So, you’ve just finished that stellar table top and you’d like to give it a ‘smooth as glass’ finish. What’s a woodworker to do? Why, ‘Fill and Finish’ of course.
There are two kinds of ‘fillers’ – putty type fillers used to fill scratches, dents, and holes in wood, and grain (aka pore) fillers that serve to level out the surface of open grained woods. It’s the latter filler that concerns us here.
Woods such as oak, ash, elm, mahogany, chestnut, walnut, wenge, and teak are characterized as having ‘open grain’ because the wood pores are large. In contrast, ‘closed grain’ woods like hard maple, cherry, poplar, beech, and bubinga, have much smaller pores.
You don’t have to fill the pores of any wood before applying a finish – and a lot of woodworkers don’t. It’s a matter of what you want the final surface to look (and feel) like. If you want to achieve a super smooth finish on open grained woods fairly quickly, then your best bet is to fill the pores before you apply your chosen finish. Good candidates for pore filling are large horizontal surfaces – the tops of tables, desks, sideboards, dressers, fancy boxes, and the like.
Sealing is Not Pore Filling
A sealer coat, washcoat, or a sanding sealer won’t necessarily fill wood pores.
The first coat of finish you apply to a wood surface effectively seals the wood, which is why it’s called a ‘sealer coat’. However this coat doesn’t necessarily fill up all the pores – especially on those open-grained woods I mentioned above.
When you apply that first coat of finish (i.e. the sealer coat), the wood fibres will likely swell, giving the surface a fuzzy texture (known as ‘raised grain’). This is especially apparent with water-based finishes. Before you apply subsequent coats of finish you’ll want to sand off these fibres. Once you’ve sanded back the raised grain, it won’t occur again.
To make it easier to sand back this first coat of finish, many woodworkers will thin the finish with it’s appropriate solvent, or use a 1 pound cut of shellac. This thinned version of the finish is called a ‘washcoat’. In production shops, where they often spray on lacquer or varnish, they’ll typically use a commercial product called a ‘sanding sealer’ rather than a washcoat.
Oil or Water
There are two basic types of grain fillers – solvent (or oil) based, and water-based. You’ll want to use an oil-based filler only with an oil-based finish. However, you can use a water-based grain filler under either an oil-base or water-based finish. I use water-based fillers all the time now. They don’t emit toxic fumes, making them safer to use, better for my health, and better for the environment, and they’re easy to apply and compatible with any finish. The only issue is that, as with all water-based products, they dry fairly quickly. The water-based filler I’ve recently been using is Aqua Coat’s Clear Grain Filler.
If you’ll be finishing with a penetrating finish (tung, linseed, wiping varnish, or oil/varnish blends such as Danish oil), it’s best not to use a pore filler, as these as they don’t cure hard enough.
Colour or Not
If you plan to stain the wood surface, you can do so before or after applying the filler. The fillers themselves come in clear, natural, and some colours. You can add a colorant to the clear or natural fillers. Regardless, the filler will likely take the stain differently from the surrounding wood, and sanding after you stain might result in some of the stain being removed. To avoid disappointment, it’s best to do some test staining on scrap wood cut-offs before you commit to your project.
Easy to Apply
The water-based filler that I currently use, Aqua Coat Clear Filler, is very easy to apply. The only caveat is that you have to work in small sections at a time, and reasonably fast. Though the process is quite simple, I’d suggest you begin by sealing and filling a test piece or two – particularly if you’ve never done this before.
I almost always sand with a random orbital sander, up to 180-grit, followed by hand sanding with 220 grit, in the direction of the grain. After wiping the surface clean with a tack cloth I apply a seal coat. Because I use a fair amount of shellac, and usually have a batch laying about, I seal the surface with a 1 pound cut of blond shellac. I let the shellac dry for a couple of hours and then lightly sand the surface with a piece of used 320- or 400-grit sandpaper. Just kiss the surface to remove any bits of raised grain and dust nubs.
You don’t need to mix Aqua Coat Clear Filler before using it. Just scoop a tablespoon or so and drop it on the work surface. The objective is to pack the filler into the pores of the wood. The easiest way I’ve found to do this is with a rubber squeegee. I suppose you could also use an old credit card. Work the filler diagonally to the grain and don’t forget to do the end grain. Aqua Coat spreads easily, and I find that I can do about one square foot of surface in under a minute. I’ve never felt the need to thin the filler with water.
