High gloss finish on mahogany

Techniques and products that yield a mirror finish on open-grained woods. October 9, 2002

How do you get a closed pore finish on mahogany? I have been trying for a long time without success. I would sand the sealer flat, no pores showing, and when I put the topcoat on, the grain would appear again. I am looking for a sprayable solution instead of sand and buff. Any advice?

Forum Responses
You didn't say what you were using. I would use a self-seal conversion varnish or go up to a higher-end product, like a two-part polyurethane base coat and two-part polyurethane topcoat. If you are staining the wood, you can use either a filler stain or filler glaze stain to help fill the pores.

From contributor A:
PianoLac is expressly designed for this type of finishing. It's easy to use and tech service from an experienced pro finisher is available by phone and email.

From the original questioner:
I have used CV and had some good results, but how long should I let the sealer coat dry before I put on the topcoat? I have tried your idea of seal then put down the stain with the paste, which works real nice.

I have looked at the PianoLac specs, and waiting 3 to 10 days to polish would put me out of business. My jobs are always "hurry up and wait" or "I want it yesterday." I just need something fast. I usually build then finish in a small shop, so I would need a system that will keep me working till I get it done. In a small shop, I can only do one thing at a time - build or finish.

You'll never get a true mirror finish if you can't convince your clients that they have to wait a while. All finishes shrink until they're fully cured, including postcats. Even if you level everything perfectly, the pores will reappear as the film shrinks up. Some things just can't be rushed.

I believe that the traditional method is to use a filler to seal the pores first and then stain and spray after sanding the surface flat again. It's a bit messy, but you are starting with a flat surface instead of one poked full of holes. You can even use a colored filler, though dark brown or black is most common. Same technique for any other porous woods like oak or ash. Try a blue filler on ash for a really different look.

Your only solution is to use either polyester or a 2K urethane. Polyester is my preference. You will still need to wait 3-4 days after putting the polyester topcoat on to allow for shrinkage.

M. L. Campbell makes a catalyzed filler for uses like this. It's called A.C. Sealer even though it's for filling, not sealing. Catalyze the product 10% with their catalyst (before adding reducer). Reduce to spray viscosity, which is usually about 20 seconds with a Ford #4 cup. Spray on. Sand back to the wood flat in about 20 to 30 minutes. You may need a second application.

This MLC product is meant to sit in the wood pores, not on top of the wood. This is unlike the polyester and 2-pak urethanes which can be built up on the wood and then topcoated.

And you should apply your wiping stain before applying the A.C. Sealer. What that means is that you have to do some practicing so you will get a feel for how much to sand off and when you have sanded too much off (leaving you with sand-throughs in your stain coat).

Within about 40 minutes of applying the A.C. sealer you are ready for topcoats. Is shrinkage still possible even with the use of the A.C. Sealer? Yes, but it's very little.

I have a friend from Oregon who uses Duravar (a catalyzed lacquer) in such a way that he gets no shrinkage and he completes his spraying the same day, ready for rub out soon afterward. First, he uses Martin-Senoir's Acrylic Enamel Reducer (only 20% by volume) for the Duravar instead of the MLC suggested reducer. Second, he starts out with his filling by spraying dustcoats and light sanding. Then he sprays his full wet coats. He has repeat customers, no call backs and years of experience. But before I suggest that anyone try this maverick approach to using Duravar, you ought to have him detail you the steps himself.

In all this, I think that without big drying ovens for you to use, you have to rely on the passage of time.

From contributor A:
Allow me to clarify the time period needed to cure PianoLac for rubbing. If you are going for the ultimate in mirror smooth, high polish finish, three-day cure is advisable, unless you can arrange to have circulating warm air blowing across the work piece. This can be as simple as a forced hot air heater, or just leaving the heat on overnight with a fan blowing around the surface.

This procedure will release remaining solvents and cure the coating, ready to rub.

If you've been spraying thin coats and filling the pores as per the advice on the website, shrinkage will not occur. This may seem an outrageous claim, but I have finished over 20 grand pianos, most of them Steinways, for very critical customers, with PianoLac. I followed up on them in the customer's home, and there has never been one instance of shrinkage.

The right way to do this, in my opinion, is:

After staining, use a 2K urethane isolator.

Polyester grain filler. Grind down with a random orbit sander. This is the best grain filler on earth. Nothing else is even close.

Either polyester or 2K topcoat. Grind down with fine paper and ROS.

Automotive rotary buffer and compounds to high gloss.

I know that this works and is permanent. This system is completely devoid of thickness limitations. Put it on as thick as you want.