What is the difference between an oil based and water finish?
Once the solvent evaporates, it makes no diffo, right?
[OP]
Contributor
What is the difference between an oil based and water finish?
Once the solvent evaporates, it makes no diffo, right?
David
Confidence: That feeling you get before fully understanding a situation (Anonymous)
Contributor
I saw your questions yesterday but waited to see if someone with a broader base of experience would answer. Looks like you're stuck with me.Originally Posted by David Ragan
Well, yes, it might make a difference; it depends on what you're doing. Yesterday you were talking dyes. Using a dye that's dissolved in water means you have the extra preparation steps of raising the grain and sanding it back. With alcohol or a hydrocarbon-based solvent like mineral spirits (which is what I'm hoping you mean by "oil based" stain), grain raising isn't an issue. Once the carrier has evaporated, the dye is in and on the wood. Or in the case of pigment-based stain, it's on the wood and in the crevices, held there by a little bit of binder.
Next there's the question of whether your next finishing step can redissolve and smear the prior step, especially if the prior step was a coloring step. The answer is dependent on what stuff you're applying and the method you're using to apply it.
That's a short answer that barely scratches the surface of a big topic. Maybe someone else will add to it.
Chuck Taylor
I agree one of our finish gurus will answer this best but, I turn to water borne finishes when I want no yellowing effect. This is rare for me as I generally don't use colorants at all and like the warm glow of a penetrating oil finish. Folks who want stark white maple to stay that way will often use Minwax WB poly. I have not heard of any oil based product that does not darken the material to some extent. This is moot if you are using something like a jacobean or coffee color ;-).
"A hen is only an egg's way of making another egg".
– Samuel Butler
[OP]
Contributor
The below is re: final finish of polyurethane (my current fave.)
So, If i apply a colorant, and then want to layer something on top of it *without* diluting the color, make the second one oil based, if the first was water.
For instance, if I want to use a polyurethane finish to protect the wood, and did not want to mess with the color I finally achieve using dyes, use water based dyes intially.......that way, the 'oil-based' poly won't dilute the dye (cause it was applied with water/alcohol)?
I ask the above cause a lot of time, we tweak the color then apply finish, right? If we were certain about the color, we could just add oil base dye/stain to the poly and do it all in one shot?
So, all oil based finishes develop a yellowish tone after time?
David
Confidence: That feeling you get before fully understanding a situation (Anonymous)
Contributor
That is a pretty safe approach.
Yes, it's very commonplace to color the wood with dye or pigment stain, followed by clear polyurethane, varnish, lacquer, etc. and call it done.
It's also common to add color to the film finish. That's called toning. The big box stores, for example, carry a line of stain-plus-poly finishes, or you can accomplish it yourself with dyes or pigments that are soluble in the kind of film finish you're using, be it poly, lacquer, shellac, etc.
Finishing schedules can get complicated and involve more than one color, at more than one step. Navigate over to the Homestead Finishing Products site, and under Resources--Articles, look at the Stickley Mission Finish Guide document to see some examples of a multi-step, multi-color finishing process.
Just find a process that gives results you like, and practice it until you're comfortable with it. Then try something new. I'm about to complete construction of a project that I have no idea how I'll finish. It's made from pine, which I normally don't use for a project such as this, but the material I used has special significance. It'll take a lot of experimentation before I'll know what to finally put on the piece.
Chuck Taylor
Contributor
FWIW -
When you apply waterborne dye [I use it all the time] there is a risk that the next coat of anything that goes on will "lift" some of the color. I counteract this with two things:
First - I use only Transfast dye powder. Let it sit overnight. This results in almost no "lift". The liquid Transtint is used as a toner only - it has a lot of color lift if used to dye the wood.
Second - I put on a seal coat of dewaxed shellac. My particular method is to apply 2 coats of 3/4# cut with a padding cloth. This isolates the color from the varnish.
Then - the varnish.
And yes - then the oil-based varnish will add an amber tone.
When I started woodworking, I didn't know squat. I have progressed in 30 years - now I do know squat.