Using a squeegee makes it easier to control the filler, and usually I end up with a very thin, even coat spread over the work area. You can easily see if all the pores are filled by looking at the surface at an angle, against a bright light beamed obliquely to the surface. Once the surface begins to dull I wipe it down with a cloth, across the grain, just enough to remove any bits of paste that haven’t gone into the pores. I’m not overly concerned about getting every single micrometer of space filled, as I always lay on a second coat of filler after the first coat has dried for at least an hour. Before repeating the process I’ll lightly sand the surface with 320- or 400-grit paper. While I like to let the surface cure for a few days before applying the finish, I don’t think it’s absolutely necessary.
To spray a uniform thickness on a wide surface such as a tabletop, hold the spray gun perpendicular to the work (lock your wrist so you don’t rock the gun back and forth) and overlap each spraying stroke by 50 percent.
Begin with the spray pattern half on and half off the front edge of the surface and then overlap each additional stroke by half until the last, which should be half on and half off the surface.
So you are actually applying a double thickness and calling it one “coat,” but it’s the best way to get an even build.
The thinner and clear-up solvent you should use with shellac is denatured alcohol. This is ethanol, the same alcohol that is included in beer, wine and liquors. But it is made poisonous so it can be sold without liquor taxes.
Sometimes you’ll see methanol (methyl alcohol) sold in paint stores. Methanol works fine for thinning shellac, but it is quite toxic if you are around it for a long time breathing the vapors. So it isn’t a good idea to use methanol unless you are working with a good exhaust.
Isopropyl rubbing alcohol is no good for thinning shellac because it contains about 30% water. The water will cause the shellac to turn white, or “blush.” If you have access to 95-to-100 percent pure propanol or isopropyl alcohol, you could use it for thinning without a problem.
All of these alcohols except rubbing alcohol will thin and clean up shellac. The difference among them is evaporation rate. Methanol evaporates the quickest. Denatured alcohol is next. And propanol and isopropyl alcohol are the slowest.
Another concept we drill in finish training is controlling the environment in which spraying occurs. It always amazes me how many finishers tell me that they prefer to spray outside, because it is just easier than creating clean, controlled conditions in the workshop.
While this may seem convenient to you as the technician, it is not at all appreciated by your spray gun, or the product being sprayed.
Aside from the obvious risks of contaminants and unpredictable lay down of product, the primary problem with outdoor spraying is the unpredictability of wind. The slightest random breeze outdoors will wreak havoc on the transfer efficiency of your gun. In other words, you are shooting at your target, and wind is passing through the surface area, moving and diffusing your sprayed fan.
Remember, HVLP spraying is low pressure. The sprayed fan is very fine, which is the benefit of HVLP spraying to begin with. Because of product loss in the air, outdoor spraying often requires 4-5 coats to achieve the level of finish that can easily be laid down in 2-3 coats in the controlled environment of the workshop.
The wasted product is a big deal, because fine finishing products are often pricy. Why spend twice as much on materials? Further, the time that it takes to create additional finishes due to loss of transfer efficiency puts projects behind schedule. Whether you are a hobbyist or a pro finisher, time is just too precious to waste.
So, with spring coming, rather than embracing the nice weather for outdoor spraying, open up the windows in the workshop and give it a good spring clean and organize. Set up a dedicated spray area that you can control, both in terms of cleanliness and air flow (a simple exhaust fan out a window). The best way to exhaust is to be drawing air away from the finish area, not randomly into it or through it.
These two simple adjustments – straining habits and controlled environment – will make a profound difference in your finished results, while saving you time and money. It’s all about quality and efficiency.
Happy spring and happy spraying!
If you have a spray gun, you can use it to create an entirely different look on the wood than you get wiping or brushing the stain and wiping off the excess. Simply spray the stain and leave it; don’t wipe off the excess.
The key here is whether or not you wipe off the excess, not how you apply the stain. You could also spray the stain and wipe off the excess. But you can’t get an even coloring by wiping or brushing the stain and leaving the excess. You can’t help but leave more coloring in some areas than others. Only by spraying can you get an even coloring everywhere.
The trick is to thin the stain a good deal (say three-to-six parts) with the appropriate thinner and build the color slowly with several coats. You can spray the coats on top of each other while still damp, or you can wait until each coat of stain has dried before spraying the next.
