When is smooth enough smooth enough?

I am in the process of building the Bluenose which I intend to paint. I have planked the hull and am now sanding the hull and applying wood filler. During the planking process I was also sanding and using wood filler as I went along. The hull has become notably smoother I am using 150 grit sandpaper. As I go along, I find finer and finer areas to apply the wood filler.

My question is when do I stop? I intend to use finer sandpaper until I get to 400 grit. How do most of you determine at what point is smooth enough smooth enough? I realize that this is very subjective, but your thoughts and expertise would be very appreciated.

Rob

I like using automotive spray putty in a rattle can. It gets things perfectly smooth.

If you intend to ultimately paint the model when you think that it is smooth enough spray it with a coat of white or light grey paint. This will highlight blemishes, rough spots, etc. This coat is sacrificial. You will wind up sanding most of it off.

Roger

Bryian said:

I like using automotive spray putty in a rattle can. It gets things perfectly smooth.

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Thank you for this wonderful idea. I was not aware that such an item existed. I will certainly be getting it and give it a try!

Rob

How smooth? Perfectly smooth, that's how smooth. If you are sanding with 150 grit, you're not even close to the right zip code.
The number one flaw that turns what could have been a very good model into a piece of crap in most instances is always a bad paint job. Perhaps it's because so many people think they know how to paint. Painting models isn't like painting walls. It's like painting cars. Any imperfection in the surface will be enhanced by the finish coats. People think, "I've got it smooth enough, I guess." and then they slap the paint on, usually way too thick, and the hull immediately looks terrible.

The real question is "How smooth is it now?" The preliminary sanding using abrasive sheets in the 120-150 grit range is for extreme roughing in really, really gross roughness. 120 grit is generally much too coarse for fine work even for the average strip wood plank on frame kit which is terribly unfair in the beginning due to the construction method itself. It's a bunch of flat slats attached to a curved frame. They have to be sanded to shape so that on the outside, the plank faces are curved to the shape of the hull. This should be done using a "sanding board," a springy strip of wood, plastic, or metal that will bend to a fair curve, with abrasive paper glued to it. (Sometimes you can find fingernail "emery boards" at the drugstore that are springy enough to use for this purpose.) 120 grit is like driving a tack with a sledgehammer. I use 220 grit at the coarsest. If my work is so rough that it really needs "major surgery," it's time to get out the edged tools and start scraping and planing. (Another "tragic mistake" many modelers make is sanding parts to shape. Sanding is for smoothing surfaces or taking a tiny bit off an end to make something fit, not for shaping wood. If you want to shape wood, cut it with sharp edged tools.) A frequent mistake many make is to "chase" unfair areas by "spot sanding" with the paper in their hand. This almost always just creates a lot of "dips" and "humps" in the surface because a specific area is being sanded without regard to fairing it into the level of the entire surface.

Once the bare wood is fair, it should be sealed. I, and many others, use clear shellac for this purpose. It goes on very easily and dries very quickly. It is important to do this in order to provide a good foundation and connection between the bare wood and the coatings that follow. Shellac also soaks into wood surfaces and "hardens" them, so when they are sanded further in the finishing process, the sanding is much less likely to raise "fuzz" on the wood surface. (Basswood is famous for this annoying tendency.) Apply the shellac liberally, but do not permit it to dry and then add another coat because this will create a gloss finish which you don't want. You want the coatings to follow to stick to each other.

