How Many Finish Coats Is Enough?
Finishers discuss quality expectations and how to meet them. July 11, 2009
My intention is to not cause a bickering challenge amongst us seasoned finishers and those who are learning about finishes but Iím sort of confused and want to put my cards on the table. I see so many postings talking about a stain it and a seal it and top coat it finish. Iíve also read of posters who complain that the finish is failing or rubbing off. My question is: are you folks applying enough coatings of your finish to please the customers demand of a quality, long lasting finish?
Now Iím not asking you all to exceed the manufacturers mill thickness which will certainly create problems down the line, but do you really think that a stain it, seal it, sand it, top-coat it approach is a durable enough finish for a piece of furniture let alone a set of kitchen cabinets?
I realize coatings have developed over the years and that mill thickness is now more important than ever and that Conversion Varnishes and 2K Polys are now in the mix and regular Nitrocellulose Lacquers are not what they used to be. Is a stain it, seal it, sand it, top coat it approach really a professionally applied wood finish?
From contributor J:
I do at least three coats always, although I have tried to train myself to think in terms of mil thickness rather than number of coats. Some people spray considerably wetter than others. Personally I learned to spray doing metal finishing in a production setting where hitting a minimum/maximum mil thickness in one coat was necessary for production. You learn to spray right on the edge of too much being just enough. I carried that habit over into wood finishing and had to learn to force myself to back off a bit.
I think some people spray fewer or lighter coats for a variety of reasons. It may be because they do not want to put the extra time and material into the finish. Less experienced finishers seem to spray on the light side for fear of getting runs and end up being light on mil thickness. I have also seen some finishers going light on film thickness from a fear of exceeding mil thickness limitations with catalyzed finishes. So my long winded answer to the original question is in short, no.
From contributor F:
Agree 100% with contributor J. It depends on the top coat you use for how many coats are required. I use a CV and require 3.5 to 5 mil dry per mfg recommendation. That means I need two topcoats to get maximum durability. I am currently switching to waterborne. Mfg suggest spraying lighter coats, which means I will need three coats to get to the 3.5 to 5 mil. People typically get in the habit of seal it then topcoat it for reasons I donít understand. All the major mfg's have product information sheets that recommend wet film and dry film thickness. Read these, follow these. Confirm your results with a wet film gauge and do the math, or simply use a positector to measure your final dry film. I always make a habit of familiarizing myself with a new product by reading the PI sheets, then following with samples until I am comfortable with the product.
From contributor M:
I tend to disagree to some extent. With the solid contents of some of these post catalyzed products, you can build very well on two coats. Now if you are not experienced and are thinning a product excessively and not getting a build on the edges, you may run into problems. If I am spraying nitro three coats for sure, other than that two only.
From contributor F:
I think what the questioner means is one coat sanding sealer, and one coat lacquer or CV. In my opinion this isnít enough. You need one coat sanding sealer, and two coats lacquer or CV. I will typically skip the sanding sealer as the product I use is self-sealing and does sand very well. I will stain, seal with CV, then top with CV. This meets the mfg's requirements, but does not meet AWI requirements as they call for a sealer over top of the stain.
From contributor D:
I've never sent anything out the door with just a single coat of topcoat. How many coats depends on what the product is. Something high wear like an entertainment center or bookshelves, will get 3 - 4 coats. Interior doors or lighter wear vertical surfaces I can usually get by with 2 - 3 coats.
I've been using mostly water based CV from Target lately, as it's ready to spray right out of the can and has good durability. In the past I used several different finishes, but I find it too much of a hassle to learn to thin, spray, and store many different finishes, at least for a part-timer. Now I can get used to using one finish and concentrate more on the cabinetry. Well actually I guess two finishes, as I have to find something for pigmented finishes also soon.
From contributor A:
When more of the big kitchen cabinet companies started putting in those automated flat lines, the stain, seal, sand and topcoat systems really started to take off. The paint companies reformulated the topcoats to maximize the build in two automated applications. Of course, everyone was using solvent and not water. These lines had been engineered with flash off tunnels and ovens to speed up dry and curing. You could stain, seal, sand and topcoat one side of the doors and drawerfronts in less than 30 minutes, flip them over and do the other side in the same amount of time while running the line speed at 20 to 25 fpm. With that type of system, you just can't seal sand again and put another topcoat on so that was what your quality was. Now, that would be alright with maple and oak, but I thought cherry needed another at least half pass in the sealer, but if the line wasn't designed for that, there wasn't anything you could do. So I feel that was one of the contributors to the stain, seal, sand and topcoat system quality.
From contributor Z:
My drawers all get one coat sealer one topcoat. All cabinet doors and drawerfronts get stain one sealer two top coats.
From contributor G:
Using MagnaMax I usually do two fully wet coats. A third if the money coat doesn't work out well. Usually I have things laying down and can put down 5-7 mil wet without any problems. Vertical applications get thinned a bit more to make it lay out better using an HVLP and heat which will get three coats. When I do three full coats I think it looks to plasticy.
From the original questioner:
I was out to the HD store the other day and I was surprised to see just how "thirsty" the finishes looked on most all of the cabinet displays. I like a piece of wood to look like wood and not one that looks as if itís been tossed into a vat of molten plastic, but most of them looked pretty short on finish.
The oak cabinets looked the worse and then came the maple and then cherry. I donít know if the cabinet companies finish the "sample" in store mock ups separate but it would seem to me that the sample mock ups would be in tip top shape, since they are what sells the jobs.
Most of the cabinets at this HD have been set in place a number of years ago but be that as it may. Itís quite easy to spot a poorly finished set of cabinets.
From contributor R:
As a professional finisher I believe you have to do what the job requires and do it well. That could well be an open-pore close to the wood finish, a semi-closed pore, 40 degree sheen finish or all the way to a closed-pore high gloss, buffed finish just like a custom car. It could also be a Watco oil and wax finish or a tung oil or a French polish with shellac.
I worked for a company that did the flat line one coat of sealer, machine sand in a Heeseman sander and then topcoat. It looked pretty darn good for what it was. It isn't how I like to work but it was fast and profitable. I work for a custom furniture manufacturer now and I get go all out and love it. Usually the cabinets in a place like HD suffer from a lack of sanding more than anything else. If you are doing an open pore close to the wood finish, bad sanding will kill you. (I guess bad sanding kills you on every kind of finish and sanding takes the most time so those production minded shops tend to not do a very good job of it.)
There is a finish I have done with SW CV where you thin it 50/50 with high-flash Naptha, wipe it on the wood with a rag, it dries in about five minutes, scuff with 320, wipe on another coat and after it dries apply wax with a piece of 0000 steel wool and buff with a rag. It looks great and is very durable but really has less than one coat if finish. (I use it on tool handles a lot and I'll tell you it is very durable). So to make a long story even longer I like all finishes no matter how much finish is applied as long as they are done well.
From contributor O:
This is a topic that is not so dear to my heart. I learned to finish in the heavy equipment industry. I used only solvent based products. Three years ago I got a crash course in waterborne finishing. It took over a year before I could produce a consistent finish. We started with a WB urethane. We now use an acrylic WB varnish. I have found that restricting yourself to a specific number of coats often leaves you with a variable level of finish. Since every piece of wood is different I find that inspection of each batch is required. Sometimes I can finish a batch with a seal, sand and two topcoats and it produces an acceptable finish. Other times I have to seal, sand, topcoat, and sand again. One of the issues we ran into with the WB stuff is "milking". It took weeks to figure this one out. Thinner is better and never more than two coats between sanding. Finally I would just add, if you really care about what you send out the door, donít be locked into a set process. Ask yourself, would I want that in my house?