Lacquer Dipping - stress fractures?

[Sawdust Maker]

Gidday all
Went to assemble a couple of pens yesterday
They'd been dipped (5 - 7 times) and hung in my heat box to cure after each dip
Then the ends had been squared off to stop or negate chipping
Then they had been placed on my rack to await assembly

When I checked them to see whether they needed sanding or buffing I noticed that each had developed fractures in the lacquer

None of these has been assembled so it's not the fittings going in crooked

One had to be sanded a bit - 600 grit then micromesh then polish with brasso



Any ideas anyone why this could be happening or what could cause it?

Thanks in anticipation

 

[titan2]

How did you square them off? Looks like it may of come from that last activity........


Barney

 

[schafergroup2006]

it really looks like wood movement. could it have been heat build up from squaring the ends?

 

[schafergroup2006]

other than the cracks those have a beautiful shine on them. like glass

 

[Sawdust Maker]

How did you square them off? Looks like it may of come from that last activity........


Barney

Very carefully - with hand held fine sandpaper initially then with sandpaper on a flat surface. Doubt whether any heat build up during this process
They looked fine after the squaring off

We've had a couple of fairly hot days here recently, was wondering whether that could have an effect

 

[helgi]

How hot was your heatbox when we finished a top on a writing desk one of my co-workers thought he was going to do me a favor by playing a heatgun over the top you should have seen the fissures and cracks in that top. Problem with laquer when drying to fast with heat it shrinks to fast and the top dries to quick and won't follow the underlayer therefor the cracks. Only thing to do is strip them and do again as the cracks will go right down to the wood. You can try sanding and refinish but take a close look at them as any hairline crack will split and chip as laquer is a hard finish.
helgi.

 

[jttheclockman]

I think we are missing something here. I would blame heat if you dipped these right after you got done sanding to square the ends. If that is the case then that could be what happened. I also would blame the cracking on if you tried to sand the ends after they have been dipped to get rid of any drippings. It has to be a temp thing because laquer actually is a soft finish. Softer than poly. Then there is the preverbial wood movement. Being so thin on the end I am not going with that one. but it could happen.

Just read again your procedure and there is so many things wrong with that. The heatbox thing is not good. Lacquer is a fast drying product in itself and now you stepped it up. The layers do not have time to dry and cure. that stuff is not like automotive lacquer where you can use heat lamps. The next problem is you sanded the ends right after they were dipped and dried. They were not cure though so you added stress to the thinnest part of the lacquer base. Lacquer need to cure and not only dry. That is also another reason people do not get a nice shine on lacquered pens because they do not let it cure. I would rethink your methods.

 

[Russianwolf]

Are all the cracks on one side? My gut says the sanding on the flat surface is the culprit.

 

[jleiwig]

I would bet the heat box is the culprit. Lacquer needs no heat box to help it along.

 

[Sawdust Maker]

Thanks for all the comments, It is greatly appreciated
I should describe in more detail what I've been doing.
(and by the way I started trying this when edblysard posted his procedure on the Aussie forum sometime last year)

The lacquer I'm using is automotive, thinned 50:50 with thinners
I sand the turned blank to 600
I wax the bushes before putting the blank on.
I dip, hang and cover with a box. I've a 25w light in the box. I started doing this when I had failures last year - culprit was put down to weather being too cold and/or sanding too fine (I was micromeshing to an inch of its life)
24 hours later I dip again - before this dipping I check for any irregularities, if any, eg bubbles, I'll quickly sand out with a bit of 600 wet and dry.
In total, I'll dip 5 ish times over a period of a week, with 24 hours between each dipping.
Then let hang for a few days before removing from bushes. I score the lacquer about a mm from the end and then remove from the bushes. I then sand the ends using the 600 and then finer, I can't see this building up much heat. It's hand done by moving the blank on the sandpaper. Sort of turning it between my fingers whilst end is on the paper
If I've managed to get lacquer build up on one end I'll put the blank between centres and wet sand until it is within size.
In the photos above I don't think the cyprus pine (the lighter one) was wet sanded

So where is my technique failing me?
How long does it need to cure and at what temp or range of temp?
Is 24 hours between dips not enough?
How else could I be stuffing it up without realising?

