Varnish - "dry spots", but only on the chart table - why ?

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aidancoughlan

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Varnish - \"dry spots\", but only on the chart table - why ?

I started sanding & varnishing several weeks ago on the interior of my Westerly Merlin. The steps, galley area, after bulkhead doors, chart table area. All seems to have gone well, except a strange phenomenon on the chart table : each coat we put on it results in some parts of it ending up with "dry spots" - areas where the varnish doesnt seem to stick to. It only seems to happen on the outside (inboard) side of the flat table top (not on other areas around the table). The chart table top is the only large flat area - everything else has been vertical and/or small horizontal surfaces.

Theories:
I know nothing about varnishing other than what I have recently read here and on the web, but my theories are:

(1) There is something strange on the inboard side of the chart table top surface (or in the wood) which makes it difficult to varnish.

(2) It is to do with the way I am applying it - I start cautiously & slowly on the outboard edge, and work inwards - and subconciously start to move quicker as I move across the surface. Maybe this is why it tends to happen on this side.

(3) I am simply not applying enough varnish to the brush, and it is running out of varnish mid-stroke?

(4) The varnish is not thin enough, and is drying out too quickly on the brush ? I have been using unthinned Goldspar, although I tried thinning the last one about 5-10% to see if it helped. I *think* it might have helped a bit, but still some dry spots.

Any ideas ? Is there a common mistake I may be making ?
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

Could there have been something spilt on it in the past - maybe soaked into the wood preventing the varnish from adhering.
I would guess milky drink spilled or mug rings etc?..


I think sand it down again and give the wood a thorough cleaning with white spirit or similar before trying again - maybe do a small test area first?
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

[ QUOTE ]
Could there have been something spilt on it in the past - maybe soaked into the wood preventing the varnish from adhering.
I would guess milky drink spilled or mug rings etc?..


[/ QUOTE ] I don't think there is anything stopping the varnish from adhering as such - once applied, it sticks ok. However if there is something in the wood it is making it difficult to spread the varnish. No visible mug rings etc, or areas that "look" different.


[ QUOTE ]
I think sand it down again and give the wood a thorough cleaning with white spirit or similar before trying again - maybe do a small test area first?

[/ QUOTE ]
I've sanded down between coats OK - in fact more on this area than on other areas. Maybe the fact I've sanded this more than other areas between coats, the next coat needs to be more thinned. I think I'll try a thinner coat tomorrow & see how it goes on.
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

Could it be that it has been contaminated by silicone at some time?
Perhaps on someones fingers or by a silicone spray nearby. It only needs a tiny amount and it's a pain to get rid off.
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

I agree with Dan, wipe it with a silicone remover before sanding, then sand it and wipe again. Sanding a silicone contaminated area only spreads the contamination but will not remove it.
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

Silicone-remover???? TELL ALL!
It must be some of ye Fyrste-worlde Magick, 'cos I've never seen it out here at the arse of Africa!
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

To get this contaminant out of the wood may be easy. It really depends on how porous the timber is and how deep the contaminent has gone.

I would agree that sanding could only spread the problem.

I would try a very inexpensive cabinet scraper.

Either google or see :-
http://www.amazon.co.uk/s/?ie=UTF8&k...sl_3q10qxfdsu_e
or
http://www.rutlands.co.uk/cgi-bin/psProdDet.cgi/DKD34

This is a thin piece of sheet tool steel (about 150mmx10mm) with a filed burr along the edge. Filing the edge correctly is the part you may have to experiment with. When I used to teach DT, kids of 13+ could do it, so have a go.
Hold firmly in fingers with thumbs pressing the centre bottom away from you, so bending slightly whilst pushing along and not across the grain of the timber.
This scrapes off a thin layer of wood and if done over the area will remove the suface layers hopefully without spreading the contaminant.
Do practice on a scrap of similar wood if possible and you may have to go over a much larger area than the actual patch to avoid ending up with a slight depression by working on just the one small area. Remember, always in the direction of the grain.
I would try a test on one of these areas with a little thinned varnish.
If no good, scrape again and try scrubbing with acetone ( dodgy stuff so read the safety info’)
Once dry, wipe with the thinners advised by the type of varnish you are using. Then when still slightly moist, put a thin coat of 50% varnish 50% thinner on the area and see if you are winning.
If all appears ok and you wish to remove small areas that are not looking dead flat, then sanding may now be appropriate.
Best of luck
Scotty
 
Re: Varnish - \"dry spots\", but only on the chart table - why ?

[ QUOTE ]
Could it be that it has been contaminated by silicone at some time?

[/ QUOTE ]

[ QUOTE ]
I agree with Dan, wipe it with a silicone remover before sanding, then sand it and wipe again. Sanding a silicone contaminated area only spreads the contamination but will not remove it.

[/ QUOTE ]

[ QUOTE ]
Silicone-remover.
Available from any paint shop or car spray outfit

[/ QUOTE ]

Fantastic info above, good plausible theory from DanTribe. I do have some silicone lubricant which I have used from time to time, and it is quite possible that I sprayed some on small pieces while working at the chart table (the boat has been practically turned into a workshop at various times since I bought it a few years ago).

I did down to the boat this evening, and the thinned coat I put on yesterday didnt look too bad. One or two relatively small dry spots ok, but much better than before. I think I will try one more thinned coat to see if it covers it well. If it does, I will leave it at that and hope that whatever it was stays silent. If I still have difficulty, I may try Scotty_twister's scraper method, and some of oldsaltoz's silicone remover if I can find it. Or I may just go sailling at this stage !


[ QUOTE ]
From googling on the web: Silicones are next to impossible to remove. My father worked in an aerospace plant; silicones, including people who had used Pert shampoo within 24 hours, were not allowed within 1000 meters of the clean room. This is because essentially any non-autoclavable part that got silicones on it was ruined.

[/ QUOTE ]
great, I hope plan A works..
 
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