When the faired wood hull is sealed and the shellac dry (virtually in minutes), open seams and major imperfections can be addressed. There are specific materials for this. The best products are found in automotive paint stores where the local body shops get their materials or in well-stocked yacht chandleries (not the ones that are more interested in selling sunglasses and "yachting togs.") This stuff is called "surfacing putty." It is a creamy material made up of very fine "whiting" (powdered chalk) and acetone. It can be thinned with acetone. The acetone dries very fast and this stuff can be applied out of the can at the consistency of toothpaste to fill larger seams and divots. The acetone-based surfacing putties will harden in can quickly if you leave the top off, even while puttying. It is easily reconstituted by adding a tablespoon or three of acetone to the can at the end of using it and replacing the top tightly and then turning the can upside down and letting it sit overnight. No need to mix it in. The new acetone is simply absorbed by the material in the can. Apply the toothpaste thick material with a small flexible putty knife or better yet, a palette knife from the art store when working on scale models. (Cleaning your tools with acetone is a lot easier if you do so before the putty starts getting hard. a dirty putty knife isn't smooth and so is useless for the purpose for which it was intended.) When the putty is dry, and it will dry hard very quickly, sand it fair and smooth using 320 grit sandpaper on a sanding board. It's very important to sand curved areas with a curved base to your sandpaper. Otherwise, you will sand "lumps" and "bumps" into your surface.

Is my go-to surfacing putty, primarily because I've used it for decades finishing high-end yacht hulls, as has everybody else in that trade. There's other brands as well. They probably cost lest because anything "with a boat on the label" costs twice as much, it seems. The auto painting shops I think have surfacing putty from 3M that comes in a tube like toothpaste and in some sort of spray cans, too. Probably at less cost than Interlux from the chandlery or online. It does go a long way, though, and you can keep a can "healthy" by adding acetone as needed to maintain consistency. (I guess it's like taking care of sourdough starter. )

Needless to say, don't use acetone with a cigarette dangling from your lips. Use in a well-ventilated space. Read and follow the instructions on the can. Don't whine about the "fumes." Work smart and you'll live. Painters have been doing this for every.

The beauty of surfacing putty is that it is made to be sanded very easily. When using it, sanding becomes quite satisfying, rather than a nasty chore. Apply the surfacing putty conservatively. Fill the divots and dents to the level of the surface. There's no need to pile up gobs of it y9ou will only have to sand off later. If there are widespread areas of minor imperfections, you can thin some of the putty and spread it thinly with a brush. When it is dry, using a "sanding board" again, fair the hull overall using 220 grit abrasive if there are major areas which must be faired, then finish using 320 grit over the whole hull.

Dust the hull well and examine it as you work at this stage. Visible surface imperfections should be sanded down until they are invisible. Paint is not for covering surface imperfections that can be seen with the naked eye!

When your hull is smooth to the eye, if you have sanded through the shellacked wood, apply a light coat of shellac over those bare wood areas and sand very lightly.

Now, you must apply a "sanding base coat" to your hull. Sanding basecoat is a paint that is easily sanded (containing a fair bit of chalk) and contains a lot of solids (pigment) which will cover any color unevenness in the surface below the finish coats. Never forget: It is nearly impossible to cover color unevenness with topcoat finish paint. Don't try to do it. Use basecoat. Basecoat is sometimes called primer, although, usually, primer coatings simply "cover" color unevenness and don't contain solids intended for sanding. Basecoat is rather thick and difficult to apply with a brush without thinning it properly. I usually spray basecoat because it is easier. If you get a "curtain" or run or brushstrokes in your brush application, you will have to sand that all down fair again. Spraying avoids a lot of this. You can get basecoat in spray cans, and I'd advise that if you don't have spray gear yourself. Here again, the automotive paint supply store is your friend. (Don't mess with anything from the "hobby" paint companies. It's overpriced and under quality.) You must cover all unevenly colored areas on the hull with basecoat so that there's no visible difference in the color of the hull when covered with basecoat. Finish coats will not cover color differences! (Except maybe if your topsides are black, but it'll take a lot of it.)

With your basecoat on, your hull should appear completely smooth. If you notice a spot you missed, and you probably will, just like the rest of us, you must go back and address this as needed, whether by applying a tiny bit of surfacing putty, of or touch of basecoat, and when dry, sand again. This is very important, however: If you need to apply glazing putty to a spot, or your sand to bare wood, you must repeat the "coating schedule" buy sealing with shellac and then again with a coating of basecoat. If you apply your finish coat over anything other than basecoat, especially glazing putty, it will show up on your finish coat.

