Spraying lacquer

[garfield]

Hi all,

I'm wondering if someone can help me please, with some advice.

At the moment I'm applying a coat of lacquer to some ply that I have made into a camp kitchen and I'm spraying it on. Now I don't know if it's me or its the spray gun I'm using - or even if I'm stuffing the batch, but when i spray it seems when i look at the job in the right light after spraying it that some parts of the wood is dry and other parts seem to have a good coat over it

So i didn't know if I'm not working the spray gun properly(can't see that being it though, it's not that hard), or I'm not mixing the lacquer properly with some metho to thin it out (i was working on 10% roughly) or if my gun is just that poor that it can't spray it properly..... does anyone have some advice or a theory please.

[munruben]

Couple of reasons come to mind. firstly holding the gun at the right angle is most important. Hold the gun facing the nozzle directly at the workpiece and keep the wrist straight while spraying. Try to keep the gun held at a constant distance from the workpiece and spray right off the end of your work. Don't stop spraying while you are over the workpiece, keep the gun moving all the time. Don't flick your wrist or fan the gun, this is a major reason for the problem you are experiencing. Hold the wrist firmly and straight.
Start spraying before you are over the workpiece bring your gun over the workpiece while it is actually spraying and continue and only stop spraying when the gun is not over the item you are spraying.
Fanning the gun causes over-spray on your work and will cause dry patches and a sheery appearance. So although it may seem simple to spray it does take a while to master these techniques
Regulate your pressure until you have a nice even, soft flow of material, if your pressure is too high it can cause blurring of the surface and orange peel appearance in the finish. This happens if you are holding your gun too close to the work with too much pressure.

Another thing to consider is how porous the timber is that you are working on. It could simply be that the wood is absorbing the material and just needs several more coats to get an even application. Timber has porous spots and some spots are more porous than others and therefor the material will soak into these porous spots and dry dull where the not so porous spots will not absorb at the same rate and the material will stay shiny.

Some of these problems can be corrected in your finishing process. Cutting compound or light sanding for instance and then polish with a good furniture polish can work to bring it back to a nice smooth even glossy finish.

The sponsors of this forum have excellent products for this purpose. You might like to take a look at some of their products.
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[garfield]

its funny you mention that about the regulator.... i notice when i spray my gun that the contents seems to spit out like it's blocked. it sort of sprays out like it has a blockage, but i know it isn't blocked. so that comes down to my gun and com[pressor not being regulated properly? at the moment i don't have it regulated and its up high.

[RETIRED]

its funny you mention that about the regulator.... i notice when i spray my gun that the contents seems to spit out like it's blocked. it sort of sprays out like it has a blockage, Probably has an air leak around the needle. Check the gland nut.

but i know it isn't blocked. so that comes down to my gun and compressor not being regulated properly? at the moment i don't have it regulated and its up high.

Without knowing which gun you have it is hard to say what pressure you need.

What sort of lacquer is it that you are thinning with metho?

There is a lot of info on the board about spraying. Use the search engine above.

[garfield]

It's just a standard spray gun i think.... it's not one of the gravity feed guns - although i wish it was

so basically I'll just spray some through my gun and muck around with my regulator until its a nice consistency coming through..??

[durwood]

You are doing at least two things wrong.

1 Use the correct thinner not metho it will mix with the lacquer but it dries too fast so thats why you are getting such a lousy finish.

2 You need at least 50% thinner more is even better 60% thinner 40% lacquer.

Put on a coat leave it for abnout 10 minutes repeat till you have 5 coats on.

Read Munrubens instruction and if it still is not workuing get back to us.

[garfield]

2 You need at least 50% thinner more is even better 60% thinner 40% lacquer.

Put on a coat leave it for about 10 minutes repeat till you have 5 coats on.

So I should use proper thinners with the lacquer then..?? I was once told by someone I could use metho too.... You know what though - ever since I have, I've always had a sh@t finish! It makes sense that it is drying very quickly too. Today I came home gave my project a light rub with 240 grit sand paper then done the same as yesterday - I added a touch more metho and sprayed my job. While I was moving the piece I just sprayed, it seemed that it had dried on the nozzle or something, and it was shooting the stuff out in like blotches... it seemed to me it felt too thick, so your 60%thinners and 40%lacquer sounds better

So 10 minutes between coats roughly so it is dry, and give it about 5 coats.

[addo]

It's ready for the next coat when the surface has pretty much returned to ambient temperature.

Can you spring $80 for a digital infra-red thermometer? Then you just shoot the wall temperature, and the job temperature. Couple of degrees won't kill you, but since evaporation of solvents will cool the job, temperatures do dip a lot lower just after applying.

I tend to use fresh Dulon "AAA Normal" thinners for most acrylic and nitro finishes. Metho in lacquer is a disaster waiting to happen and any thinners need to be newish; stored in a sealed container.

Rough guide to thinning (for me) is when it's like milk (marginally thicker than water) it's good to go. I suspect incorrect thinners weren't helping your apparent spraygun hassles - try again with the right type, and see what eventuates.

Cheers, Adam.

[durwood]

Don't waste your money buying a thermometer. If you add the correct thinner to the lacquer at the proper proportion it will be able to be sprayed in normal conditions. Temperature in the mid 20's. The temperature drops because the thinner draws heat out of the air next to it but if there is heat in the air as there is when its 20 plus it there is no problem. If its too cold you need to supply heat to the air to help the lacquer dry out quickly.

If the temperature gets over 30C or below 15C or its real humid you may need to add retarder thinner to keep the lacquer from palying up. Thats another problem but forget about it unless you have to spray when it cold or humid or raining.

