MinWax water based, oil modified Poly.... huh?

[Will Blick]

great post Howard, thx.... so I did recall this low grit accurately.....
but its nice to have all these details in one place...

so, is there ever a reason to sand raw wood to say 400 grit?

Also, if you hand plane with ultra sharp blades, the raw wood is glass smooth. Like no sandpaper will ever achieve...what grit equivalent would you think this is equal to? and after hand planing on edging, with such a glass smooth surface, before applying finish, I assume the only sensible thing to do is sacrifice your glass surface and scratch it up with 180 grit b4 applying finish, right? That hurts, but I am assuming you will concur...

[Howard Acheson]

>>>> so, is there ever a reason to sand raw wood to say 400 grit?

**** Some who are applying a pure oil (ie: real, pure tung oil, boiled linseed oil) as their only finish will sometimes sand to 400 grit. In other words they are applying a finish that is totally absorbed into the wood therefore there is no need of adhesion as with a film finish. But, I would recommend instead that the oil be applied with 400 grit paper sanding it in and then wipe it dry.

>>>> Also, if you hand plane with ultra sharp blades, the raw wood is glass smooth. Like no sandpaper will ever achieve...what grit equivalent would you think this is equal to? and after hand planing on edging, with such a glass smooth surface, before applying finish, I assume the only sensible thing to do is sacrifice your glass surface and scratch it up with 180 grit b4 applying finish, right? That hurts, but I am assuming you will concur...

**** There is no issue with burnishing when sanding or scraping so there is no impediment to the adhesion of the finish with a planed surface. So you can apply your finish directly onto the planed surface.

Of interest is that a magazine ran a little test a few years ago. They sanded a board to 220 grit in one section, then scraped another section and planed a third section. The appearance of each section at that point was quite obvious and different. The planed surface appeared much "smoother". They then applied one coat of varnish thinned 25%, let it dry and then lightly flat sanded all sections with 320 paper on a cushioned sanding block. They then applied another full strength coat and let it fully dry. Next they had everyone in the shop look at the board and try to identify which areas were sanded, scraped and planed. They even brought in their office staff. None could discern any difference in the three areas after the finish was applied. The conclusion was that whether sanded, scraped or planed, they all looked the same after being finished.

[Scott Holmes]

Steve,

When I must sand beteween coats on a floor, I use 120 grit screen 1/2 sheet sander that's sold for sheetrock sanding and stick it on a broom handle so I can stand while sanding.

Will, sanding raw wood to 400 grit will burnish the wood and can cause finishing problems. I concur on the glass smooth wood after a razor sharp hand plane could cause finishing glitches; 220 is OK and doesn't hurt as much...

[Will Blick]

Scott, if I understand your post.... you suggest a glass smooth surface from a hand plane is problematic. It should be roughed up with 220 grit before applying finish... right?

Howard, you are stating the opposite.... I think....

or maybe there was a typo, or my comprehension is fading... I am very curious about this...

[Howard Acheson]

The result of using a very fine sandpaper grit--particularly if you use a powered sander--is burnishing the surface which can cause aborpsion and adherence problems. Burnishing is caused by the heating up of the wood causing an extraction of moisture that ends up sealing the surface of the wood. It really has nothing to do with the smoothness of the resulting surface. Planing does not heat up the wood it just shears off the wood. Therefore, there is no heat to seal the wood.

I will say however, that there is no advantage to achieving a planed surface. As the tests in the shop I reported about showed, there was no adhesion benefit to sanding wood to more than 220 grit--in fact sanding to 180 grit was just fine also. Additional smoothing beyond 220 grit did not resulit in a smoother finish after the finish was applied. The application of any finish is going to "raise the grain" requiring smoothing and leveling after the first coat no matter that a plane was used or it was sanded.

The bottom line is that sanding after planing is not going to affect adhesion. BTW, the "planing" I am referring to is hand planing. Surfaces run through a machine jointer or machine planer certainly need further surface preparation.

