My water based sanding sealer nightmare

My students are making 10 mahogany tables and a mahogany bar for a local restaurant. I went to HD to get sanding sealer and didn’t realize I got water-based. I hate water-based anything, but it said on the label it works with water- or oil-based Finishes. It was literally the last can of any sanding sealer they had of any kind, so this was my only option other than driving across the island, and we were behind schedule and the laser shop guy was going to be out. It had to be done today. Well, no big deal then. I am going to use an oil based varnish on top and so who cares if the sanding sealer is water based. (Inner voice: You’re about to make a mistake; water based stuff is worthless.). Me: Shut up, inner voice. I am not listening to you, even though you’re always right.

We put the sealer on before lasering our logo on the tops. The finish was really sloppy in the way it laid down, but it did dry clear and looked ok. I did notice that the normal iridescence of the mahogany didn’t show up as well, but it was done. All tops got sealed and went to the laser shop.

Yesterday I was exclted to get the top coats on. The very first one I noticed a problem. It looked hazy. I did one more and it was even worse. I ended up scraping it all off with a razor blade, sanding with 150 grit, wiping with denatured alcohol, then 220 grit and wiping with mineral spirits. That fixed the problem- basically removing all the sanding sealer.

I love Varithane oil varnishes, but their water based stuff I will never ever buy again.

Attachment 441437
It has a milky, greenish look. You can see where we sanded the logo lightly and it looks like mahogany should.

Attachment 441438



Here is the finished product after a full day of scraping and sanding ten table tops:
Attachment 441439

This customer paid us in full in advance and no way was I letting him get second-rate finishes.

This is the failed product.
Attachment 441440

A test panel would have shown the problem and saved you a lot of work. Why would you even need a sealer under an oil based varnish? Just thin the first coat or two.

John

Quote:

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Originally Posted by John TenEyck

A test panel would have shown the problem and saved you a lot of work. Why would you even need a sealer under an oil based varnish? Just thin the first coat or two.

John

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Hind sight. Sipo Mahogany is extremely porous. This project was behind schedule. I thought a sanding sealer would fill the grain better than thinned coats, and actually it did just that, but it didn’t stay clear. One thing positive is it did do a wonderful job of sealing the grain and the first cost of oil finish laid down like the third would have without the sealer. Sadly, it just looked like crap. The product said very clearly that it works with oil and water based finishes. I should be able to trust Varithane to have tested that already.

If it's available where you are get some Sealcoat shellac. It's the universal sealer and can be used under almost anything. Dries in minutes and helps accentuate the grain, too.

John