Varnishing disaster

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SimonA

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I have teak panels under my windows, they started to look a bit ropey with the varnish peeling off and some black sections from water damage. I stripped the old varnish with Nitromors (took ages and several applications), then sanded the panels starting with a coarse sandpaper and working down to a fine paper. I then wiped the wood with a cloth soaked in white spirits and left it to dry. The bare wood looked ok. I then applied one coat of varnish and when it dried I had this mess -

woodwork.jpg


What have I done wrong? Why is it so patchy? It's just clear varnish I'm using, I haven't used wood stain so why is the colour so patchy?
 
SimonA said:
I have teak panels under my windows, they started to look a bit ropey with the varnish peeling off and some black sections from water damage. I stripped the old varnish with Nitromors (took ages and several applications), then sanded the panels starting with a coarse sandpaper and working down to a fine paper. I then wiped the wood with a cloth soaked in white spirits and left it to dry. The bare wood looked ok. I then applied one coat of varnish and when it dried I had this mess -

woodwork.jpg


What have I done wrong? Why is it so patchy? It's just clear varnish I'm using, I haven't used wood stain so why is the colour so patchy?
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looks more like Iroko to me .it appears you have left some old varnish there,
you need to sand down to a uniform finish removing all traces of old varnish.
 
thank you, I guess it's time to strip off the varnish and start again.

It is supposed to be teak according to the original brochure for the boat, but could well be Iroko instead.
 
I have been told that when varnishing to start with dilute varish (white spirit) and gradually decrease the dilution factor. But I'm no expert and have ruined several previously beautifully varished dingies!
 
jimi said:
I have been told that when varnishing to start with dilute varish (white spirit) and gradually decrease the dilution factor.
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Yep - the instructions on Epifanes say (from memory) to start with 50:50, then 25:75, then 10:90, before moving on to plain varnish. This is with Epifanes's own thinner, which I think is the same solvent used in the varnish itself. I would avoid using white spirit instead, but some may know better than me.

Pete
 
I find the important thing with nitromors is to keep it moist - apply a thick coat and agitate with brush but do not brush it out as one does with paint. It can take up to 30mins for bubbling and wrinkling to appear, at this point add more nitromors, particularly to the bits that haven't wrinkled. Do not allow nitromors to dry out and go crusty. Remove wrinkled mess with sharp scraper - steel or glass. Aim for a scraped finish that requires minimum sanding (or preferably none). Wiping with white spirit usually indicates if any varnish is remaining - in which case scrape some more. Look forward to seeing pictures of success.
 
If all else fails try using a heat gun and a cabinet scraper, carefully done you may not remove any of the timber except for a light sanding; above all varnish the area when it is at a moderate temperature, warming the varnish, diluted or undiluted, to about the same warmth, this will avoid the small air bubbles that sometimes appear.


ianat182
 
lotusman said:
I find the important thing with nitromors is to keep it moist - apply a thick coat and agitate with brush but do not brush it out as one does with paint. It can take up to 30mins for bubbling and wrinkling to appear, at this point add more nitromors, particularly to the bits that haven't wrinkled. Do not allow nitromors to dry out and go crusty. Remove wrinkled mess with sharp scraper - steel or glass. Aim for a scraped finish that requires minimum sanding (or preferably none). Wiping with white spirit usually indicates if any varnish is remaining - in which case scrape some more. Look forward to seeing pictures of success.
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Whenever I have stripped wood / plywood i get exactly that effect. Annoyingly, the wood can look pretty good when stripped and carefully sanded, perhaps even oxidic acid treated, but reverts to dark stains with a couple of coats of varnish. I would love to know how to overcome this issue
 
SimonA said:
thank you, I guess it's time to strip off the varnish and start again.

It is supposed to be teak according to the original brochure for the boat, but could well be Iroko instead.
Click to expand...

No that's teak all right. The problem is as you said, water damage. Once it goes black it's unlikely that you will get the stain out by just removing the old varnish. It will look OK after a light sanding but the first coat of varnish will bring back the stain. It's possible that you might get under it by sanding but it's also possible, in fact too easy I am afraid, to sand right through the veneer. There are 2 things you can try when its got that bad. I is Oxalic Acid which might "bleach" out the stain. The other is a darker wood stain over the whole panel. You have little to loose, why not experiment on a small patch? Otherwise if it's a large area Robbins do a 1.5mm teak veneer which is a piece of cake to stick down with impact adhesive....... By the way, always before varnishing give the whole job a wash down with white spirit alone. You will see what it will look like after the first coat of varnish without committing to varnish that way.
 
boatmike said:
No that's teak all right. The problem is as you said, water damage. Once it goes black it's unlikely that you will get the stain out by just removing the old varnish. It will look OK after a light sanding but the first coat of varnish will bring back the stain. It's possible that you might get under it by sanding but it's also possible, in fact too easy I am afraid, to sand right through the veneer. There are 2 things you can try when its got that bad. I is Oxalic Acid which might "bleach" out the stain. The other is a darker wood stain over the whole panel. You have little to loose, why not experiment on a small patch? Otherwise if it's a large area Robbins do a 1.5mm teak veneer which is a piece of cake to stick down with impact adhesive....... By the way, always before varnishing give the whole job a wash down with white spirit alone. You will see what it will look like after the first coat of varnish without committing to varnish that way.
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too "flecky" for teak imho, no real grain definition as teak would have, but wtf do i know :)
 
