees C. Don't paint if hot as you won't be able to lay-off.
Leave a week between coats for th finish to harden (Ask me how I know)
30 foot hull...2 hours per side.

 

[oldsaltoz]

First step is to find out what paint is on it now, the manufacturers or your paint supplier can tell you what you need to carry out a few simple tests to ensure your new coating is compatible.

Avoid the use a 'cover all' primer because this will not prevent the old paint from failing.

I start sanding with a 200 grit dry then fill lows and sand again, clean up with a suitable solvent, based on the old paint type from the tests above.

Good foam brushes and rollers are fine but it will need two people. Always start at the top and work down when cleaning or painting and make sure conditions are right.

Good luck.

 

[lustyd]

Update

OK thought I should update this thread now that the deed is done.

Topsides:
I sanded with 240 grit on a sander then washed the hull. Three of us painted, one cutting in then one rollering then one with a brush at the back. This produced a fantastic result and I would recommend this approach. The paint used was Hempel Brilliant Enamel in brittania blue. The only advice I could offer would be wait for warmer weather! it was 8 degrees when this was done and some of the shadier areas are now a little dull. Unfortunately I wanted this done asap so I accepted the risks and got a reasonable result.

Cove line:
I stuck on some coveline tape - this is straight enough but I do wish I had spent more time.

Bottom:
I scraped and then scrubbed this with a deck scrubber and water. Once dry I just rollered on the new antifoul.

Pics hopefully attached to see the transformation and maybe inspire others

 

[macd]

Once painted I then proceed to sand again and paint second coat. I believe I then sand with ever finer grades to get a more polished look. Again, no idea what grades to use for this.

This is more like the technique for, say, gel coat repairs. If you have a sound, smooth base before painting and follow manufacturer's instructions, you shouldn't need to rub down the final finish.

Like all paint processes, the key (and most of the work) is in the preparation of the surface. Be meticulous.

It probably won't be a barrel of laughs but it could be rewarding. Good luck.

 

[lustyd]

Thanks macd I'm guessing you didn't read the whole thread as this is finished and the pics are above

For the record this was a single coat on the topsides and that is the finish produced by the paint so no further sanding or polishing required.
Dave

 

[macd]

Thanks macd I'm guessing you didn't read the whole thread as this is finished and the pics are above

I thought I had but was obviously only running on three. Glad it all worked out. She looks a treat.

 

[Jim@sea]

All of you boat owners dont shoot me down in flames but my suggestion is hand paint it with 2 pack. When I had my car sales business I also sold vans. I prepared the Transits as if I was going to spray them, then I brushed them. Perhaps over 20 years I brush painted over 100 transits. (Hand painting a Morris Minor bonnet it a nightmare) anyway when 2 pack came in we would do colour changes and spray the outside but do the inside, under the bonnet etc with a brush, again 2 pack.
So when I came to paint a boat I did it with 2 pack. Sand it down with a orbital, and get stuck in. The advantage with 2 pack is that even if you get runs once it sets (7 days) you can carefully flat out any marks or runs with 1000's or 1200's wet and dry which leaves you with a matt area, which you then polish up to a shine with brazing paste and a polisher. So if you are careful nobody knows it been painted by hand.