If you try spraying just one coat of full-strength stain (rather than multiple coats of thinned stain), you’ll have great difficulty getting an even coloring. In fact, I feel comfortable saying that unless the object is small and flat, you won’t get an even coloring. You have to thin the stain and apply multiple coats.
You can see from the accompanying photographs the difference spraying and leaving makes. I used the same stain on both sides of both panels.
On the oak panel, I wiped off the excess stain on the left side, and I left the thinned, multi-coat sprayed stain unwiped on the right side. Not wiping off the excess stain caused the oak grain to almost disappear.
On the pine panel, I also wiped off the excess stain on the left side, and I left the thinned, multi-coat sprayed stain unwiped on the right side. Spraying and leaving reduces blotching to almost nothing, but it also muddies the contrasting spring- and summer-growth grain.There is no right or wrong way. It depends on the look you want.
Straining is a topic that we talk a lot about in our Prep to Finish paint training program (preptofinish.com). Conventional wisdom and common sense dictate that straining is a great way to remove contaminants from product while it is still in liquid form. This is certainly true, but there are other, more subtle considerations that make straining a good idea.
Specifically, building the habit of straining ALL product every time you load your cup gun is cheap insurance at a deeper level. As the product world transitions more into waterborne platforms, the practice of shaking a can of product is not recommended. Shaking a waterborne tends to bubble it up right in the can, and even after the bubbles appear to have settled out, they often still transfer through the gun and into the finish.
This makes sense, because even in a low pressure system, there is still pressure and force driving the liquid through the needle. You may not be able to see large bubbles in the cup, but there can easily still be tiny ones inside the liquid form product, that will pass through your gun tip, and lay down with the finish as micro bubbles. This creates backwards motion, because usually we will have to sand the dried micro bubbles smooth to remove the nubs, and do another round of spraying.
I recommend a soft stir and then a full strain of all new product. Using a fine mesh cone style strainer, the product actually gets a “combed” effect through the strainer, so that it enters your cup with ideal consistency and viscosity.
Lately, we have rediscovered the convenience of using a filter stand when preparing product for HVLP spraying. If you don’t have a strainer stand, I highly recommend that you pick one up, as it makes it easier and more convenient to ritualize the straining habit. You don’t have to stand there and hold the cup and can. You can be finalizing your tack wipe on the piece to be sprayed, so there is a bonus efficiency gain through this simple implementation. Simple multi-tasking at its best.
In wood finishing the term “pickling” is generally used to mean adding a white coloring to the wood. (“Liming” is sometimes used to mean the same thing.)
There are two broad methods of pickling. One is to wipe on and wipe off a white stain. The other involves sealing the wood with a first coat of finish, thenwiping on and wiping off a stain.
There is a big difference in the appearance you get.
In the sample shown, a white stain was applied directly to the lower half of the panel and wiped off. The same white stain was applied over a sealer coat on the top half of the panel and wiped off. The sealer coat prevented the stain from coloring the wood as thoroughly. The white coloring was left just in the pores when the excess stain was wiped off.
I’ve always said, it’s not the elephants that’ll kill you, it’s the mosquitoes. The little things that quietly sneak up on your finish, that you don’t realize until it’s too late. We all focus heavily on spraying technique as paramount to achieving high level sprayed finishes. While technique is important, product control begins before you even pull the trigger. Here are a couple of tips to help eliminate product based variables.
This is about product handling.
Sometimes, finishers take for granted what the product itself needs in order to be happy in the process. Product happiness directly relates to spray gun happiness, which transfers right to the finish you lay down. If the product and gun are happy, and your technique is good, the finish should be a thing of beauty.
The term “penetrating finish” is one of the most misleading in the vocabulary of finishing because all finishes penetrate. The term is generally used to describe just oil finishes, which dry slowly so they may penetrate a little deeper than faster-drying finishes. But depth of penetration doesn’t have anything to do with protection for the wood, and it’s here that the term becomes misleading because many people think it does, and some manufacturers claim it does. The common descriptive phrase is that the finish “protects the wood from the inside.”
But the quality of a finish that creates better protection for the wood—that is, protection from moisture getting into the wood—is that it dries hard so it can be built thicker on the wood. The thicker the finish, within limits, the better it resists moisture penetration, and oil finishes can’t be built up because they don’t dry hard.