I did leave these resting in the shed (shop) for about a week before I went to assemble and noticed the fracturing. It did get pretty warm here during that week ie over 30 degrees

Sorry about the long post but as you could imagine this is extremely frustrating.
What is annoying is that I've done a couple of other pens at the same time as these and they appear fine.

 

[Sawdust Maker]

Are all the cracks on one side? My gut says the sanding on the flat surface is the culprit.

The cracks appear all around the blank - some worse then others

When I've got the sanding wrong I've chipped the lacquer - also has happened when I've taken the bushes off

 

[RussFairfield]

You have just discovered why lacquer is the easiest finish to use, but the most difficult to use well.

For what its worth, I have never had any success using automotive lacquer on wood. Other have claimed success and that they use it all the time. I have never been able to do that. For one thing the solids content is too great as it comes from the can, and it needs more than 50% thinner. All of that thinner has to evaporate and that causes stress problems with a thick finish. Besides, the automotive lacquers don't have the flexibility required for wood, and that causes cracking and crazing problems.

Having said all of that, you might want to use a Deft or Watco lacquer that was designed for wood rather than trying to adapt one that wasn't.

Besides what others have said, 5 to 7 coats is an awful lot of any lacquer. I use 2 dipped coats of unthinned Deft straight from the can, one from each end to level out the thickness on the pen barrels, and that is more than enough.

Lacquer also takes time for all of the solvents to evaporate, and the thicker it is the longer it takes. You can tell by the smell. If it smells like lacquer thinner, it hasn't evaporated yet. You can also tell by rubbing your thumbnail lightly across it. It you leave a dent, it isn't ready, if you don't, it is. With my 2 coats of dipped Deft, I have to wait several days, and I make that a week for good measure before handling and trimming. I have no idea how long you should be waiting with 7 coats, but I would say at least 2 weeks for a start.

Forget the heat unless it is there to provide a comfortable 70-degrees in a cold freezing shop. Any more heat that that will cause expansion problems with the lacquer film, and the thicker the film, the worse the problems.

Finishing requires patience. You are trying to do it too fast.

 

[holmqer]

Besides, the automotive lacquers don't have the flexibility required for wood, and that causes cracking and crazing problems.

I am a bit curious about this since automotive lacquers are intended for metal parts which have a higher coefficient of expansion than wood (steel is 7.3, wood 2-3 microinches per inch/deg F) and are exposed to higher thermal stresses than wood (think of the temperature range of a car hood between winter to summer with the engine on, the hood of my car goes from below 0F in the winter with the engine off to hot enough to burn my hands on a hot summer day with the engine on)

 

[jleiwig]

I am a bit curious about this since automotive lacquers are intended for metal parts which have a higher coefficient of expansion than wood (steel is 7.3, wood 2-3 microinches per inch/deg F) and are exposed to higher thermal stresses than wood (think of the temperature range of a car hood between winter to summer with the engine on, the hood of my car goes from below 0F in the winter with the engine off to hot enough to burn my hands on a hot summer day with the engine on)

It doesn't have anything to do with expansion, it has to do with flexability as Russ stated. A solid metal panel on a car will not ever flex the same amount a small 1/16" or less thickness piece of wood will.

If you want to use automotive laquers, you would need to add a flex additive to it, commonly used on bumpers or other plastic parts to prevent cracking.

Depending on what finishing system your using, I think that would be silly because your really out a lot of money for negligible benefits over commonly used pen finishes.

 

[RussFairfield]

The combination of wood movement from both moisture content changes and thermal expansion is more than anything you will ever see in a piece of steel where only the thermal expansion is only factor. The wood in a table top will move 1/4" or more with seasonal changes in moisture content. That is tough duty for an automotive lacquer. .