[Jack Clark]

Of interest is that a magazine ran a little test a few years ago. They sanded a board to 220 grit in one section, then scraped another section and planed a third section. The appearance of each section at that point was quite obvious and different. The planed surface appeared much "smoother". They then applied one coat of varnish thinned 25%, let it dry and then lightly flat sanded all sections with 320 paper on a cushioned sanding block. They then applied another full strength coat and let it fully dry. Next they had everyone in the shop look at the board and try to identify which areas were sanded, scraped and planed. They even brought in their office staff. None could discern any difference in the three areas after the finish was applied. The conclusion was that whether sanded, scraped or planed, they all looked the same after being finished.

Howard, do you recall which magazine? I'd like to try and find that article.

Thanks

[Will Blick]

Howard, thx for nice clear response... its burnishing (heat) that is the culprit, I did confuse this with surface smoothness....
Now I can use my hand planes with no guilt...

While you are tuned into this thread... maybe you can comment on these two issues...

1) MinWax does not NOT recommend spraying any of their finishes / stains. With small pieces, where time savings is not an issue, can you explain in what applications spraying is the preferred method of applying a finish?

2) Is there a reference on the web, which identifies the pros / cons of each finish...sort of a "help me select the right finish for this project" ...... I assume someone must have prepared a check list, or something?

thx in advance...

[Howard Acheson]

Minwax caters to the DIY woodworker/finisher. Spray equipment is not the way the majority of their products are used. Of course, no one recommends spraying oil based finishes. Oil based finishes dry very slowly. The over spray is in the form of liquid droplets that do not dry and will land on everything in the area creating a crust that is impossible to clean up. Spraying oil based finishes should only be done if the finisher has a good spray booth or sprays outside.

Another problem is that finisher formulate their products to comply with various VOC requirements. Spraying loads the atmosphere many more VOC's than brushing. So to keep their products in compliance the manufacturer will not recommend spraying or thinning of their products. Spraying finishes also entails health issues that manufacturers do not want to deal with. A final issue is that many amateur sprayers are not practiced or experienced. They do not set up their equipment properly, they do not thin or prepare the finish properly and they do not use good application techniques. The manufacturer has little or no control over the user and any problems get blamed on the product rather than the user. For a mass marketer, it's not worth the problems.

If you are looking for info on finishes and finishing, there is no better source than Flexner's Understanding Finishing and Jewett's Taunton New Complete Guide to Finishing. Amazon will have them. Get both if you are really looking to improve your finishing.

[Jack Clark]

I think I found the article Howard referred to. It was in Fine Woodworking. You can download the pdf here:

http://www.finewoodworking.com/Skill....aspx?id=24966

[Steven Hsieh]

Howard

I have couple of questions about varnish.


General Finish "Arm-R-Seal" and "Salad finish" are both same thing, they both have same ingridents (urethane resin).

How are they different compare to floor finishes like Pratt & Lambert "Varmor", Minwax fast drying, Varethane, Bona Woodline Poly?

Minwax has a 51% content and the P&L has a 48% urethane content.

[Howard Acheson]

I think I found the article Howard referred to. It was in Fine Woodworking. You can download the pdf here:

http://www.finewoodworking.com/Skill....aspx?id=24966

That's impressive Jack. That was 6-7 years ago. I checked my copy of FWW and the complete article is in there. It can only be viewed on the FWW forums by paid members. But one can sign up for a two week trial. Just be sure to go back in and cancel the subscription otherwise you automatically become a fully member--and will be billed.

[Howard Acheson]

>>>> General Finish "Arm-R-Seal" and "Salad finish" are both same thing, they both have same ingridents (urethane resin).

I don't know that to be true but all oil based varnish (poly is a varnish) have the same ingredients. Varnish is made by mixing and heating a resin (could be alkyd, phenolic or urethane or combination) and a drying oil (typically linseed oil, soya oil or sometimes tung oil) until the two become a new compound called "varnish". The varnish is the thinned so it can be brushed or sprayed.

