Bubbles in NC lacquer

**Arron** · 28th August 2013, 11:57 AM

If you look up or down in this forum you'll see a thread by me on pullover mixes - with a nice definition contributed by another forumite. Basically, its a hand-applied mix that softens and repositions the lacquer after its been sprayed on. My understanding is that it can be applied in one of two ways:
1. by process, across the entire surface. You would do this to get a piano finish (ie dead flat mirror finish). In other words, you are using the softened lacquer to fill the grain. You would do this somewhere before the final coat. Just pull across the entire surface till you have pushed softened lacquer into all the pores.
2. as a spot repair - either during the spraying process or after.

I don't really use method number 1 because I don't want a piano finish. My reasoning is that with most things in the world today looking like plastic I don't want to make my woodwork look like plastic too. Hence I want the grain to telegraph itself through the finish. It probably looks like I would like to get a piano finish but just don't know how to, but I don't mind that. I think a lot of the finishing techniques we hear about originated in the 18th century when there was no plastic to look like, so they didn't have this concern. Having this preference is convenient because whatever process you use to fill grain it is boring and labour intensive.

I do use method number 2.

A couple of other things I have thought about here:
1. lately, I've taken to attaching a second gun while spraying - a touch up gun which I fill with straight lacquer thinner. My idea is to pick this up and spray it across any faults which might appear while I'm spraying, allowing lacquers wonderful tendency to sort out all problems underneath to work for me. I've only used it once when I had a droplet of drool fall my respirator (I must keep my mouth open without realising it) into my work. I removed the liquid, rubbed it flat with my finger and then hit that spot a couple of times with the lacquer thinner before carrying on with a couple more coats. It worked in the sense that it flattened the mess out enough to allow me to fix it during the buffing process. It certainly beats having to sand flat and start again which is the only other solution I can imagine. Anyway, it may be useful if you are repairing bubbles by pulling - give it a localised spray of lacquer thinner, then put it at the bottom of the queue to flash off while you carry on spraying other things.

2. I find nc sanding dust is a good grain filler. When I sand something, say after applying a couple of coats of sealer, I used to clean it down completely before carrying on. Now, I leave the sanding dust in the grain, and just blow the corners clean. The next coat softens the dust and it becomes lacquer again, but deep inside the grain. Obviously you don't want grit or wood dust, but nc dust is a good filler so why waste it.

I should also point out that I have chronic RSI, so I have an aversion to sanding or hard rubbing that probably doesn't make a lot of sense to most people.

cheers
Arron

**John Samuel** · 29th August 2013, 09:20 AM

Managed to patch up two of the problematic panels. The third I sanded back to timber and started again.

Put on a thin coat of sealer, followed by a full coat. Sanded back ... looked OK. Applied another coat of sealer and sanded back again (trying to prevent build-up to too thick a film). By now the grain is all but filled to a smooth flat surface, but I applied another coat of sealer ... and got a couple of bubbles.

Bother, spit and darn!

Sanded the bubbles out and put a small amount of sealer on a can lid and continually worked it with a small brush until it was goopy, then applied this thick material to a small area around the bubbles. That worked. Lacquer went on fine without bubbles. Next time I'll try making up a pull mix.

Sometimes I get pin holes that do not emit bubbles. These are generally easy to fix, I "spot spray" the pinholes to fill them with lacquer and immediately spray the entire panel. Now that I am using slower thinners this seems to work fine for pinholes that are not emitting bubbles.

What I really want to do is to solve the problem of bubbles by effective sealing at the outset. Maybe I'll try two thin coats of sealer at the outset ... maybe not.

I've never had bubbles when spraying with poly or acid cured (high-build) lacquer. Is this what others have found?

**foxhound** · 3rd September 2013, 10:13 AM

Try some sil drops in your lacquer mix you only need two of three drops.You may have a problem with silicone.Worth a try and won't damage your coat of lacquer it will clear the problem up in a flash.

**John Samuel** · 3rd September 2013, 10:31 AM

Originally Posted by foxhound

Try some sil drops in your lacquer mix you only need two of three drops.You may have a problem with silicone.Worth a try and won't damage your coat of lacquer it will clear the problem up in a flash.

Thanks for that.

However, I doubt the issue is silicon. I have watched the bubbles forming under wet lacquer in the grain, and then rising to the surface and erupting. Still, if the problem persists, I'll try it.

**rustynail** · 3rd September 2013, 12:05 PM

When the bubbles are grain orientated it usually turns out to be silicon.

**John Samuel** · 4th September 2013, 12:17 AM

Originally Posted by rustynail

When the bubbles are grain orientated it usually turns out to be silicon.

Thanks Rustynail and Foxhound,

I was not aware of that. I have been careful to try to keep silicone out of my shop with one exception, the silicone sealant used to seal my dust collection system. Lubricants, polishes etc containing silicone are banned from the shop.

Did a search for sil drops. Only found a reference to Silastic Replicating Resin (SIL-FLO) and brazing products. Can anyone help me understand what sil drops are and where I can get them?

**Arron** · 4th September 2013, 07:39 AM

Originally Posted by rustynail

When the bubbles are grain orientated it usually turns out to be silicon.

I would have thought that if the issue was silicon contamination John would be getting fish-eye rather then bubbles (fish-eyes = round bare patches where the finish fails to adhere). How does silicon contamination lead to tiny enclosed bubbles arising deep within the pores?

Cheers
Arron

**foxhound** · 11th September 2013, 12:56 PM

Hi John,

Sorry for the late reply but you should be able to get the sil (silicon) drops from a panel beaters shop or the likes.The last time I purchased a bottle it was from Wattyl.

**John Samuel** · 11th September 2013, 05:57 PM

Thanks Foxhound,

I'll try it and see what happens.

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