Sanding Imperfections out of a High Gloss Finish

Advice on equipment and hand methods for sanding a polishing a "Euro wet look" finish. July 25, 2010

I have done a project using MLC euro wet look on large 4x8 panels of zebra wood. I did a closed pore finish that we sanded and buffed to high gloss. The problem is that the panels look wavy (rippled). What would cause this? We sanded from 400 to 3000 grit then buffed with machine, but can't get rid of the waviness. The panels were factory laid up on 3/4 MDF.

Forum Responses
(Finishing Forum)
From contributor A:
Wide belt sander marks?

From contributor T:
What type of equipment was used in between coats, orbital or straight line sanders?

From the original questioner:
I do not think they are wide belt sanding marks. And we used orbital sanders, 6".

From contributor G:
Here are a couple responses from this Knowledge Base article:
Eliminating Waviness in a Polyester

"Take a straight edge and see if the surface is flat. I suspect that the plywood was a little wavy. You would have to have some really crazy grain to cause this problem. I suspect you used a 6" random orbital to sand from 150-400. If there is a wave in the substrate the 6" disc will not remove it."

"The plywood substrate must be as dead level as physically possible before spraying anything. Block sanding by hand is one way to do it, but you can save hours of time and much joint pain by using a straight-line air sand with hard felt pads (not rubber)."

From the original questioner:
Yes, the wood was level prior to any finishing. It was run through a wide belt then sanded prior to paste fill. I am about 7 dry mils. I did use air orbital sanders through the process then buffed with 10" buffer. Can I resand with flat line and only rebuff out or do I need to resand with flat line, recoat, resand, and buff?

I am in Las Vegas. Where would I find a flat line sander with felt pad?

From contributor W:
It seems that your unfinished panel was not even when you started to finish it. Or the grain pattern may have caused the wavy look. With high gloss finish, the uneven surface is more visible. You can fix this problem with the coating material. You need good preparation of the unfinished wood.

From contributor R:
Do you have a good wide belt sander that you can sand the panel with now (one made to sand finishes)?

From contributor Z:
Very difficult for 4x8 plywood in a widebelt sander. If zebra was on MDF or flake, you probably would have a different result.

From contributor B:
The waves you're looking at are from the defects in the substrate. When producing high build/high gloss finishes, it is crucial to machine the surface with an inline sander or run them through a wide belt sander prior to spraying the topcoat. It will make no difference if the veneer is on plywood or MDF.

I would forget about trying to level out and then re-polish. Level the product out with an inline sander and 220 grit. Then remove the 220 scratches with a six inch orbital and 320 grit. Then spray a new coat of urethane and polish. If you applied stain on the zebra wood, you need to be careful not to sand too far when leveling. If you sand too far you will remove the stain and that will be a big problem. A better choice for this project would have been a polyester sealer with a high gloss urethane as a topcoat. Less labor, less shrinkage, better durability, and higher quality.

From contributor R:
We sand table tops bigger than 4x8 feet no problem. It just depends on what kind of sander you have. There are many wide belt sanders designed to sand finish. I like to spray polyester and sand through the wide belt before spraying the 2k urethane. (The top is always white wood sanded through the wide belt too.)

There will always be a little ripple to any hand sanded and buffed top. The perfect ones are sanded and buffed through a dedicated machine. It's like hand rolled glass - I prefer the defects from hand craftsmanship.

From contributor S:
Contributor R, what spray equipment are you using for your polyester? And how big of a wide belt sander do you use?

From contributor D:
Contributor R, I recommend you try the new purple 3M Trizact P1500 Clearcoat Sanding Discs. These are always used wet and last a lot longer than 260L. Another advantage is that the discs are perforated with a million tiny holes and do not vacuum stick to the work like wet 260L does.

From the original questioner:

Thanks. I am purchasing a double pad inline sander that I can use dry or wet. The other problem I was having is in the final buffing, you can see swirl marks from the buffer. What can you recommend?

From contributor D:
The swirl marks are completely normal if you're using a wool compounding pad, which is what you should be using to start with. The solution is a black foam pad and Menzerna 106FA polishing compound. A couple passes with these and they will be gone.

From the original questioner:
Who makes Menzerna 106FA polish?

From contributor D:
Menzerna. This is a German company that makes the best polishing materials in the world. They are on the web.

From the original questioner:
Thanks for the info on polishes. I ordered their product. What about sandpaper? This type of finishing is very time consuming, and any advice to cut labor back would be helpful.

From contributor D:
Here's the deal. You must start with something aggressive to flatten the surface, and a hard and flat sanding pad. I normally begin with 3M 260L finishing film in P800 using a 3/32" orbit random orbit sander. (My personal favorite is AirVantage.) You must continuously clean the paper with a fingernail brush to remove any corned finish as these corns will cause deep scratches. 260L is expensive and you're going to use a lot of it.

After you've got things flat, you go with a softer pad (what 3M calls a "painters pad" and P1200 to remove the P800 scratches.

Prior to the new purple Clearcoat Trizact discs, you'd use P1500 260L, but now with this new innovation, use this P1500 Trizact paper wet. It lasts a long time, much longer than 260L dry.

Finally, use a P3000 Trizact foam pad wet on a large orbit random orbit sander. The $29.95 Campbell-Hausfeld sander they sell at Wal-Mart works well for this purpose. The surface should be quite shiny after the P3000 Trizact.

I use Menzerna Power Gloss with wool next. This will give a high gloss surface but you will have swirl marks. 106FA and black foam and you've got a mirror. End of story.

General rule of thumb when polishing: this should go quickly. If it doesn't, you need to sand more. Most people buff too much and sand too little. If it's sanded properly, the buffing shouldn't take very long.

From the original questioner:
Thanks. I ordered a Detroit double pad inline sander and all the rubbing compounds and liquids. Since I am using an inline sander, whose sandpaper should I purchase and what type, as it takes sheets? And do you think I should sand with orbital after inline sanding?

From contributor Y:
Reflection and refraction are not the same thing. Polishing procedures affect surface reflection. Refraction is caused by the number of layers of coating and type of coating. With acrylic polys, each layer is a barrier. This causes refraction when light reflecting from each layer takes a different amount of time to reflect back to your eye. Itís like putting a pencil in a glass of water and seeing the pencil bend. With enough layers, youíll get wavy lines even though the surface reflection may be excellent.

From contributor N:

Zebra wood is a semi open pore wood. In our factory we use Melazi wet look the first four to six coats of the build we put down, let dry and sand with 6 inch sanders to 180. Next we close the pores of the wood with full strength build. The problem is the way you applied your built coats.