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[peterpan]

Hi
I put my first post on Chit Chat (see New boy with Bruma kit with pics) a couple of weeks ago and got some sound advice on varnishing the hull of my boat.The bottom had been spray painted red and I wanted to varnish the wood topsides which had had several coats of sander sealer each fine sanded back to wood.
 
I have now applied 4 coats of polyurethane gloss varnish each rubbed back with very fine wet and dry and got a fantastic glass like finish.

When I painted the bottom I had got the water line a bit wrong and decided to to paint a white boot top strip and began to mask it off.
I then noticed that where the varnish met the painted bottom the masking tape was pulling the varnish up and to my horror found I could pull ALL of the varnish off in sheets back to the perfectly smooth wood surface I started with . .

HELP

[Circlip]

What is the sanding sealer base solvent?? If it's the standard cellulose base you have a compatibility problem (Which you already know) in that the Polyurethane can't "Bite" into the surface. You need a clear gloss with the same base as the sealer.

  Regards  Ian.

[vintagent]

I used to use epoxy or sanding sealer to seal the grain and then Schooner yacht varnish, though I found that a one pound tin from the boot fair was just as good as the Schooner and didn't skin up like the Schooner.  The key is to get a good, er...key! by rubbing down meticulously and then wiping with preclean or with a rag dampened with gun wash.  Only dampened, mind immediately before varnishing.
And whatever you do, don't use wire wool for rubbing down. It gives you a beautiful finish and a week later it's rusting microscopically!

Regards,
Vintagent

[peterpan]

Thank you both for the excellent advice. My complete lack of knowledge on the varnish/paint front is showing.

Circlip, thank you for identifying the problem which now enables me to seek a solution.

Unfortunately this is not as straight forward as it would be in the UK. Here in Spain there is not a modelling culture (they are big on plastic mystical figures) and there are no model supply's shops. Genuine model mataerials have to be sourced in the UK and the shipping restrictions on all things solvent based means we have to look locally.

The sander sealer I have used was recommended by a fellow model maker here (who has also strongly warned me off anything with polyurethane ??) who found it in a large paint supply shop.It is Italian made called Sirca and at the moment I cant identify what the base solvent is (it says Fondo Nitro FNT04 on the tin ????). I have the same problem with obtaining thinks like preclean or gun wash (sorry don't know what this is). Its the same with acrylic paint which I can only get in very large expensive cans in motor supply shops.

Enough of my moaning (at least its sunny). I am going to test the products I can get in different combinations until l find something that works. I did do a number of different tests on varnishes for colour and finish but not on top of sanders sealer. Your input and advice is a great help in getting me on the right track.

[peterpan]

Sorry guys.....if you see this have just had a thought.

If I find a different sander sealer which I know is compatable with a varnish i have can I apply this over the existing sander sealer or will it react as the varnish did ?

[DickyD]

Sorry guys.....if you see this have just had a thought.

If I find a different sander sealer which I know is compatable with a varnish i have can I apply this over the existing sander sealer or will it react as the varnish did ?

You will have the same problem.

Send a PM to Footski he's in Spain so might be able to help with sourcing materials.

[barryfoote]

PM sent. Over here, the sanding sealer will be cellulose based and as such a cellulose based varnish is required over the top. TKrom do a great line in car paint and varnish in spray tins which should do the job nicely.

[vintagent]

I've never used spray varnish, although I have used cellulose clear one shot over cellulose metallic paint, whixch worked perfectly of course, on my full sized boat's engine.
Cellulose (nitro) sanding sealer doesn't need a cellulose finish.  very little will react with a cellulose sealer.  give it a while to olose all its solvents. Three days is plenty and then go over it with any oil based varnish as I said above, but IF you can get the spray varnish, by all means use that, but try it out on some test piece first to learn how the can behaves.
They are all different.
My own thoughts on acrylic paint aren't printable!  I have been a professional modelmaker for 40 years and I always use cellulose. It has NEVER given me a problem. Fortunately we CAN still get it over her despite the worst that Europe can throw at us. 
Only very recently has acrylic in rattle cans from the car shop been usable, but it still has problems with certain substrates and certain overpaintings.  If you can get cellulos/nitro/laquer, use it!

regards,
Vintagent