Replies

1. 
   Piccioni | Feb 08, 2006 11:06pm | #1

   I'm not an expert, and not that it matters but the water based products I'm familiar with a acrylics. They go on milky and then dry completely clear.

   In my experience, they don't to yellow, while all the oil based finishes I've used do. I have found that they tend to dry real thin, so you have to do a lot of coats with intermediate have sanding to build up depth. You can't use steel wool.

   I don't know if they are compatible with shellac. It could be the shellac will yellow, which could affect the overall look. I have used sanding sealer to good effect.

   I think the acrylic finishes are not as durable as (oil based) polyurethane, especially with respect to damp.

   But, like I said, I'm not an expert.

1. 
   woodworker417 | Feb 08, 2006 11:20pm | #2

   thanks for the reply.  i know that just about everything is compatible with shellac, which itself does not yellow if using high quality shellac.  hopefully someone else will be able to provide some insight into the quesiton of water v. oil-based poly on this question.  thanks, tony.

2. 
   SteveSchoene | Feb 09, 2006 12:10am | #3

   I have a lot of bookshelves and don't see them getting all that scratched so I wonder about the need for extraordinary protection from abrasion. Shellac is very color stable and quite unlikely to yellow over time. I use it on bookshelves all the time.  It it should be scratched it can be repaired in an hour.  It's a lot more durable than most people give it credit for.    

   Waterbased poly would go on clear and would be less likely to yellow than oil based poly.  However, Waterbased poly's protectiveness is more on the order of lacquer rather than oil based poly. And, mahogany is going to become substantially darker than it is after being freshly sanded so extraordinary attempts to preserve lightness will be for naught anyway.  Traditional resin varnish is generally a bit more durable than waterbased polyurethane and at least avoids the cloudiness of polyurethane.  You mentioned clear shellac as an undercoat.  If that means the Zinsser shellac labeled Clear you should be aware that this contains wax, and consequently it is not appropriate to be used under any polyurethane varnish, and especially not under waterborne poly.  Only dewaxed shellac can be used under polyurethane. Traditional resin varnish can be applied over any shellac. 

1. 
   woodworker417 | Feb 09, 2006 01:12am | #4

   Steve -- thanks for the information.  i few residual questions, is you would be so kind:

   - when you say "avoid cloudiness of polyurethane", you are referring to cloudiness only during the application stage and not after its dried, correct?  also, is oil-based poly coudy at this stage as well, or just the water based?

   - apart from durability, are there any other advantages of oil-based poly over water-based?  for example, will it provide a "deeper" look to the finish, or does it basically look exactly the same, if applied correctly?

   thanks much, tony

   ps:  i was taking about ultra-pale, dewaxed shellac.  i am nevertheless concerned about durability bc although its a bookcase, it will be used to house objects not only could scratch more than books, but also they will be moved on and off the bookshelf more than books typically would.

1. 
   SteveSchoene | Feb 09, 2006 03:57am | #5

   The cloudiness I was referring to is the subtle lack of clarity that is a property of urethane varnishes, oil based or water based even after they have cured.  This is likely what accounts for the "plastic" look polyurethane (or poly or urethane--all the same)  can have.  Even non-urethane oil based varnish has considerably more scratch resistance than shellac or lacquer, not quite as much as poly, but I believe thay look better than poly.  Waterbourne goes on "milky" but dries clear--thats not what I was referring to. 

   Mostly oil based varnish will have what you call greater depth.  Its in large part because of the ambering that occurs.  Waterborne varnish can be almost water clear and even give a cold bluish cast to the wood.  Amber dye can be added to the waterborne varnish to compensate for this making the look pretty close. 

    

1. 
   woodworker417 | Feb 09, 2006 04:40pm | #6

   thanks, but what about oil-based poly?  does that impart any additional depth relative to water-based poly, or does it basically look identical to the water based poly once its dried?  thanks tony.  btw, is there a book out there that provides an in depth job comparing all of these finishes?  I have jewitt's latest taunton book and while it find it does an excellent job discussing finishing techniques, it is mediocore at best at evaluating the differences between these various products, and when to use which product.  i am sure there is something better out there for this.  thanks, tony.

1. 
   SteveSchoene | Feb 09, 2006 07:40pm | #7

   Poly is just one kind of varnish typically an alkyd resin  with some added polyurethane resin to make the surface softer, and therefore more scratch resistant.  I never use oil based poly after several initial tests so can't really be precise about depth compared to waterborne poly.  But oil based poly won't have as much "depth" compared to oil based alkyd resin varnish because of poly's reduced clarity. 

   The extra durability benefits the marketing ad writers claim for poly are more apparent than real, except for use on floors.  As a point of reference, almost all of the factory made furniture until very recently used ordinary nitrocellulose lacquer as the top coat finish.  And, its much less durable than the worst oil based varnish. 

   The best book I know is Bob Flexner's Understanding Wood Finishing, revised and updated 

2. 
   woodworker417 | Feb 09, 2006 08:14pm | #8

   thank you!

3. 
   Ronaway | Feb 09, 2006 10:38pm | #9

   Like some of the others, I don't understand the need for the urethane on bookshelves. A clear shellac and waterbased lacquer would be much easier to apply. I don't know what application method that your are going to use, but I doubt that you will get a right off the gun or brush finish that you will be satisfied with especially in a gloss sheen. You will find the lacquer much easier to rub out to a gloss sheen.

   Ron