Viscosity when spraying

[mej]

Hi all

I purchased a 40L TradeAir compressor and Trade Air Touch Up Spray Gun from Bunnings. I am getting used to using the spray gun but just having a little trouble with the correct thinning procedure.

Gun has 1.5mm dia nozzle - set at 3 bar pressure - 1/4 inch air inlet and compressor is regulated with inline moisture trap. Paint is Dulux Aquanamel - water based - acrylic enamal - Gloss. MDF picture frame has been primed with White Knight MDF primer thinned 50 - 50 with water.

The Dulux Aquanamel just mentions if it is hot you can thin 1 litre of paint with 50ml of "Dulux hot weather thinners". I have been thinning using water at about 85ml of paint and 40ml of water. Although it sprays really well it is drying before hitting the surface. This is giving a sandy finish rather than a nice glossy finish. Any reduced thinning makes the paint too thick to spray (nothing comes out or it flutters badly)

If I use the Dulux hot weather thinners at say about 10% (90ml paint 10ml thinners) I think it is going to be still too thick for my gun to spray.

Was using water as thinner for the Aquanamel a big mistake, should I be using the Dulux hot weather thinner and do you think 90ml paint and 10ml thinner will be too thick for my gun to handle. I did read a thread that really warned against thining enamels too much.

Thanks for any advice.

Michael

[glenn k]

Don't know much about spraying but I was spaying fast drying enamel (not water based) and if I sprayed from too far away it dried in the air so I had to stay very close to job. ALso had to get wife to spay thinnners through the gun while I refilled otherwise it set in nosel.

[gumred]

Hi Michael!
You could try putting more product thought the gun , by turning the product screw , or putting a bigger tip in your gun, But a bigger tip , will also need more air, and your compressor may not be big enough
cheers, kevin

[mej]

Thanks guys. Well I checked with Dulux and they said it is cool to use water to thin but they stated firmly do not exceed 10% by volume of thinning. So I got a syringe from the chemist and measured out 90ml of paint and 10ml of water. I was suprised it sprayed at all but it did but it 'fluttered' somewhat. Approx every 5cm i would get no paint spraying out.I have the flow on the gun turned up to about 80% so the needle (1.5mm) on the gun is well open. I have the regulator set at 3 bars. I can go to 4 bars but that blows too hard. I suppose I could turn it up to 4 bars and bring the gun back a bit. The finish was better but there are still some "sandy" parts and you wont believe it I got some "orange peel" dimples going on. Fairdinkum!!! lol. I presume I have got some oil contamination from somewhere. Hoping that will sand back okay. I am just wondering wether the gun is sucking air from somewhere to give the fluttering problem. I think the problem is the gun to be honest.

Thanks for the advice guys I really appreciate it I will keep at it. I will not be detered.

Kind Regards
Michael

[durwood]

you haven't said what type of gun you are using. if you are using a suction gun (one with the pot underneath and a hole in the lid) you need to put in a lot more paint in the pot or the feed tube will not be immersed in the paint enough and the paint will suck air as well, especially as you move and slosh the paint around.

If the gun is a gravity feed (pot on top) then the packing gland at the back of the needle may be loose (can also be with the suction feed) . tighten if up until it stops the needle returning under spring pressure and then loosen it off a fraction till it returns by itself. It helps to have lubriucation at this point to help seal and make ithe needle slide easier.

If you are getting oil in the paint did you wash the new gun in solvent before use? there is usually oil put into the components when manufactured and it should be flushed out before use.

The gun probably is the problem, if you have any instruction sheet with the gun what type of paint does it say the gun is made to spray? Every paint requires different set ups ( nozzle needle air cap) I would suspect that a 1.5 nozzle is for enamel paint not for water based paint which as a paint doesn't like to be sprayed. Water as the thinner does not evaporate off as the paint is sprayed as happens with others thinners it lands on the job with the paint hence the advice not to put in too much, other thinners evaporate with the air and the paint arrives far thicker in viscosity flows out and sets up in a few seconds water stays wet for ages and the paint runs.

As you are getting dry spray its arriving far too dry so try adding a bit more water ( just a bit at a time) you may need to put in 15 -20 % to get your gun to apply a reasonably staisfactory satisfactory coating. Iv'e had to put in up to 50% at imes depending on gun, temperature and air supply. The paint company only can give you basic instructions they have no control over what equipment or technique you are using. The pressure is around the mark for most guns unless it is an HVLP gun. Only change it slighly up or down if you think it is helping to do so.

[mej]

Thanks for your comments.

The gun is an Air Trade brand from Bunnings and is a suction feed gun and is sold as a 'Touch up Spray Gun". I bought the "Touch Up Gun" because I only do small frames and thought it would be more suitable. It says - Automotive - Refinishing white goods - Hobby, art and craft - on the box. Definately a SUCTION feed gun with the pot at the bottom. I fill the pot about 75% full as per instructions. I thought too full would risk blocking the breath hole on top of pot.

