Wood Final Finishing
Wood finishing is an art and skill which involves a passion for bringing that unique beauty out from the wood. I personally like natural finished where we put a layer of transparent coats of polishes on the surface of the wood. It gets interesting with the character and beauty of wood grains. Now a day’s multiple options are available to put paint on the wood, but my point is what is a use of wood if you want to hide its beauty. Rather use plastic or other synthetic materials than wood.There are different ways and methods that one may choose to put polish on the finished wood. I personally prefer the finishing with the spray gun which we use to consistent quality and bulk operations. To start with below are the equipment’s required for basic wood spray finishing performance and durability in usage and safety and environmental requirements. Wood being designed in the different way for different products it is important to understand the focus areas in such products ex. – round/curvy edges in case of furniture’s, inner areas in case of musical instruments. Finishing should bring strength to the wooden product by ensuring design and joints should not open up in service and crack the overlying finish –
– Air Compressor
– HVLP Spray Gun
It’s interesting to know the size of compressor – one probably not gone be able to use small compressors which are as small as like a pancake machine as it’s not being able to generate enough volume to finish at least one piece of the finished product. Most of these small compressors are unable to push enough CFM which is the amount of airflow to be able to spray using a good quality spray gun. Hence mid-level compressor is recommended for spray finishing to start with. We have few huge compressors which support our multiple spray booths or spray lines. It is important to understand the air pressure generated by a compressor as we don’t want to drop any pressure when we spray a big piece of the wooden component which requires moving across from one side to another.
For Spray Guns, it is important to choose the one relative to what product we are spraying or using. The variety of guns is available in the market starting from basic to high end. For nice even film finishing using polyethylene or lacquer etc. it is sufficient to have a basic to medium end guns for woodworking.
The usual or basic controls or settings in almost all Spray gun 1) Fan Pattern 2) Flow (Fluid Control Mob) 3) Input Air Pressure These are the main things needs to right any time before we start the spray polishing. The fluidity from spray gun is a tricky and depends on the component or the product that we have as an object to spraying on. We can feed the amount of material to come out of the gun by adjusting the pressure using the trigger. The amount pressure throughput from gun nozzle depends on how far you pull the trigger of a spray gun.
The air pressure gauges help us to measure the exact pressure at which we are spraying from the gun. When you get a new gun, most of them have a suggested pressure that comes with it but that’s really relative to what kind of set up we got. The recommended pressure is for optimum set up in an ideal word. Practically all we need is an enough pressure to get the material out of spray gun and itemize it over the target object. To add on the air pressure for the different material varies as it all depends on the fluidity of the material we are spraying using a specific gun. The material with less fluidity may require the higher pressure than the material with high fluidity.
It is important to have a right Fan Pattern set up in the gun to get a nice consistent or even spray pattern on the object. We can open the fan pattern as much as we want through the Fan Pattern adjustment knob on the spray guns. The Fan Pattern set up also depends on the type of material we are using to spray. The wider spray fan in vaporable NC-based materials may end up in more evaporation during spray than the material on the spray object. The smaller fan pattern may result in pushing more material in a smaller amount of space which is going to make it lot harder to be consistent. Instead, the required result or look can be achieved by opening the fan pattern and have overlap and more. This will help in bringing more efficiency in getting required consistent result through the contentious spray. The throughput by using this technique will be much higher than the traditional way of spray painting. We recommend not to have thick film build on the wooden surface which may be a result of the smaller fan pattern. The bigger Fan Pattern will help us to itemize or break down the surface in the much better way to make it nicer and more even coat. That way it protects from having a thick plastic look that we recommend avoiding.
One of the common technique that we use and recommend is to start and stop spray outside of the area of Spray panel or object areas. If one stops and hesitate for a while inside the spray panel or object we get lot more build up on the two ends of the sprayed panel. Hence it is always a practice to start and stop spray outside the spray panel or object. A build up on the side edges of panel brings an uneven finishing look which impacts the overall look and feel of the final product.
Thinning different products for a good flow out from spray machine is an important aspect in wood finishing. Different products like oil based gloss paints, varnishes required the different level of viscosity to get an ultimate final finish. For smoother flow in finishing, it needs to be thin enough for a fine mist, but thick enough to get the good application on the surface. The viscosity of spraying material can be simply measured using stir stick. Simply lifting out the string stick by dunking into the material we should be able to count the time it takes for the steady stream material coming off the break into dripping. It usually takes 20 to 25 seconds for paint whereas it takes 15 to 20 seconds for oil based varnishes. Most of it also depends on what we are finishing. We need the larger gun tip and more pressure for high viscous material. Adding thinner into the highly viscous material will help to smooth out the spray on final objects.
Staining is a process or rather a technique of enhancing the color of wood during finishing. Various types of staining colors are available in the market to bring enhanced beauty from wood. Water and oil based staining are widely used in markets to stain the wood.
Though wood has a natural breathtaking beauty there are various factors which demand one to use staining in finishing the wood. One of the reason is it doesn’t match the other colors or wood tones in our home. As described in characteristics of wood, wood is the natural product it varies its natural depth of color, grains from tree to tree even if they are from same wood species. Staining should enhance the appearance of wood by reducing color variation between and within sapwood and heartwood. Adding stain to bare or stripped wood can both change the color and highlight the grain pattern of an interior wood.