The better terms to use are “film-building” to refer to finishes that dry hard so they can be built up, and “non-film-building” to refer to finishes that don’t cure hard enough to be built up. Using these terms, oil finishes, and also wax finishes, are non-film-building finishes. Varnish, lacquer, shellac and water-based finishes are all film-building finishes.
It seems that one of the topics I get a tremendous amount of emails about is when folks are having issues due to the heat and humidity. A huge number of woodworkers spray their finishes outside and in doing so, are at the mercy of uncontrolled temperatures. Spraying in these conditions can be risky business.
Most finishes simply do not like to be force dried. When spraying in direct
sunlight the surface of the finish will skim over leaving the underlying finish still soft. The finish can then blister; this is most predominant in solvent base finishes. The surface dries and the air that is trapped in the pores of the wood cannot readily escape.
As the air rises it must now break through the dried film and forms a blister. It is a situation where the direct sunlight is the culprit and being able to shade the surface makes a huge difference.
Another issue as a result of the surface drying rapidly is called “blushing”, particularly in hot humid areas. Again, the moisture is trapped within the finish as with blistering. The solution once again is to shade the surface from direct sunlight. If using compressed air, make sure your air is dry and filtered. Turbine systems are the best solution to ensuring clean dryer air.
Lately, the biggest issue is being able to wipe on any non-oil dye or stain in hot/humid weather. Oil-based stains, because they dry so slowly, are usually not an issue. Gel stains, because of their heavier viscosity, dry quite rapidly. Water base stains and dyes can be very problematic. Alcohol/Lacquer dyes and stains can be all but impossible.
Here are a few tips to help when you find your dye/stain drying too rapidly and not allowing you to wipe evenly.
For oil base gel stains, have a cloth damp with mineral spirits ready. Work in as small an area as possible. The objective here is to be able to wipe the stain on and off before it sets. The mineral spirits will help to prevent the stain from drying as fast, but it can also produce a lighter color so often two coats are required. Just be sure to let the first coat dry thoroughly or you run the risk of the second coat softening and pulling off the first coat.
Waterbase dyes and stains can be controlled to some degree the same as the gel stain. Use a dampened applicator which can help, as well as working in as small a section as possible.
In the case of dyes, premixed dyes are not as good as powdered dyes that you mix yourself. Pre-mixed dyes have chemicals that speed the drying process and they are not typically just mixed with water. Powdered dyes that you mix yourself, because it’s simply water, seem to dry slower giving more work time.
We have experimented with utilizing “Floetrol” which is a paint additive used for slowing the drying process in order to improve leveling of water base paints in water base dyes and stains. Floetrol is available at most hardware and box stores where latex paint is sold. We have found it to be very helpful. Our normal mix is approximately 1 ounce to 1 quart of dye or stain. We have used as much as 2 ounces without issue. We have tested this under numerous water base finishes with no issue. But as always, it is a good idea to test any formula on a piece of scrap to ensure total compatibility.
Without question one of the best ways to apply a dye or stain in hot weather is to spray it liberally, again in as small sections as possible, then immediately wipe it back. The spraying allows for a rapid application of the colorant, thus giving more wiping time before it starts to set.
If spraying is not afforded then you want a good stain pad; it will hold more liquid and allow you to cover more area faster. Trying to take a brush or foam brush and apply a colorant in hot weather is all but impossible. The brushes simply do not hold enough material to allow you to evenly wet any sizable area. Just the short time of having to reload the brush is allowing the dye or stain to start to set.
You will also find that using paper towels to wipe off the excess is very
beneficial. They absorb rapidly and allow you to wipe the surface quicker.
To cut to the chase, the bottom line is you have to move quickly before any of the colorants begin to set. It’s not a bad idea to have someone helping you wipe off almost as fast as you wipe on. The general rule of thumb of allowing the dye or stain to set for a few minutes simply put doesn’t work in hot weather.
As stated above, my preferred method is to spray it really wet and start wiping as fast as possible, and in all cases avoid direct sunlight.
Essentials for Every Woodworker, Novice or Master Woodworker
ECO5 ECO-LOGICAL, ECO-NOMICAL TURBINE SYSTEM Efficient 5 stage turbine
Blow Off Tool In Action
Zhan Viscosity Cup