SimonA said:
I have teak panels under my windows, they started to look a bit ropey with the varnish peeling off and some black sections from water damage. I stripped the old varnish with Nitromors (took ages and several applications), then sanded the panels starting with a coarse sandpaper and working down to a fine paper. I then wiped the wood with a cloth soaked in white spirits and left it to dry. The bare wood looked ok. I then applied one coat of varnish and when it dried I had this mess -

woodwork.jpg


What have I done wrong? Why is it so patchy? It's just clear varnish I'm using, I haven't used wood stain so why is the colour so patchy?
Click to expand...

i had this effect when i sanded my back cabin down to new wood. it turned out it was where i hadent sanded the wood down evenly. use a flat wooden block to keep it even.
 
If I use a wood stain won't I still end up with some parts darker? The wood is solid, not a veneer so no danger of sanding through it.

I did think it looked odd for Teak, a friend has the same boat and his wood looked totally different when stripped of varnish. Mine was one of the last built so maybe they used a different wood. Most of the woodwork is veneers, but the sections under the windows are solid wood. I guess I could always add a veneer if I can't get it to look right with varnish.
 
dunmor said:
i had this effect when i sanded my back cabin down to new wood. it turned out it was where i hadent sanded the wood down evenly. use a flat wooden block to keep it even.
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Thank you. I used a sheet sander (electric), do you think I should sand by hand for a better finish?
 
SimonA said:
If I use a wood stain won't I still end up with some parts darker? The wood is solid, not a veneer so no danger of sanding through it.

I did think it looked odd for Teak, a friend has the same boat and his wood looked totally different when stripped of varnish. Mine was one of the last built so maybe they used a different wood. Most of the woodwork is veneers, but the sections under the windows are solid wood. I guess I could always add a veneer if I can't get it to look right with varnish.
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just sand it back to remove all traces of existing varnish ( darker areas)
 
SimonA said:
Thank you. I used a sheet sander (electric), do you think I should sand by hand for a better finish?
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No, do not sand by hand, if you mean rubbing the sand paper with your fingers. It will leave an uneven surface from the finger pressure. Use either a solid block of wood, or a cork block backed with wood, or the firm plastic hand sanding blocks. All will produce a flat surface.

The trim around the saloon hatch recesses on my boat had water staining around the screws and it looks like that. I couldn't sand it out with a reasonable amount of sanding. One piece I used 80 grit and got rid of it, sanded back to 220 grit, washed in white spirit and all these deep scratches became evident. Much sanding later and I got rid of them.

The white spirit as a trial is a good idea to see what it will be like once sanded. I went for for a matt varnish which sort of dulled the staining a bit, not much though. A colleague recommended Oxalic Acid and said it will probably work. I have not tried that yet. Thats for next season.
 
Links For Varnishing

http://www.defender.com/html/varnish.html
http://www.defender.com/html/varnish-repair.html
http://www.cvrda.org/boats/hintstips/varnishing/varnish_menu.htm

Water damage - Any water that has leaked under the varnish is likely to change the color of the wood, which can show up as dark spots in repairs or even in total re-finishes. Bleach can be used to lighten darkened areas, but it must be used with care because it can leave unsightly 'edges' that are impossible to hide.
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The above is from the middle link. I found these sites useful to learn how to varnish. I achieved good results as a beginner in so far as application of varnish is concerned. Just wish I had carried out the above first. Good luck.
 
SimonA said:
If I use a wood stain won't I still end up with some parts darker? The wood is solid, not a veneer so no danger of sanding through it.

I did think it looked odd for Teak, a friend has the same boat and his wood looked totally different when stripped of varnish. Mine was one of the last built so maybe they used a different wood. Most of the woodwork is veneers, but the sections under the windows are solid wood. I guess I could always add a veneer if I can't get it to look right with varnish.
Click to expand...

It doesn't matter what wood it is really Simon especially if its solid. Sanding if you have the thickness will eventually get you to virgin wood. Good luck!

By the way what I didn't say was that all wood darkens when subjected to UV. Light sanding often gives you light patches and dark patches because you are breaking through the UV affected surface. If you have the thickness don't "tickle" it. Use a course grit paper and take the surface off removing up to 1mm material if necessary, then reduce the grit until you remove al scratch marks. I have just done an area on my boat (complete refit on a new to me boat) Started with 60 grit and followed with 80, 100 and finally 120 by machine before one coat of 50/50 varnish. Then when hard 120 again but this time by hand using a wood block to "flat" down, (sand with the grain when finishing) followed by 4 coats of gloss with 10% thinners, then flat down again and give a final 2 coats of ready rubbed (matt) The result is superb but it takes hours of patience!!
 
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