Moderator
The different coatings are largely very picky about the types of carriers that will solubilize them. Polyurethane and lacquer are not soluble in water. they must be modified (usually I believe with acrylic resin) to be water-soluble. So what you buy as 'water based polyurethane' will not leave you with the the same exact resin that you get from oil based poly. I cannot think of a resin or coating that is soluble both in water and oil.
For colorants, the thing to remember is that 'dyes' largely do not contain any binder to lock the color pigment in. Stains often do. Therefore, once the carrier evaporates, putting a topcoat on that has the same solvent will cause a dye to move around. It will do the same on a stain if you do not give the binder long enough to dry thoroughly. If you let the stain dry thoroughly, the binder (a varish-type of topcoat itself) will be hard enough to resist gentle exposure to new solvent (say, from the rubbed or brushed application of a topcoat in that same solvent).
Now, if you SPRAY, then you are putting down the finish in an aerosolized form, which causes the solvent to evaporate quite quickly. Further, there is no mechanical interaction with the surface to agitate and lift the stain or dye, so it's possible to spray a compatible-solvent topcoat over an uncoated dye without issue. This is why people say you can 'lock in' dye by spraying shellac over top - even if the dye was alcohol based. If you tried to brush or wipe the shellac on, you could have issues (DAMHIKT).
It is also worthy of note that proper drying between coats is very important. The reason is that even if the surface is dry to the touch, some solvent is still embedded. It needs to evaporate through the surface. If you cover over with too many topcoats too quickly, you trap the solvent permanently and can have a permanently soft surface (in the case of varnish). If the piece is subject to heat later, it can cause the solvent to evaporate through the partially hard surface, causing blisters. This has happened to me with shellac. Shellac does not cure, and ethanol is volatile in the presence of heat, so it's especially subject to this effect. The way to mitigate this is to apply thin coats OR allow long, adequate, recommended drying times.
Also, if one coat has not dried enough, then if you put down a non-compatible solvent product on top (say a waterbased poly over an oil based stain) then the residual solvent in the bottom coat can prevent the top coat from settling on the surface and hence can impede bonding or can cause wrinkling or bubbling or roughness.
People recommend shooting a barrier coat of shellac between incompatible topcoat layers, but this is no substitute for allowing proper drying time - it's just additional insurance.
Last edited by Prashun Patel; 04-30-2015 at 3:14 PM.
Contributor
There is definitely a difference between nitrocellulose lacquer and water borne "lacquer". The water borne is acrylic and it does not have the same properties as nitrocellulose lacquer. For example, if you allow water to sit on water borne "lacquer" the finish will turn white. If you allow it to sit too long, the finish can come off.
Water borne sprays nice and works in many circumstances but it is not a direct replacement for solvent based finish.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Contributor
Might I suggest to the OP to buy a couple of books on finishing and most all your questions will be answered.
I'll only add that OB and WB products are completely different, even if they both have similar resins. Oil, alcohol, and lacquer based resins are completely soluble in their respective solvent (thinner). WB finishes are emulsions - they are not soluble in water but merely dispersed in it by means of some pretty fancy chemistry. So? Well, it's important for two reasons. With solvent based finishes you can add as much thinner as you want, nothing bad will happen, and when the thinner evaporates you will have a film of resin. With WB finishes you cannot thin them beyond a certain point or you risk ruining their film forming properties when the water evaporates. Beyond that, when WB finishes dry they do not immediately form a contiguous film like solvent based products do. They are little islands of resin that slowly flow into each other because of the additional chemicals added to them and eventually form a nearly contiguous film. With sufficient thickness a solvent based finish will have no holes in it, but a WB finish often will which can lead to lower chemical resistance. That's not universally true, however, and my own testing has shown some WB products to have superior chemical resistance to a comparable solvent based product. GF's EnduroVar, for example, had equal or superior chemical resistance compared to oil based polyurethane.
WB finishes are where most (all?) finish manufacturers have been putting their R&D dollars for several years now, driven by government regulations to reduce VOC's. There are some terrific WB products available these days in almost every category you would want.
John
Contributor
lots of knowledge and experience posted here.. thanks guys for your sharing on this complex subject
Posting Permissions
Reply With Quote