Filling grain

Basic methods for filling grain and finishing. April 9, 2003

What should we use to fill grain without losing the grain when finished, especially on oak and grainy woods? Maybe just more coats of lacquer and sanding between for those who want a smooth surface. I'm a woodworker and not much of a finisher.

Forum Responses
(From WOODWEB's Finishing Forum)
From contributor M:
When you say, 'to fill grain without losing the grain when finished'.

1) Do you want to add color only in the grains?
2) Do you want to add color and also fill up the grains?

Whatever you decide to do, the grain will add some kind of color to it, even multiple coats of water white material. To fill the open grain of porous woods such as mahogany, oak or walnut, professionals use what's called paste wood filler. It isn't that difficult. You can buy it in quarts or gallons, pure white to pure black. It also comes colored and goes by such names as brown mahogany or dark walnut and they even have one that's called natural. You will also need a chunk of burlap, some Naptha, an empty can to mix it up in and a stir stick to stir it up. These products are readily available in any good paint store and won't cost you an arm or a leg. There are many products that finishers use to fill the grain but paste wood filler will do a good job for you. For the best results possible, be sure to follow the directions.

From contributor M:
There are times when a paste wood filler is needed to do certain types of finishes. This is when you want to add color to the grain and also fill up the grain to be level with the top of the wood. This finishing technique is mainly used when you want a piano type of finish, where the grains are all filled, and your coatings are above the wood's surface. It is used mainly to add color and to eliminate extra coats.

If you are only looking to accentuate the grain with color and not fill the grain, and yet have a natural clear finish, I can tell you how you can do it. This technique is much easier to do than using a paste wood filler.

From the original questioner:
We just have the occasional customer that wants "filled mahogany" or no visible grain marks showing. They do expect to see some grain showing through the finish. I will try the paste fillers on a few samples to see if that's the solution.

Why don't you use a clear waterborne paste wood filler like Target's HSF5100? I don't particularly like the look of brown solid stuff filling the wood grain. Actually, before I knew there was even a product for filling grain, I just sprayed about 30 coats of finish to fill in the mahogany grain (I had lots of time on my hands for that project).

I think the questioner just wants to know how to do a partial fill finish. You can do it with 2k urethane, which will give you any degree of grain filling you want. Or use paste wood filler, which you can tint to any color and it will enhance the wood grain and fill it at the same time.

Professionals use many different methods of filling grain, depending on their finishing techniques, materials and the looks they want to achieve. Paste wood fillers are but one method of filling.

If the questioner decides to go with the paste wood filler method, how can he avoid what we call "gray pore"? Even major manufacturers have to watch out for this finishing defect.

It is the issue of avoiding gray pore that may mean the use of MLC's AC Sealer will work better for Glen. Maybe, maybe not.

You avoid greying by allowing all solvents to evaporate before proceeding with the next step. The next step could mean refilling or pisscoat sealing. Not all do, but I allow two weeks for filler to dry before proceeding. Also, buy the best paste filler you can afford.

From contributor M:
1) Seal the woods.
2) Apply the paste wood filler.
3) Start scraping off all the excess filler.
4) Apply your clear coats.

Once you use polyester, I can almost guarantee you that you will never again use paste wood filler. Blow it on, grind it off, topcoat with 2K urethane and you've got the best looking, most durable finish the world has yet developed. It's a thing of beauty.

I have had to paste fill many full size slab doors (10 footers, too) of many different species of mahogany. What I have found works best for me is the following schedule:

Pre-wet door with water and steam out any dents and scratches.

Orbital sand with a *strong* light at a low angle to the door surface. (I have door carts which allow me to hand the doors on pins to rotate and spray both sides of the door at once without standing.)

Spray on water stain to point of puddling (usually some blend of Lockwood #57) and wipe off completely.

Allow water stain to dry completely. (In my area, Nevada, about 1- 1.5 hour. To find out your drying time, I recommend a moisture meter.)

Spray on a wet coat of vinyl sealer thinned 3:1 (thinner/sealer).

Scuff sand 320 and apply paste filler. (I use Sherwin Williams thinned 150% with VM&P Naptha Tint as needed.) Wipe it into the pores very well until it starts to flash off (turn dull). Then I use a silk screener's squeegee to squeegee off the excess filler right back into the can for the next door. Use a clean rag to wipe off what little bit is left on the door, being careful not to wipe any out of the pores. Allow to dry. Sherwin Williams says 4 hours, but I wait overnight.

Spray on a full wet coat of vinyl sealer and you are ready to continue with a CV or pre-cat schedule from there on.

The process outlined above can be used for many finishes, not just CV or 2K. I used the same procedure back in the good old nitro lacquer days. Just substitute sanding sealer for vinyl sealer and you're good to go.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
As an alternative to paste filler, I often apply three good coats of water white lac. Allow this to dry overnight. Then I cut back the finish using a scraper or razor blades. This takes practice to perfect but it's real effective. After cutting back, sand with 220 and work down to steelwool 0000. Repeat these steps until you reach the fill level you're looking for. I like to finish this off by hand rubbing the wood with steel wool and pumice stone.