The correct thinner for Nitrocellulose lacquer is Nitrocellulose lacquer. Acrylic Lacquer has its own thinner which is far too strong for NC lacquer. You get no advantage using it just like metho its likely to give you inferior results than you would normally get, it will slow down the drying time if nothing else. Acrylic lacquer thinner takes a month or more to completely leave the acrylic lacquer.

If you use acrylic lacquer as well as NC you can get a "general purpose" thinner which is meant to be used in both lacquers but its a compromise so both finishes don't reach the potentual they can. A spray painter will always keep both thinners and use the correct one.

If the lacquer is too thick the gun will have trouble drawing it out of the pot so you have to bump up the air pressure and when it finally does manage to suck it up it can't do it properly and the gun coughs and splutters. If you have a regulator the needle should be at about the 10 o'clock position which is about 60PSI do not go over that pressure, no normal gun needs more than that they are made to only run at 50-60PSI or you loose too much paint in overspray. Also make sure the hole in the lid of the pot is not blocked that will cause the gun to cough. There is a possibility you have a spray gun not made to spray lacquer and this will make it difficult to get top results.

Lacquers dry by evaporation which means they rely on all the thinner being released from the lacquer leaving only the dry resin coating. Most of the thinner is used getting the paint from the gun to the job. If you hold the gun too far away it dries out completely annd doesn't even get there.
If you put on a nice wet coat (which you are supposed to do) it should flow out, set up and begin to dry. It will be touch dry in a few seconds but it is far from dry enough. If you go over it too quickly the solvent coming off the first coat will be trapped under the next coat you put on and it will now take even longer for it to get to the air.

If you push too hard ( spray on too much too soon) you will mess the finish big time causing what is termed solvent boil. The underneath coats have so much solvent in them that when the top coat drys out (its the closest to the air) the others have to break through the dry top coat and you get tiny pin holes in the surface. Thats why you must wait between each coat. It doesn't matter how long but it does matter how short a time between coats. As you have to wait a few hours after the final coat there is no point saving a few minutes when you apply the paint. If you think about it one coat left to dry completely followed by all other coats each left to dry completely will give a hard dried right through finish not one which is still soft underneath.

Another thing to watch is that each coat is OK before you spray the next, if there is something wrong ( a lump of fluff etc) remove it before proceeding or you will trap the fault in the finish for all to see forever.

Addo, thinners doesn't go off, you can keep it for years in a container sealed to stop evaporation, same goes for the NC and Acrylic paint.

The correct viscosity for spraying paint is usually 20 seconds in a Ford 4 cup. 60-40 give you very close to that without the actual use of a viscosity cup.

[munruben]

I tend to use fresh Dulon "AAA Normal" thinners for most acrylic and nitro finishes. Metho in lacquer is a disaster waiting to happen and any thinners need to be newish; stored in a sealed container.

Absolutely. Thanks for that Adam. I can see no reason whatsoever for using meths as a thinner for lacquer. I should have mentioned that in my earlier post.

[addo]

I should clarify a couple of things.

Talking about thinners going off, was referring to the hygroscopic tendency of the products.

As to the thermometer - I suggested that because I'm self taught, and sometimes conveying fifteen years of experience in words is a bit difficult - so I looked at it as a practical way of "benchmarking" the right times to recoat. Plus... How many blokes pass up the chance to acquire another piece of kit?

You don't get inferior results comparable to meths when using Dulon thinners. Yes, it is slower to go off, but I find a good level of gloss "off the gun" to be consolation. I specified a particular brand as I too have observed some (other) acrylic thinners as being more aggressive.

Cheers, Adam.

[garfield]

so the spray your coat and wait ten minutes, then spray your next is out of the Question then

I have been spraying this lot just out in the open in my back yard... so I guess its getting direct sunlight - is that a no, no? I think todays temp in western Sydney was around the 22 - 24 deg mark

I really appreciate all advice guys and gals, so I'd like a big thank you to everyone who helps me out with all my threads. I'm marked down as a senior member because of how long I've been a member i guess but i haven't helped anyone out with a problem yet - but i certainly have been helped by so many with mine.....

as for this thread I think so far one thing is for certain, i shouldn't be using metho as a thinner

[durwood]

Garfield, It's Ok to use the lacquer in the sun light in the back yard ( as long as its not stinking hot, same as using a heater in a workshop to warm air) if you are spraying timber. If it was metal the sun would heat it up and you would tend to get the same effect as if you spat on a hot plate.

Aldo,
You don't get inferior results compared to metho you get inferior results compared to NC thinner. If you check out the compositioon of the two thinners you will see there is very little similarity between the two. They both contain some of the same solvents (so they will reduce them - even have metho in them) but some solvents are completely different in both formulas. If one thinners was suitable for both materials the paint companies would only make one. They actually produce several for each material and even change the formular for summer and winter.

If you use NC thinner the NC lacquer it will be dry and in 24 hours. If you use acrylic lacquer in similar circumstances it will be as dry in 14 days. The reason NC lacquer is still used is because it dries so fast, Acrylic has never been a favourite for use on timber because of its poor hardening.

Water is only a problem if you don't keep the thinners tin closed when not in use. Any problem from moisture comes from the air. From the compressed air if its not filtered properly and from the atmospheric air when the thinner evaporated and releases it onto the lacquer (blushing). We order thinners in 200 lt drums and it is often left for months often with no lids on the tins (students!!!) moisture isn't attracted to the thinner.

[Greg Q]

To add to the many reasons why metho is a poor choice for thinners is the fact that any easily available metho is going to be 5% water...kinda defeats the purpose of spraying in the first place.

[garfield]

Well I picked up my thinners last night from Bunnies and I'm gonna give it a go this arvo...... It is raining here in Sydney though