Patchy Wood

[morris6345]

Seeking advice on an internal wood revarnish. I have lightly rubbed down one of our panels in our boat as it was showing signs of sun damage and some areas were stained. I treated the dark areas with wood bleech which removed the staining. It all looked an even finish before varnishing. It's had two coats of Hempel Dura-Satin varnish and it's gone patchy. The patches seem to be getting worse. It's now been about 4 days since varnished. I've not done anything else as I did not want to make the situation worse. Any advice on getting an even finish. Should I just rub it down and start again?

 

[Tranona]

The bleached areas will be absorbing more varnish hence the patchy colour. It is really difficult to get veneered faces all the same colour. The very least is that you need to remove all the old varnish so you start with bare wood. Wipe it over with white spirit which will show if you still have patches. You may have to resort to wood dye to get an even colour.

 

[Fr J Hackett]

I would echo Tranona in saying it's imperative that you remove all the previous varnish / stain so that you start with a "blank canvas" particularly if you try to bleach sections, it just won't achieve a uniform finish. Preparation is key to any work particularly varnishing and staining of wood.

 

[morris6345]

The bleached areas will be absorbing more varnish hence the patchy colour. It is really difficult to get veneered faces all the same colour. The very least is that you need to remove all the old varnish so you start with bare wood. Wipe it over with white spirit which will show if you still have patches. You may have to resort to wood dye to get an even colour.

Thank you, I will sand it down and perhaps go not so lightly. I'll be careful not to go though veneer. Thank you for your reply.

 

[Concerto]

You do not mention what boat you have and what wood the veneer is. If you have a production boat produced in the last 20 to 50 years, the plywood was most likely finished with lacquer not varnish. Varnish requires 24 hours between coats and attracts dust during the drying period as it is sticky. Lacquer in a 2 part catalyst finish that dries in about 30 to 40 minutes and is does not attract dust, and up to 4 coats can be applied in a day. So boat builders use lacquer for this reason.

To try and solve the mess you now have, you must remove all the old finishes and return to bare wood. Use a scraper rather than sandpaper. I use a 1" chisel that has been ground on a small electric diamond sharpening wheel but leave the back burr as this makes a brilliant scrapper. Regular grinding will be needed to keep the burr sharp. When scrapping watch the colour of the dust. Lacquer or varnish will be in whitish colour but when you touch the veneer it will be a brown tint. Now carefully sand with the grain using a 320 grit paper. If you think it is ready to recoat, check all the old finish has been removed. To do this use a J cloth made damp with water. If the wood is clean, the moisture will be slightly absorbed. Any old finish will stop the moisture getting to the wood.

Personally I would forget using the varnish you have bought for the reasons above. Buy some lacquer. My Westerly Fulmar had Morrells 450 low odour high build up acid catalyst lacquer. It can be mixed prior to purchase to be matt through satin or high gloss. Mine was mixed at 30% sheen. It is only available from Morrells trade counters (they have lots all over the country) and has to be ordered for collection/delivery the next day. Some counter staff say it is only available to the trade, so order it by telephone. The minimum quantity is 5 litres with catalyst, and you will need 5 litres of thinners. A couple of years ago this cost just under £60 including VAT. This will do a complete Fulmar's interior woodwork, so a bargain compared to varnish.

Morrells | 450 Low Odour High Build Acid-Catalyst Lacquer

You may find this presentation I gave to the Westerly Owners Association worth looking at. I did not show the electric diamond sharpener (they were available in Aldi last week for under £20).

https://wiki.westerly-owners.co.uk/images/2/25/Interior_Woodwork_Concerto_PowerPoint.pdf

Hope this points you in the right direction to get a nice finish.

 

[morris6345]

You do not mention what boat you have and what wood the veneer is. If you have a production boat produced in the last 20 to 50 years, the plywood was most likely finished with lacquer not varnish. Varnish requires 24 hours between coats and attracts dust during the drying period as it is sticky. Lacquer in a 2 part catalyst finish that dries in about 30 to 40 minutes and is does not attract dust, and up to 4 coats can be applied in a day. So boat builders use lacquer for this reason.

To try and solve the mess you now have, you must remove all the old finishes and return to bare wood. Use a scraper rather than sandpaper. I use a 1" chisel that has been ground on a small electric diamond sharpening wheel but leave the back burr as this makes a brilliant scrapper. Regular grinding will be needed to keep the burr sharp. When scrapping watch the colour of the dust. Lacquer or varnish will be in whitish colour but when you touch the veneer it will be a brown tint. Now carefully sand with the grain using a 320 grit paper. If you think it is ready to recoat, check all the old finish has been removed. To do this use a J cloth made damp with water. If the wood is clean, the moisture will be slightly absorbed. Any old finish will stop the moisture getting to the wood.

Personally I would forget using the varnish you have bought for the reasons above. Buy some lacquer. My Westerly Fulmar had Morrells 450 low odour high build up acid catalyst lacquer. It can be mixed prior to purchase to be matt through satin or high gloss. Mine was mixed at 30% sheen. It is only available from Morrells trade counters (they have lots all over the country) and has to be ordered for collection/delivery the next day. Some counter staff say it is only available to the trade, so order it by telephone. The minimum quantity is 5 litres with catalyst, and you will need 5 litres of thinners. A couple of years ago this cost just under £60 including VAT. This will do a complete Fulmar's interior woodwork, so a bargain compared to varnish.

Morrells | 450 Low Odour High Build Acid-Catalyst Lacquer

You may find this presentation I gave to the Westerly Owners Association worth looking at. I did not show the electric diamond sharpener (they were available in Aldi last week for under £20).

https://wiki.westerly-owners.co.uk/images/2/25/Interior_Woodwork_Concerto_PowerPoint.pdf

Hope this points you in the right direction to get a nice finish.

Hi,

Thank you for taking the time to reply with the very helpful information. I had not even considered using lacquer. I will have a look at them. As to the wood on the boat I'm not 100% sure. The boat is a Cromarty 36 built in 1988 in the UK yard. We think it's a teak veneer having removed some of the old veneer off the cabin hatch. I'm currently waiting for the veneer to arrive. The hatch is another job I'm undertaking at this time. Most of the wood work is in very good condition. It's just the hatch and the area in the image that needs some work.

 

[Tranona]

It will be teak veneer and probably not thin like more modern panels. No need to go the lacquer route as you will be able to get a good finish with the varnish you have. I have just had the same problem with water stains on a sapele veneered bulkhead and experienced the same patchiness. Really could not face taking all the old finish off so painted that panel white as it fitted the rest of the scheme. Felt bad at covering otherwise good veneer but overall looks better than a patchy repair.

Probably not an option for you, but the secret is to get all the old off first and satin finishes are not difficult to apply.