DO and Poly Finish

[YorkshireMartin]

I am working on the display side of a piece of walnut for seating. So far it's had the following prep and treatment:

Smoothing plane then light hand sand at 220, coat of danish. Hand and to 320, coat of danish. Hand sand again to 400 then coat of danish. I left a full day between coats and then rubbed back with 0000 wool. Two days later, I then applied a coat of Rustins polyurethane varnish (satin) with a foam brush. Poly was thinned with 10% spirits.

As I sort of expected, not all of the poly has been absorbed and there is a tiny bit of pooling around denser grain which wasn't there at the time of application.

My plan is to allow it to fully dry and then gently rub back again with the 0000 wool, then thin the poly 50/50 and apply as a wipe on for the final finish.

Can anyone see any potential problems with the final stage or the method I've followed so far?

I'm trying to achieve a satin finish with reasonable durability.

I'd appreciate any advice. Cheers guys.

 

[Phil Pascoe]

Why not stick with D.O.? Why change in the middle?

 

[custard]

Can anyone see any potential problems with the final stage or the method I've followed so far?

Bankruptcy?

Seriously Martin, that's multiple steps too many. You need solutions that are easier and much much faster.

 

[YorkshireMartin]

Can anyone see any potential problems with the final stage or the method I've followed so far?

Bankruptcy?

Seriously Martin, that's multiple steps too many. You need solutions that are easier and much much faster.

It's what I had available :lol:

I do have a couple of trial sachets of Polyx, which are waiting on me to pull my finger out and try.

My name is martin and I am a finishing addict

 

[YorkshireMartin]

Why not stick with D.O.? Why change in the middle?

Because it's a seating surface my friend. Having tested the scratch resistance of this particular DO, I decided that it would lose in a fight between the wood surface and a stud on (not "in"... :lol: ) a pair of jeans.

I'm still in the learning phase so I'm testing and retesting everything. The DO did actually provide a reasonable shine once I'd buffed it, but I thought a poly varnish might just top it off nicely as a finishing coat without being too upset that it's over the top of DO.

 

[Sgian Dubh]

It's not normal practice to put a relatively tough and brittle finish over a soft finish. Whilst adhesion shouldn't be a problem because the finishes are compatible, (both being essentially linseed and/or tung oil, white spirits and a resin, plus some other odds and ends) assuming you're talking about an oil based polyurethane varnish, what you propose is a bit like building a substantial house over poor foundations. Better would have been to have gone straight to polyurethane varnish and omit the Danish oil altogether. You've started now, so I'd just go ahead and add another coat or two of the poly and take your chances. If there are problems later you can always strip off chemically and redo. Slainte.

 

[sunnybob]

if you need hard wearing, stick to wipe on polyeurethane. Thats what it was invented for.

Sand to 360 or 400, apply 2 or 3 coats several days apart. if you wanted to, you could sand to 500 between coats.

Dont dilute any more than 20%, its counter productive.

 

[ED65]

I'm trying to achieve a satin finish with reasonable durability.

That's well within Danish oil's wheelhouse. It's practically what Danish oil was invented for: a satin sheen, providing a modicum of protection in an easy-to-apply form.

Incidentally you can skip all that sanding between coats if you want, do all the sanding up front and then just wipe on, then wipe away as much excess as needed for the product type (no need to wipe away any excess with diluted poly if you don't want to).

You can also stop at 220 nearly all of the time, and frequently 180 is as high as you need go.

 

[MIGNAL]

Fat over lean is the usual mantra. Soft over hard, not the other way around. Hard over soft can lead to crazing, the coat underneath expands and contracts whilst the coat on top doesn't want to. Sometimes you can get away with it if the finish underneath is a very thin coat. One method of French polishing is to soak the bare wood in linseed oil and apply shellac over it. In that particular case the linseed doesn't really form a film, it mostly soaks into the grain.

 

[YorkshireMartin]

Makes sense. Unfortunately the varnish is poor and easily scratched. It shows up white when it's damaged too. I think I'm going to mechanically sand it back and try to rescue it with DO. So basically start over.

Thanks for the advice guys.

 

[ED65]

Fat over lean is the usual mantra. Soft over hard, not the other way around.

That's certainly the rule of thumb in painting, I don't know that it really applies to wood finishing (within reasonable limits). Certainly all varnishes are leaner than oil by definition, yet they're now commonly applied after oiling the wood without a problem.

 

[ED65]

Unfortunately the varnish is poor and easily scratched.

Are you sure you let it 'dry' long enough? A decent cure for oil-based varnish can take days at least, a week or longer if it's a bit cool and damp.

Anyway if it is very soft you'll have a terrible time sanding it all away, I'd try a solvent wipe or scraping before gumming up tons of sandpaper.

 

[YorkshireMartin]

Unfortunately the varnish is poor and easily scratched.

Are you sure you let it 'dry' long enough? A decent cure for oil-based varnish can take days at least, a week or longer if it's a bit cool and damp.

Anyway if it is very soft you'll have a terrible time sanding it all away, I'd try a solvent wipe or scraping before gumming up tons of sandpaper.

I gave it two days but, it also scratched again after 5 days in a different location, its the visibility of the damage, rather than the scale, thats the annoying thing. I think you might be right about sanding but I do have some abrasive that might do it, even if it means going hardcore with the 60 grit initially. I could try planing it off, I wonder how that would work out. I cant see this stuff damaging the edge too much as its so soft.

I'm going to ponder it for a bit.

 

[ED65]

Yes a plane will do it. You'll get some gumming up which is a bit of a pain to clean away but it'll get it done.

A good aggressive burr on a scraper will do the job well too and it's a lot easier to clean a scraper

 

[MIGNAL]

Fat over lean is the usual mantra. Soft over hard, not the other way around.

That's certainly the rule of thumb in painting, I don't know that it really applies to wood finishing (within reasonable limits). Certainly all varnishes are leaner than oil by definition, yet they're now commonly applied after oiling the wood without a problem.

It certainly does apply to wood finishing. You can get away with it but not without taking a risk. A lot depends on how thick the underlying layer is, close to the wood (i.e. very thin) and it's probably OK. Not many people build thickness with DO's, it can be done though.

 

[ED65]

"Within reasonable limits."

I just wanted to highlight that the rule/mantra shouldn't be taken at face value. Wasn't suggesting lacquering over spar varnish or something daft like that :mrgreen: