Sunday, May 13, 2018

PU based finishes: Asian Paints Woodtech PU

I have experimented a lot with different PU based finishes. What I am going to describe below is my experience with Asian Paints Woodtech PU.

The reasons why I selected Woodetch PU

  1. Fast drying: Dries in about an hour. As I do not have access to a dust free location, the longer a finish takes to dry, the more dust gathers. Besides, I can put on one coat on one side, do something else and finish the other sides in a matter of about two hours. 
  2. The only finish available near me; Well I really do not have much of an option with regards to finish in my area, so I have been more or less forced to use PU. 

The other options

  1. Asian Paints Touch wood: This is cheaper. However it takes a longer time to dry, and therefore will pick up more dust
  2. Asian Paints Aquadur PU: Water based and very easy to use, and fast drying. However as it builds up it leaves a white milky hue, that I do not like. More about this finish later. 
What you will need
  1. PU Sealant : 1 Liter
  2. PU thinner/NC Thinner: at least 2 L 
  3. PU Woodtech Matte/Glossy 1L
  4. Small spoon
  5. Bowl to mix
  6. 2 inch paint brush 
  7. Waste cloth
  8. Bottle to collect waste
  9. Time
Application Procedure (How I do it) 

  1. Clean and sand the surface to be finished.
  2. If you are worried about insects, apply some insect repellant. I use Terminator (made by Pidilite). It is supposed to have some herbal extract that keeps insects away. This will need to dry overnight. Be liberal with this. 
  3. Apply Asian Paints PU sealant. Mix 4 parts of the sealant with one part of hardener.   I use a brush.  This has to be diluted about 1:1 with PU thinner. As PU thinner is quite expensive, I get away by using NC thinner. This dries rapidly. 
  4. If time permits and if you have patience to spare, sand with a 400 grit paper lightly and apply a second coat of PU sealant. The sealant takes about 1 hour to be dry to touch. It will be ready for the next coat after about three hours or so. I put on one coat in the morning before I get to work, one in the evening and one at night. Sand with 400 grit paper. 
  5. Mix 4 parts of PU varnish with 1 part of the hardener. Dilute this with about 1:1 thinner to get it to a consistency that can be painted. 
  6. Paint this on the surface. The varnish dries very fast. You may not be able to go over what you have already brushed on. Make sure there are no bubbles and drip marks. They will be a pain to take off later. 
  7. Let this dry for about to to three hours. Lightly sand with 400 grit paper and paint on the second coat. 
  8. Usually two coats will suffice. Stop when you are satisfied. 
Some precautions. 
  1. As the varnish dries very fast, the brush will feel sticky if your paint session takes more than 10-15 min. The brush may have to be cleaned with NC thinner in between.
  2. I usually collect the NC thinner and varnish that is wasted in a bottle rather than dumping it in the sink. 
  3. Make sure to clean the brush with NC thinner and the bowl you use for mixing. Wipe both clean after you use them. 
  4. You cannot get the varnish off with water or soap. Either use gloves or wipe your hands with NC thinner to get the stickiness off. 
  5. Keep some cotton waste cloth for this. Most of my old t-shirts end up as paint cloths. 
  6. The hardener and the PU varnish has to be air tight. I they are not, they will harden. 
  7. Although the tin says use the entire contents in one go, in reality for small projects I would need only a few tea spoons full of varnish. I use a small teaspoon to measure out varnish for small projects and a large 'sambar spoon' to measure out varnish for larger projects. If one is careful, you can use this tin many times until it is finished. 
  8. Keep sufficient NC thinner ready in case you knock over the varnish tin. Keep sufficient cloth ready if you knock over the NC thinner too. 
  9. Wear your old clothes. Staying away from curtains will prevent splashes of varnish on them and will promote marital harmony. 
Matte or Glossy?

I prefer matte. This retains the natural look of the wood, and after two or more coats, the wood actually looks as though it has not been finished at all. 
I do not like glossy. It finally gives a 'plasticky' feel to the finish. However many do not share my views and like a glossy finish. 

To stain or not to stain?

I do not like staining wood. It hides the nuances of the grain. However if it needs to be done, I apply either Asian paints stain or Sheenlac stains on the wood directly before I apply the sealant. Keep in mind that both the stain and the sealant are soluble in thinner. So as you apply the sealant, the stain may also change. Drip marks of the sealant  may contain the stain and may spoil the appearance. Once the sealant and the stain are dry, usuall applying varnish over this is not a problem. 
A scratch on stained wood, will be more apparent, as it will appear as an area without stain. In contrast a scratched on unstained wood, will not be so visible. 
Scratches on stained wood will need more care when varnishing. You may have to apply stain again. However scratches on unstained wood can be easily varnished over. 

Happy finishing!

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