Lacquering - what am I doing wrong? (dips)

[mr_push_pull]

Hi all

I'm using a brush to lacquer my new mahogany-veneered boxes, but I'm getting a lot of dips after the lacquer dries. I used 10% thinned lacquer for the first layer (as the instructions on the lacquer can say), and unthinned for the second layer. The first layer was completely absorbed by the veneer so I didn't sand it, but I sanded the second layer. For the third layer I used thinned lacquer again (more than 10% thinner) as someone on this board recommended, to allow the lacquer to even. But as it dried, dips started to appear. What am I doing wrong? Is the lacquer too thin, or what?


Thanks,
Mr. Push-Pull

[richie00boy]

How long did you leave between coats? Possibly not long enough. I think it was a mistake to thin the third coat as it seems to have reacted with the second unthinned coat.

What glue did you use to bond the veneer? Maybe there is some reaction with that?

Are you using the correct thinner? There's different types of laqcuer/paint systems - cellulose, acrylic etc.

[ShinOBIWAN]

There's not much you can do about the dips, its part of the wood/veneer your using. What your seeing is the laquer effectively shrink, something common with all solvent based paints, and reveal the imperfections.

You've got a couple of options:

Apply copious amount of laquer to effectively level the surface and then sand flat.

Fill the depressions but possibly make the veneer look terrible depending on the grain and pattern.

Live with the natural look and sacrifice the gloss finish.

[mr_push_pull]

Originally posted by richie00boy
How long did you leave between coats? Possibly not long enough. I think it was a mistake to thin the third coat as it seems to have reacted with the second unthinned coat.

I left the lacquer to dry for 2 or 3 days between the second and the third layer. It didn't stick to the sand paper so I assumed it had dried. The instructions say 24 hours drying time.

Originally posted by richie00boy
What glue did you use to bond the veneer? Maybe there is some reaction with that?

I used PVA to bond the veneer.

Originally posted by richie00boy
Are you using the correct thinner? There's different types of laqcuer/paint systems - cellulose, acrylic etc.

The istruction say to use thinner for alchidic paints/lacquers, and that's what I used.

Originally posted by ShinOBIWAN
There's not much you can do about the dips, its part of the wood/veneer your using. What your seeing is the laquer effectively shrink, something common with all solvent based paints, and reveal the imperfections.

So the shrinking should be less severe with unthinned lacquer, right?

Originally posted by ShinOBIWAN
You've got a couple of options:

Apply copious amount of laquer to effectively level the surface and then sand flat.

Fill the depressions but possibly make the veneer look terrible depending on the grain and pattern.

Live with the natural look and sacrifice the gloss finish.

In this case I think I'll try a fourth layer on the back of the box (unthinned) after sanding, and see what happens.

[richie00boy]

Good luck, let us know how you get on. I have a veneered box to do and I'm wondering if an oil-based finish would be better.

[pinkmouse]

It may well be due to surface contaminants on the veneer. When I used to used oil based finishes, I would always wipe over the surface with acetone before application.

[ShinOBIWAN]

Originally posted by mr_push_pull
So the shrinking should be less severe with unthinned lacquer, right?

Not really, thinning is just to make the laquer flow better on application and is mainly used for spray applications. The shrinkage is caused by the paint losing mass as the solvents are released during curing/hardening. Even a rather thick coat will shrink significantly after a month or two, revealing the depressions once again. Its the reason why joints reappear whilst painting MDF, that same thing will happen here. However, enough applications will see this effect lessened to the extent thats its invisible to all but the most concentrated examination.

[lufbramatt]

Originally posted by pinkmouse
It may well be due to surface contaminants on the veneer.

I agree, I've seen a similar effect when the surface (styrene in my case) had been contaminated by silicone mould release agent and I had neglected to clean the parts properly.

I think i would leave the job a couple of weeks to sit and see if it is going to react any more before I'd put any more layers of laquer on, then make a decision as to wether to sand back to the wood or carry on.

[mr_push_pull]

The only thing I can do is see what happens after a fourth unthinned layer, I think it can't be worse than this. All sides already have 2 layers of lacquer and this doesn't leave me with many options. Anyway, it doesn't look that bad from the distance

[richie00boy]

Maybe strip the lacquer with Nitromors, but that may affect the veneer glue so could be risky.