A general word about sanding: Many painters who haven't served a proper apprenticeship sand far too much and far too aggressively. If the proper grit is used, the paper should do the work, not the painter. When sanding between coats to build up a "coating system," as it's called these days. Don't sand more than is necessary. It is not uncommon for inexperienced painters who are sanding between coats to sand so much they sand off the coat they just put on, which is no way to build up a painted surface!

Now you finally get to make your hull smooth! Use something in the neighborhood 400 to 600 grit sandpaper and gently sand the entire hull, removing any imperfections (and repairing those you've missed along the way. Blow or vacuum dust off the surface. Then wipe the surface with a "tack cloth." This is a piece of muslin soaked in a partially polymerized oil and folded in such a way that it can be unfolded to expose a section at a time and is wiped over the dusted surface to pick up further dust. No matter how well you wipe the surface, a tack cloth will pick up more than you thought was there. Buy tack cloths at the paint store. They're cheap. Store them in ziplock plastic bags so they don't dry out. They have a long shelf life that way. Follow the instructions on the package for use.

Once you've got your basecoat finished and tacked, run your fingers over it and test the smoothness of the surface with your fingertips, which are far, far, better at testing for smoothness than your eyes. If it's smooth, you can then apply your finish coats. The thinner and fewer the better, because building up paint thickness that is thicker than scale, while practically impossible to avoid in practice, must be minimized. It's one of the real killers of "a compelling impression of reality," which is what scale modeling is all about. It's far bette to apply many thin coats than thick ones that run and "curtain" and ruin the entire job.

Some spray finish coats, which is the best of all possible worlds. I prefer it because it presents less chance of drips and runs and so on, but that's just me. I can brush a finish that most would not be able to tell from a sprayed one, but I grew up in a family with a bunch of professional painters and decorators and picked up a lot of the trade by osmosis. Use whatever you are best at and if you are uncertain, practice with the options on some scrap before you have a go at your hull. Don't forget to tack before you paint and to carefully sand lightly between finish coats.

When you've applied enough finish coats, which is usually a minimum of four or so, but often twice that, check your hull again for smoothness. I don't know anybody who has ever had a perfect finish at that time. Even the best painters have bugs landing on their finishes now and again. (Trade secret: Never try to remove a bug from wet paint. You will make a mess of it. When the paint is dry, you may get lucky and be able to brush the stuck bug off, leaving no visible sign of the bug's passing.)

All is not lost if you have some very minor imperfections, a speck of dust here or there, for instance. There are two products, rottenstone and pumice, rottenstone being the coarser, as I recall, although they are very close in abrasiveness. They are abrasive powders which for our purposes are applied to a damp soft cloth and hand-rubbed on the finish. The more you rub, the more glossy the surface becomes, but it takes a LOT of rubbing to go from flat to glossy, so don't sweat it. Start with the coarser and proceed to the finer. You will be able to remove the very finest of surface imperfections with this abrasive. It's what's used with oil instead of water to create the famously deep "French polish" finish on the very finest artisanal furniture.

Now it sounds a lot more complicated than it really is, but it really is a lot more complicated than rubbing it with 120 grit and painting hobby enamel on it, too. Many will say it's not necessary to spend a lot of time on painting a model but the one thing that all good models have in common is a good paint job.

Thank you Bob for your very complete feedback. I am starting with 150 grit sandpaper and plan on going up to 400. I construct my own sanding sticks using foam board that has a lot of flexibility to it. I cut a piece of foam board to the shape I desire and coat one side with rubber cement. I coat plain side of the sandpaper that I cut out also with rubber cement. You can then put the 2 together. If you want fresh or finer sandpaper the old one peels off easily and you can put a fresh piece on.

I do use sanding sealer before I put any paint or primer on. My first model dory had exactly the problem with raised grain that you mentioned before I used the sanding sealer. I do use tack cloths before painting to make sure the surface is as clean as can be. I will certainly be trying Bryan's suggestion for using automotive spray putty/primer. After everything is a smooth as I can make it, I will be using an airbrush to apply the paint.

