What varnish or final coating material will adhere well to most sorts of substrates -- oil paint, acrylic paint, raw wood, varnished wood, etc., -- and without preliminary sanding? Polyurethane? Others?
To put it another way, suppose you couldnt tell what the substrate is, but wanted to add a "varnish" to alter the glossiness or matte effect?
Posted by Preston McCall (Member # 351) on :
Polyurethane or Spar varnish will not stay on latex very well at all. Even on One Shot Lettering it yellows and peels in a year. Maybe a water based clear?
On raw wood, Urethane seems to be about the best. I varnished the mahagony seats on my 55 year old boat ten years ago and they look new. The decking, I used a catalyzed Ditzler urethane in 1985 and it still looks fresh. No problem with adhesion. I finished all of the new exterior ash woodwork on a '47 Pontiac woodie in '81 with many coats (ten or twelve) of Spar and it is still holding up very well today, as I just saw the car six months ago and it looks great. It is kept mostly inside, as it is only a trailer queen.
Another alternative is to use Deft. It is a lacquer like finish which evaporates to dry. Spraying is really the best way to get it ultra smooth, but it does come in spray cans (gotta use a good mask). Not a great exterior finish, though, I have heard, but for furniture it is quicker and comes out silky flawless.
Clear shallac is also a great interior clear finish. It thins with denatured alcohol. Can be soft brushed on in many coats to then sand back and coat out a few more final times to get a very good looking shine. It is the most flexible finish.
Now over oil painted surfaces, I imagine either a Spar or Urethane will work. I would harden both the oil base color and the clear.
Preliminary sanding? If you want a superior surface with minimum orange peel, lightly sanding between coats really helps. I lay down three coats of Urethane and let set a few days, then wet sand with 180 and then 320. Then start building up additional coats with 400 wet sanding between. For a small project like a table top, I use spray can urethane for the final coats and it ends up like glass. If you really want smooth, final sand with 600 and then 1200 wet and machine polish with rubbing compound and McGuires #7 using a car buffer (2.25" wool pad) that has a slower rpm, after a couple more days at least. The final shine will look like the hood of a classic car done in lacquer.
Now for not knowing what the substrate finish is... maybe try touching it somewhere unnoticeable with a Qtip with lac thinner on it. If it is latex, it will be a bit gummy. If enamel, it will lift and wrinkle. Tough to really know if it is a very old finish.
It all depends on what you are really going for in terms of how long you need it to hold up and if it is going to be outside. Mayer's book 'The Artist Handbook' can be very helpful, but he was an extremely 'by the book' kind of advisor.
Tell me more about what it is and I will be glad to clue you in more specifically, Dennis.
Posted by Dennis Kiernan (Member # 12202) on :
Well, it's something that comes up all the time, it seems. You've got a piece of furniture or some appliance you bought once. The finish cd be anything at all. Right at the moment it's some old picture frames that I'm cannibalizing and cutting down to fit different pictures. Some of them are wood with some kind of stain and finish to them, some are hand-laid gold leaf, some gold paint, some black paint with an unknown finish.
Posted by Mike Simpson (Member # 20303) on :
For indoor stuff, especially those picture frames, I'd probably go with shellac Dennis. In my experience it'll pretty much stick to almost anything. You can get it in either a spray can or you can brush it on. I cut mine with 1/3 denatured alcohol to brush on like Preston said. The Deft is also a good choice. I use it mostly on raw wood. No experiencce with the rest of it.
Posted by Preston McCall (Member # 351) on :
I have had Deft lift an old finish before on a furniture refinish. Definitely worth trying a drop of it on the bottom somewhere to see if it lifts or wrinkles, unless you just want to break out the nasty stripper.
Posted by Tim Barrow (Member # 576) on :
the unpigmented shellac should work as a barrier to keep just about any top coat from reacting with the next one,as long as you get full coverage with no holidays,....
