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Author Topic: How smooth?  (Read 1764 times)

Lochen

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How smooth?
« on: February 13, 2010, 10:21:50 PM »

In the picture is a cabin top from a Navel Pinnace I am restoring.. Its made of tin and I've veneered it with .5mm by 5mm mahogany planking. Is sanding with 600 grit sufficient preparation before a satin varnish finish?

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derekwarner

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Re: How smooth?
« Reply #1 on: February 14, 2010, 01:33:45 AM »

 Lochen  .....there many grades of mahogony...so if it is a hard variety with fine grain, #600 W&D paper without water shoud be OK as the preliminary sanding

When you say varnish....do you  mean polyurethyene? ....are you intending to spray or brush? .........in OZ we have Cabots Cabothane satin spray [one pack polyurethane]...it lends it self very well to light coats.....then using up to #1200 W&D with water prior to the final coat .....Derek
 
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Derek Warner

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Lochen

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Re: How smooth?
« Reply #2 on: February 14, 2010, 02:37:00 AM »

Hi Derek

Yes polyurethane. The wood is standard model makers mahogany strip planking and I intend to use a brush. Thanks for the information, it does seem quit a good finish with 600

Barry
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FullLeatherJacket

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Re: How smooth?
« Reply #3 on: February 14, 2010, 08:06:13 AM »

Barry
I would suggest a thinned coat first, to allow the polyurethane to soak into the wood and set up hard. Don't use the Quick-Dry acrylic stuff as it's not waterproof and it doesn't thin with oil-based spirits. Thin about 60%/40% varnish/white spirit and allow to dry for at least 48 hours. When you sand it again with 600 it will take on a silky glow (almost poetry, innit?). Then you can apply as many coats as you think necessary, rubbing down with 800/1000/1200 Wet and Dry as you go. I never apply varnish without thinning it first - even when brushing.
Works for me, but try it out on a scrap piece of veneer first if you're at all uncertain.
FLJ
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Lochen

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Re: How smooth?
« Reply #4 on: February 15, 2010, 12:23:52 AM »

Thanks FLJ.

I've applied one coat of ronseal polyurethane satin interior varnish, I didnt thin it (I dont think it will thin as brushes are washed with water and washing up liquid) so I didnt put much on and brushed it well out. It seems to have dried ok, although as suspected, its made the wood whisker (well in the minutest tiniest teeniest way). Barely detectable. Its  quick drying (2 hours between coats) but I'm going to leave it for your 48 hours before sanding it again.

It looks very nice..............I'm a little bit impressed with myself.  :-))
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FullLeatherJacket

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Re: How smooth?
« Reply #5 on: February 15, 2010, 07:42:21 AM »

Barry
It's 99.9% certain that it's the acrylic stuff you are using, so I'd strongly recommend a few top coats of the Exterior grade, oil-based "proper" polyurethane. It should take OK on top of the other stuff.
Don't forget to use a tack-rag to clean off the sanding dust before you re-coat each time.
FLJ
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Colin Bishop

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Re: How smooth?
« Reply #6 on: February 15, 2010, 09:48:03 AM »

I think there is a bit of a misunderstanding goung on here. If you can wash out the brushes with water & washing up liquid then it isn't polyurethane varnish which requires white spirit and takes several hours to dry. I have a can in the workshop. If you have put quick dry acrylic on then putting polyurethane over the top could be risky and I certainly wouldn't try it as it could take the underlying acrylic off.

If you are using polyurethane then bear in mind that the external variety will give a yellowish tint due to the UV filters it contains. It probably won't matter on wood too much but it can be very noticeable if applied over paint. The interior variety is usually the one to go for as it is more transparent.

If you have been using quick dry acrylic and are happy with the finish then i would leave it at that as it's a cabin roof and isn't going to be immersed. You can always add a second thin coat to ensure that it is weather resistant.

Colin
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Lochen

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Re: How smooth?
« Reply #7 on: February 15, 2010, 02:50:16 PM »

Hmmmmmmmmmm. It says polyurethane on the can..........'advanced polyurethane fomula'. I looked it up 'Ronseal Diamond Hard Floor Varnish is a polyurethane acrylate
dispersion, containing no added lead or free isocyanates'.

I dont know what any of this means. Ronseal eh? what it says on the can................ >:-o

It went on nicely and looks very nice..

Barry
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