Rob

In engineering, the characteristics of a surface are generally assessed according to two criteria: 1) shape errors, i.e. geometric (non-)compliance with the design, assessed by previously accepted dimensional tolerances, 2) the desired (lack of) roughness of the surface, also assessed by previously accepted standards (although these are essentially separate issues, in certain specific circumstances the latter may also affect the former).

For example, a surface can be polished to ‘ideal’, mirror-like smoothness, but its geometry may still be inconsistent with the design. And vice versa.

Therefore, for example, especially if someone wants to achieve a final visual effect in the form of a glossy paint coating, they should take care of both of these characteristics, because defects in both of these categories will have a negative, visible impact on the final result. Or, in other words, the more glossy the final coat of the paint is, the more visually apparent the imperfections in shape will be. Unfortunately.

However, on the other side, this very feature can effectively be used for visual assessment of the correctness of shapes in terms of their fairness, either by covering the surface of a physical object with a shiny coating (even if the surface is ultimately to be matt) or in design computer applications, as shown below:




The above is just to be on the safe side, since some may not be aware of this phenomenon.

Rob444 said:

Thank you Bob for your very complete feedback. I am starting with 150 grit sandpaper and plan on going up to 400. I construct my own sanding sticks using foam board that has a lot of flexibility to it. I cut a piece of foam board to the shape I desire and coat one side with rubber cement. I coat plain side of the sandpaper that I cut out also with rubber cement. You can then put the 2 together. If you want fresh or finer sandpaper the old one peels off easily and you can put a fresh piece on.

I do use sanding sealer before I put any paint or primer on. My first model dory had exactly the problem with raised grain that you mentioned before I used the sanding sealer. I do use tack cloths before painting to make sure the surface is as clean as can be. I will certainly be trying Bryan's suggestion for using automotive spray putty/primer. After everything is a smooth as I can make it, I will be using an airbrush to apply the paint.

Rob

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Sounds good. I laid out the whole process because I thought other less experienced readers might want to get a "start to finish" overview. As you can see, poor finishing is a pet peeve of mine. It's a lack of knowledge more than anything else and one that should be easy to rectify.

That’s an excellent guide from Bob. The only thing I’d add is that I’ve recently found that a finishing coat of sprayed Testor’s Dullcote will help to get a consistent sheen. This is particularly useful when you have a model with different colors such as a waterline stripe and white/red/copper lower hull.

In the old days, the ship modelers for the Royal Navy used broken glass edges to smooth the wood. (And probably lots of bandages. )

I won't disagree with any of the great information above. But if a wood surface is to be left natural or stained, rather than painted, as many surfaces of our ship models are, excessive sanding is not necessary, IMHO, and in fact can be detrimental, should staining be required. For the many surfaces, sanding only to 220 gives a sufficiently smooth surface, helps emphasize the grain and easily accepts stains. Surfaces that are extremely smooth, sanded with 400+, do not accept stains well. Just my opinion.

Someone on MSW recently wrote that Testor’s has discontinued Glosscote. If that’s true I wonder if they plan to do the same with Dullcote so I checked on Amazon and bought a four can pack. Should be sufficient for the rest of my modeling days.

Roger

Signet said:

I won't disagree with any of the great information above. But if a wood surface is to be left natural or stained, rather than painted, as many surfaces of our ship models are, excessive sanding is not necessary, IMHO, and in fact can be detrimental, should staining be required. For the many surfaces, sanding only to 220 gives a sufficiently smooth surface, helps emphasize the grain and easily accepts stains. Surfaces that are extremely smooth, sanded with 400+, do not accept stains well. Just my opinion.

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I suppose everybody's mileage differs, but as an experienced professional level wooden yacht topside painter, I might consider 220 grit sufficient for coating with sprayed basecoat, after which I'd sand to 320 at least before thinking of laying on a gloss finish coat, and that's at 1:1 scale, i.e. "life size." At a scale of 1:48, using coating material properly thinned "to scale," i.e., as close to that as possible, 220 grit is going to be way too coarse for a scale finish. This isn't to say that coatings can't be applied thickly enough over a surface sanded with 220 grit to provide a smooth surface once the coating levels, but that can only be accomplished at the cost of a lot of obliterated detail.