Stain can be applied manually by wiping it on the surface of wood by using cotton, clothes or specified brushes (Foam Brush) or it can be sprayed on the surface by using spray guns. I personally prefer and recommend staining using spray guns as it has an ability to get into an integral part of wood at low pressure, minimal overspray, production, and an ability to gradually walk a color in the wood. Staining using Spray Guns as prescribed in Spray Finishing will give us an ability to control the darkness or lightness of shade by gradually over spraying over the surface of the wood. We lose this unique flexibility by staining manually using legacy hand staining. Staining the complex wooden structures such as dental moldings, carved products etc. are much more easy, convenient, and symmetric that uniform stain color on these products will be achieved only using Spray Staining.
Once the gun is set for staining it is important to ensure that the dust from the wooden surface is fully been vacuumed out. The dust may collect or settle due to previous sanding and buffing activities on the wooden surfaces. Staining using spray gun must be initiated through edges of the product which then will be followed by the box coat against the grain the body of the wooden component. The Same technique of spray gun of overlapping for about 50% will be used for staining through Spray Guns. The staining technique is very important to achieve a right symmetric color in the finished product. For the lighter color, one may choose to flash the gun with air through the spray gun post first layer to dry the stain coat immediately. For a bit, darker color one may choose to allow some time for the stain to settle on wood for some time. Multiple rounds of coats can be applied on the surface of the wood as needed. Darker shade demands up to go for multiple rounds until we get a comparative thick coat on the wooden surface. There are advantages and disadvantages of both darker and lighter tone of stain on wooden surfaces. It goes with unique taste and preferences of customers and to match their interior needs. It is important to ensure that staining material is settling down into the molding profiles of the wooden surface. These molding profiles are the results of the routing activity we performed on the wooden product. Non-settling down of stain paint in the molding area may result in a cyclone effect which will cause shadowing around the profiles of the surface. On other hands, we also must ensure we bring consistency in shade and avoid over the settling of stain color on the molding edges. Too much material coming out of the gun for molding edges result in pooling on the edges which will cause dark lines along the surface.
In other cases, to stain a specific wood we need to have a stainable filler which may be solvent base or water base. A pigment needs to be mixed with these natural color fillers to match up with the wood color for consistent finishing. We also have oil based paddies available in the market in different final color which can be mixed together to achieve the desired color.
If things go wrong while putting stain coats on the wooden surface, one can use lacquer thinner to wipe out the wooden surface to start it over again. There might be multiple reasons for things to go wrong, as an example suddenly gun may leak for some reason. It is important to keep our spray booth out of dust and be equipped with related infrastructure such as right speed exhaust fans to maintain moisture in the environment.
We generally use Epoxy based sealer before giving a final coat of epoxy polish on the wooden products. Epoxies are from the family of polymer compounds are polyurethanes. Usually, these epoxies based sealants and final polishes work as waterproofing (I will say rather resistant). The epoxy coat acts as protective coat from the environment, water and once in place would stay there indefinitely. The advantages of using epoxy as a base are that they are VOC free, thicker for a quicker build, do not require a primer on good clean surfaces. They are also the ideal base coat for surface coatings. Epoxy based finished set virtually at any temperature, winter, and summer. These bases are nationally and internationally approved which works as the base for scratch proof wooden surfaces. Off course, deep impacted scratches cannot be avoided on these surfaces as in any other coats. Epoxy based finishes usually bring good flexibility and resilience and will never become brittle. More importantly, sealing the wood with an epoxy moisture barrier dramatically lessens its stretching and shrinking. Epoxy coating benefits by getting the protection from UV radiation that it needs. Two to three coats of epoxy also provide a stable base for clear two-part polyurethane finishes.
Epoxy sealers mixed with thinner provides required fluidity to make it ready to spray. Epoxy sealers and final polishes come with thinner and hardeners. The thinner helps to make the base coats fluid and sealers help to stabilize the material. The spray pressure to these sealants is usually kept on the higher side which ensures the penetration of sealant into the wood surface. The sealant viscosity plays the key role as well, bit thicker coat creates the good layer on the finished wood. Sealants are transparent in nature which may turn into milky white depending on the moisture content of an environment during the spray. The milky white effect due to moisture can be easily avoided by maintaining the moisture content in the spray booth. Usually, it takes 4-5 hours or a day to dry one coat of sealer which may vary depending on the weather conditions, spray area, conveyor system etc.
Base coat of sealer will be followed up by sanding (only after fully drying of the coat) using higher grade sanding papers. The sanding posts coats of sealer ensures the smoother surface of the wood. Slight uneven surfaces post sealing will be removed by using of sanding post sealing. We usually recommend two coats of sealing which will ensure a good control layer between wood and external environment.
Sealing after staining helps to protect the stained color applied on wood prior to sealing. Staining helps to penetrate the color into the wood grains and pores which will be filled through sealing. This ensures the staining color enters the pores of the wood and stays there in protecting against the environmental changes. This will also ensure that extraction or contraction of wood doesn’t impact the final finishing of wood. Protecting wood is important for products used outdoor or indoor in home or office.
Final polishing is achieved with the highest quality post-staining, sanding & buffing processes are been carried out under strict supervision with no tolerance towards final quality. All preceding activities such as Machining, Routing, Sanding, Buffing and staining leads towards an ease of final coat of finishing on wooden surfaces. This, in turn, will help us to achieve our goal for old or new wood, look beautiful and protect from environmental variations.
The final wood polish on wooden surfaces comes into two combinations glossy or matt finishes. We usually prefer a combination of both or more towards mat finish which helps to get a required decent looking finishing. The final finishing depends on the type of product as we use glossy finishes for garden benches and some of the wooden components. Whereas Matt finishing suits for the best looking elegant doors and windows. Our symmetric consistent looking finishing helps to bring an elegant look for our products.