Varnish- sanding between coats?

Keith-i

Keith-i

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I've just started revarnishing the 'dashboard' in our boat. It's teak veneer and due to poor previous applications over the years I've stripped it back and cleaned it down. I'm using Hempel Dura-satin which involves using 3 or 4 coats of gloss first, before a final top coat of satin. Although the instructions specify the number of coats and amount of thinning, nowhere do they comment on sanding between coats. Any thoughts? Interestingly, International Paints recommend sanding between alternate coats.
 
I would sand very lightly with 320 or 240 grit between each coat, vacuum and tack rag before the following.

If the final finish is to be satin there is no no point in using gloss for the previous coats IMO (unless perhaps if you already have both sorts).
 
BabaYaga said:
I would sand very lightly with 320 or 240 grit between each coat, vacuum and tack rag before the following.

If the final finish is to be satin there is no no point in using gloss for the previous coats IMO (unless perhaps if you already have both sorts).
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Disagree: if you do half a dozen (or more) coats with satin you end up with losing much of the look of the grain of the wood - gloss first then one or two only of satin gives a better look. Personally I put on two or three gloss to build thickness first before sanding (wet) between each further coat. Tack rag before the last two or three coats.
 
+1

jwilson said:
Disagree: if you do half a dozen (or more) coats with satin you end up with losing much of the look of the grain of the wood - gloss first then one or two only of satin gives a better look. Personally I put on two or three gloss to build thickness first before sanding (wet) between each further coat. Tack rag before the last two or three coats.
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Plank
 
pcatterall said:
Tack rag? is this a wipe with white spirit on a non linty cloth?
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Its a piece of cloth impregnated with some sticky substance. Dust sticks to it when you wipe it over a surface. It won't get dust out of crevices though so it's best to vacuum first then use a tack rag.

You can buy tack rags at any decent decorators' supplies shop or on-line. I use Liberon but there are others.

They can last a long time and it's best to keep them in an airtight container between uses to stop them drying out.

You can also make your own http://www.thesuperhandyman.com/?page_id=116
 
Thanks gentlemen. I have done the first thinned coat of gloss. I will continue with another couple of coats then switch to satin. I think I'll also give it a light sand between coats - can't see it doing any harm.
 
One more suggestion - a final coat of 50:50 satin and gloss can give a nice finish - it's what I've used to match some factory-sprayed woodwork.
 
"satin" finish in varnish or paint is attained by adding a "matting agent" to what would otherwise be a gloss finish. Obviously paint manufacturers do this in advance of purchase for off the shelf products but industrial supplies are often sold with the matting agent separate for the sprayer to choose the level of gloss vs satin in a % scale. In opaque paints you don't need to worry but in clear finishes the matting agent, which is not entirely clear can obsure the substrate (ie grain).
You should sand between every coat to "key in" the subsequent layer.
 
Longer ago than I care to mention - working in a boatyard which still used oil varnish - I can still hear my foreman painter :

"Put each coat on as if it were the last one and rub each coat down as if it were the first"

Minimum 12 coats from a strip down in those days !!!
 
stephenh said:
Longer ago than I care to mention - working in a boatyard which still used oil varnish - I can still hear my foreman painter :

"Put each coat on as if it were the last one and rub each coat down as if it were the first"

Minimum 12 coats from a strip down in those days !!!
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Absolutely as true now as it ever was Stephenh! Even with modern Polyurethanes it's still true. It's just that lots of people are satisfied with less, but if you want to have the best you gloss and rub down flat with successive coats of gloss until the grain is entirely filled. When it is entirely uniform and flat, use at least another 4 coats of gloss for depth, rubbing down lightly with fine wet or dry, finishing with 2 coats of matt or "ready rubbed" as we used to call it. The resulting job will be superb and well worth the effort.....
 
I started my first phase of wet sanding last night which has taken the sheen off nicely and flattened it out somewhat. The only problem was that some areas don't seem to have cured fully and the varnish was coming off in tiny 'rolls' (a bit like the 'shavings' left after using a pencil rubber on paper). I will have to wait a bit longer and have another go later. Looks like I've already added the need for at least one extra coat!
 
I find those green "scotch like" pads really good for sanding down.

They seem to take off just the right amount of varnish to key the next layer without going all the way back to bare wood. Makes it easy to build up the coats but keep a clean crisp job. As per others, I agree a tack rag is worthwhile - much better than a white spirit wash. The £1 ones from the chandlery are fine and I can make one last 2 -3 coats of the whole boat. But I always use a new one for the last coat. Don't know why, I just do.
 
Doesn`t it seem like a huge con...... You put this stuff on.....and then you have to sand half of it off again ...before you put some more on...so you can sand half of it off again..and so on ....and so on... There must be an easier way... Some polyurethanes don`t require sanding between coats.......Coelan for one.....but are not really suitable for interior work....are very expensive and not all that user friendly.....but do last...it is claimed..up to ten years.....and then can be more or less pulled off as a sheet......before re-applying WITHOUT SANDING.....It must not be beyond the wit and ingenuity of paint manufacturers to produce something really durable....but then....we would not need to make repeat purchases would we? Has anyone else noticed how many paint companies have been quietly gobbled up by Akzo Nobel
 
But the rubbing down between coats is to produce a flat filled in surface, as well as a good key for the next coat. wet scotch pad is ideal to achieve the super yacht finish.

DO NOT wipe down with a turpy rag between coats, that is the quickest way to make it peel!


PS wash old scotch pads & res use next year., they have years of life.
 
Yes I have noticed with some amazement. 15 years ago when my cabinetmaking business used their products they were relatively unheard of in this country and supplied mainly industrial finishes. There were specialist ranges for different uses and all of high quality but certainly not cheap. Goes to prove that retail success is not always just a matter of marketing men making false promises!
 
NOHOH said:
Doesn`t it seem like a huge con...... You put this stuff on.....and then you have to sand half of it off again ...before you put some more on...so you can sand half of it off again..and so on ....and so on... There must be an easier way... Some polyurethanes don`t require sanding between coats.......Coelan for one.....but are not really suitable for interior work....are very expensive and not all that user friendly.....but do last...it is claimed..up to ten years.....and then can be more or less pulled off as a sheet......before re-applying WITHOUT SANDING.....It must not be beyond the wit and ingenuity of paint manufacturers to produce something really durable....but then....we would not need to make repeat purchases would we? Has anyone else noticed how many paint companies have been quietly gobbled up by Akzo Nobel
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People could always try reading the instructions!
If you put the next coat on before the last coat has cured, it will bond, provided the surface is not contaminated. The makers publish the time window in which this should be done.
At some point though, you have to let everything harden, then sand flat, because (most) varnish shrinks as it hardens, so the grain will seem to be filled, but as it hardens the deeper patches will shrink more and the grain will re-appear.

The international one-pot polyurethane is very good for some work, it allows quick recoating without sanding.
The real deal from a dinghy perspective is 2 pack poly such as perfection, very shiny, very hardwearing, very good UV resistance. We use it on carbon fibre masts where it protects them from UV for several years of constant exposure.
Too hard and not elastic enough for a 'proper classic boat', horses for courses?
 
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