The nautical term for "a wood surface left natural or stained, rather than painted" is "finished bright." Bright model surfaces, or painted surfaces, for that matter, are taken down to fine grits, ultimately 300 or 400 grit, or even finer, in order to develop a sufficiently smooth surface to accept a fine finish. 220 grit is far too coarse to provide the degree of smoothness sufficient to provide a flawless finish with the multiple thin layers of thinned paint or varnish that produce a fine finish.

Arguably, on a model aspiring to meet the most widely recognized standards of high quality, ("A high-quality scale ship model provides a compelling impression of an actual vessel within the constraints of historical accuracy.") emphasized grain ("figuring") in bright finishes, whether stained or not, is to be avoided as it is grossly out of scale. The fact that a smooth wood surface "doesn't accept stains well," is just "the wood telling you something." on a work of fine art (if the modeler cares,) the wood's own natural finish, modestly enhanced with a thin coating of shellac or neutral oil, has far greater integrity that "a pound of pancake makeup on a tart." Coloring of bright wood is best accomplished with wood dyes which penetrate the wood while not leaving any coating buildup on the surface itself.

"Less is more." The coatings applied to a miniature piece that has any amount of detail should be to scale, which, such being in most every instance impossible, means "as thin as possible." Any buildup of paints, varnishes, and other coatings on the surface of a scale model miniature will obscure the fine detail that is essential to the "compelling impression of an actual vessel" the scale ship modeler strives to achieve. Looking at the large percentage of scale ship models posted online, particularly those by beginning kit builders, the single most damaging shortcoming detrimental to their providing a "compelling impression of an actual vessel" is their lack of finish quality.

Rob444 said:

I am in the process of building the Bluenose which I intend to paint. I have planked the hull and am now sanding the hull and applying wood filler. During the planking process I was also sanding and using wood filler as I went along. The hull has become notably smoother I am using 150 grit sandpaper. As I go along, I find finer and finer areas to apply the wood filler.

My question is when do I stop? I intend to use finer sandpaper until I get to 400 grit. How do most of you determine at what point is smooth enough smooth enough? I realize that this is very subjective, but your thoughts and expertise would be very appreciated.

Rob

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My take; if painting the hull of a modern sailing ship/yacht sanding the substrate to a very smooth surface would be detrimental to the final finishing coat. Why? because sanding finer than 220, 120 leaves the substrate too smooth and may result in primer adhesion issues. thererfore a rougher surface creates a better surface for the initial primer to grip onto.. Once the primer is cured as opposed to just being dry the primer can then be sanded to the desired "Baby Bottom" smoothness.
If questioning any indentations, hollows or imperfections on the hull surface a thin sacrificial different colour coat can be applied to highlight the imperfections and and then thoroughly sanded off until all evidence of this film is gone (auto spray technique). As Bryian has already mentioned 'Auto Primer rattle can is ideal. Of work I've done in the past I start with 220 grit which with constant use ends up similar to 400/800 grit. On the question of topcoats, several thin applications are superior to 1 or 2 thick applications.
If finishing a hull in clear coating, Sand initially, then wipe/wet the timber with clean water. This will raise the wood fibres which when dry gives more to sand off. Repeat if necessary. this method will erase previous water marks etc (invible until clear coated or stained) if the hull is to be stained remember "the finer the sanding the lighter the stain colour will appear. The coarser the sanding the darker the stain colour will appear". It's about 'open/closed pores'. Those are methods I use for painting, staining. May be of no help but one never knows. Cheers.

Bob Cleek said:

I suppose everybody's mileage differs, but as an experienced professional level wooden yacht topside painter, I might consider 220 grit sufficient for coating with sprayed basecoat, after which I'd sand to 320 at least before thinking of laying on a gloss finish coat, and that's at 1:1 scale, i.e. "life size." At a scale of 1:48, using coating material properly thinned "to scale," i.e., as close to that as possible, 220 grit is going to be way too coarse for a scale finish.