There are a number of variables that the manufacturer plays with to result in a product that meets the performance characteristics the manufacturer wants to sell. Interior varnishes are typically harder so they contain a higher percentage of resin to oil. Conversely, exterior products are softer and more flexible so the resin to oil percentage is lower. Of course, exterior products will also contain some amount of UV protectorant. In addition, there might be flatters to reduce the sheen. Floor finishes may also have some added to reduce the slipperiness. They will also vary the amount of thinner depending on whether they are producing a brushing product or a wiping product.

Every manufacturer has their own formulas which they consider proprietary. Looking at MSDS can sometimes be helpful but manufacturers are only required to list dangerous or hazardous ingredients. So typically on a MSDS for oil based finishes you will only find the thinner(s) listed.

[Steven Hsieh]

From Bob Flexner book, he said that urethane is susceptible to UV damage.
But did not say if its heat resistance indoors. I know that polyurethane is water resistance.

Does this mean when all three resins are combined, it is water and heat resistance?
Like Arm-R-Seal for example.

Or is it just polyurethane and alkyd?

[Howard Acheson]

Yes urethane (poly, polyurethane all the same thing) is easily and quickly damaged by UV from sunlight even if the manufacturer claims it to contain UV inhibitors. Urethanes will quickly turn yellow, become opaque and begin to crack and peel.

Urethanes are slightly more heat resistant than non-poly varnishes but not by much. Depending on the product, maybe 10-20 degrees more tolerant. Basically, any oil based finish begins to soften and fail somewhere between 140 and 180 degrees. Combining resins in the manufacture of the finish will not make much of a difference. In general, urethane resins are cheaper than alkyd and phenolic resins so manufacturers will prefer to use them particularly for consumer grade big box brands.

"I know that polyurethane is water resistance." Are you referring to a polyurethane finish or a polyurethane resin? The type of resin used in the product has little affect on it's water or moisture resistance. Finishes made with urethane resins are not any more water resistant than finishes made with alkyd or phenolic resins. The much bigger determinate of water and moisture resistance is the oil used in manufacture. Tung oil is slightly more water and moisture resistant than linseed or soya oil so you will find the better marine exterior finishes are made with tung oil.

The number one objective for a finish manufacturer when formulating an varnish for use in exterior or marine applications is dealing with the large changing environmental conditions which can play havoc with adhesion. This means they will formulate with a higher percentage of oil to resin to make the resulting finish more flexible and softer. The means an exterior varnish is not as durable or abrasion resistant as an interior rated varnish. Also, the higher percentage of oil means that the finish will not be a water or moisture resistant which seems to not make sense for an exterior finish. But, remember, it's much more important for the finish to remain adhered that it is to have maximum water and moisture resistance. No one part oil based varnish is totally water or moisture resistant anyway.

I'm not sure about your reference to Arm R Seal. That product is just a urethane and linseed oil varnish. It's fairly highly thinned to allow it to be used as a wiping varnish.

So the bottom line is that all finishes are a compromise. Some are formulated for a particular application. I much prefer a non-poly varnish. Poly tends to be somewhat cloudy and plastic looking. It's fine for high use potentially abusive applications like everyday kitchen tables, hall tables that will have keys thrown on them or for floors. For funiture a good non-poly varnish will look nicer.

[Steven Hsieh]

Howard
Thanks for your help.

Thats the problem, most manufacturers dont tell you what Percentage of resin, type, etc... You will need to know.


From Steve Mickley(hardwoodlumberandmore.com)
He said that:

linseed oil-based varnish made with urethane resin (Polyurethane), soya oil-based varnish made with alkyd resin and tung oil-based varnish made with phenolic resin.

Is that correct?

I'm not sure about your reference to Arm R Seal. That product is just a urethane and linseed oil varnish. It's fairly highly thinned to allow it to be used as a wiping varnish.

For that particular product, it is urethane cooked with linseed oil to make it varnish?

Poly tends to be somewhat cloudy and plastic looking. It's fine for high use potentially abusive applications like everyday kitchen tables, hall tables that will have keys thrown on them or for floors. For funiture a good non-poly varnish will look nicer.

Thats why manufacturers don't use it for kitchen cabinets and bathrooms such. Lacquer is used instead ,more easier finish to repair and more resistance to water?


What is the difference between the 1-part varnish and 2-part varnishes?