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We will never achieve a "to scale" finish, nor do we need to. We are using OUR eyes to view the finish, not the "scale" eyes of some 1.5" tall sailor looking at the finish from a distance of less than a centimeter.

Bob Cleek said:

This isn't to say that coatings can't be applied thickly enough over a surface sanded with 220 grit to provide a smooth surface once the coating levels, but that can only be accomplished at the cost of a lot of obliterated detail.

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Again, /I/ am talking about natural and stained wood finishes, NOT painted finishes. Regardless of grit, detail is not obliterated on wood finishes.

Bob Cleek said:

The nautical term for "a wood surface left natural or stained, rather than painted" is "finished bright." Bright model surfaces, or painted surfaces, for that matter, are taken down to fine grits, ultimately 300 or 400 grit, or even finer, in order to develop a sufficiently smooth surface to accept a fine finish. 220 grit is far too coarse to provide the degree of smoothness sufficient to provide a flawless finish with the multiple thin layers of thinned paint or varnish that produce a fine finish.

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Again, a flawless finish is not necessary or desirable, to me. A flawless finish, even with matt finishes, ends up way to glossy and artificial on models, IMHO.

Bob Cleek said:

Arguably, on a model aspiring to meet the most widely recognized standards of high quality, ("A high-quality scale ship model provides a compelling impression of an actual vessel within the constraints of historical accuracy.") emphasized grain ("figuring") in bright finishes, whether stained or not, is to be avoided as it is grossly out of scale.

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100% agree.

Bob Cleek said:

The fact that a smooth wood surface "doesn't accept stains well," is just "the wood telling you something." on a work of fine art (if the modeler cares,) the wood's own natural finish, modestly enhanced with a thin coating of shellac or neutral oil, has far greater integrity that "a pound of pancake makeup on a tart." Coloring of bright wood is best accomplished with wood dyes which penetrate the wood while not leaving any coating buildup on the surface itself.

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Dyes are certainly an excellent way of coloring, although most modelers don't use them. I use often penetrating stains, such as Watco Danish Oil finishes, in Natural, Medium and Dark Walnut. If you take pieces of cherry or pear, which is mostly what I use, and finish them with sandpaper up to 400 or so, it becomes /very/ difficult to get the color I want. And too many coats produces gloss I don't want. For large areas, sure I'll put a better finish on it, but again, it can become too glossy. I'm sure you'll agree that really smooth wood becomes glossy even without any finish, and that's not what I'm looking for. Glossy varnish or paint on a scale model makes the model look like a toy, rather than a scale representation of the original. Anyhow, that's just the way I like my "tarts", pancake makeup or not.

BTW, I have tried dyes on my last model, bought every color in the world, loved the way they went on bare wood. Then had all kinds of problems with assemblies of different colors, where glues and dyes would run into other areas, making a mess. So I'll use dyes on furniture, which I do make, but not on models.

Bob Cleek said:

"Less is more." The coatings applied to a miniature piece that has any amount of detail should be to scale, which, such being in most every instance impossible, means "as thin as possible." Any buildup of paints, varnishes, and other coatings on the surface of a scale model miniature will obscure the fine detail that is essential to the "compelling impression of an actual vessel" the scale ship modeler strives to achieve. Looking at the large percentage of scale ship models posted online, particularly those by beginning kit builders, the single most damaging shortcoming detrimental to their providing a "compelling impression of an actual vessel" is their lack of finish quality.

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I certainly agree buildup of paint has to be avoided. Varnish matters less, as it won't obscure detail IMHO. But I apply a minimum of finish too, just to enough to get the color and sheen I'm after. And again, IMHO, a smooth shiny wood finish on an 18th century warship is incorrect and is much more detrimental to providing a "compelling impression of an actual vessel".

Again, just my opinion and my comments refer only to wood on a model imitating wood on the subject being modeled.