Good point I was back at Bunnings looking at the gun with the salesman and noticed there was a lot of oil on the gun but I have used and washed my gun about 8 times. Not sure where the oil came from. I thought it may be coming from the compressor but after cleaning the gun I sprayed a glass for a while to make sure oil wasn't coming from the compressor.

The gun doesn't mention the type of paints it will or will not spray. I am going into Bunnings on Tuesday and we are going to call Trade Air with some questions. That will be one of them. Dulux does say the paint can be sprayed. If the solvent (water) isn't drying then the paint must be spitting onto the substrate to give that 'Sandy' finish. Which probably means I am not getting a fine homogenous mist from the gun, rather globules of paint spitting out. Too thick would be the answer there and the sucking of air would also indictate the mixture is too thick for the gun and every so often has to suck some air to get the paint up. I am pretty confident I have all the key areas tightened to prevent air being sucked in easily.

I may have to go from 9:1 mix to 8.5:1.5 mix and maybe even 8:2 paint to solvent mix.

One thing I do know is thinning the paint does eliminate 'fluttering' .

Okay off I go and try a new ratio mix.

Thanks durwood

Kind Regards
Michael

[KorDes]

I'd recommend exchanging it for a gravity feed gun (personal preference) with a tip larger than 1.5. I've found my 2mm tip works alot better with water based paints and 1.4/1.5mm tips work great with solvent based finishes.

[mej]

Hello

Well I am getting really close to a final finish. I diluted to about 20% with water and found by slowing down on gun speed I got a wetter coat of paint on. I thought it had dried 'sandy' but on closer inspection it was the very fine fibres of the MDF board coming through. A second coat of paint came up much more shiny. I have to really concentrate on technique cause if I am 'fanning' the coat doesn't go down even. I am straining the paint into the pot to eliminate specs appearing. I must be getting close because these are all major points people mention when spraying.

If I move up to a 2mm nozzle I will not have to dilute so much and get a thicker coat of paint on and less likely to get runs. I am just wondering wether the paint will go through my fine strainner though. Only one way to find out.

I think the 'oil dimples' was contamination of soap I had near the sink. I use the soap to wash my brushes so I have taken the soap away from that area. I wont do that again.

Okay once I get a final coat that I am happy with what is this ubeat wax and steel wool all about? Sounds like this product takes off small dust specs and leaves a clear protective coating once 'set'.

I hope it turns out I inserted a pic at the botton. This frame is still grainy but when the next top coat goes on it will really start coming up shiny.

Thanks for the help. All the great suggestions are helping me.

Kind Regards
Michael

[Bob38S]

G'day Michael,

Just to throw another element into the mix, as a thinning agent but one that doesn't change the consistency of the paint - claimed to be a paint extender - a product called "Flotrol" from the Flood company [Australian].

I recently had a lattice box which I had built to go around the HWS which needed a coat of paint, the brush lasted about 10 minutes before I used a spray-gun. The paint was thinned with Flotrol not water, just followed the instructions and it worked fine.

Regards,
Bob

[Honorary Bloke]

In my (admittedly limited) experience, a 1.5 mm tip is too small for paint. Try a larger tip and see how you go.

[durwood]

The size of the tip is only part of the solution.

Every spray gun can be different, the manufacturer makes the guns for particular applications. you buy the gun for the material you intend to put through it not because of the tip size. Quoted sizes are given by members of the forum here because most stores where these guns are sold only keep the basic ones so its big or small more often than correct one.

Most guns available off the shelf are aimed for general use, or for what the seller thinks most people will want the gun for.

A professional painter would ask for a gun to apply the paint he uses and he would have several different ones. Last palce he would purchase a gun from would be the local store , he would buy through a trade supplier or from a company distributing the gun so he can get exactly the right one.

Most cars now are refinished in a two pack urethane and guns best suited for this paint have 1.5 tips in them, what they also have is an air cap that is drilled to allow the correct amount of air to mix with the paint coming out of the gun so that the painter gets the full wet coat of material atomised properly.

If too much or too little air comes out the paint is too dry or not broken up and its lumpy.

If you used a gun made to spray 2 pack and tried to spray lacquer through it, it would come out a dry sandy mess. Use a lacquer gun for 2 pack and you would get runs and sags. No changing of the viscosity, air rate or paint amount would make it work as well as the right gun.

Our local training college has at least 7 different guns of the same brand each one for a different material - primer, lacquer, 2 pack urethane, air dry enamel, spray filler, lacquer putty, fibre glass resin as well as specialist guns for flock,
underbody proofcote.Then there is airbrushes and then some guns are gravity, suction low pressure or high pressure as well. Its a bit hard to get an learner to spray properly if the gun he is using is not the right one.

Go into a shop and you may get any one of the guns if it was put on the shelf along with others. Pick the wrong gun for your purpose and you have a problem.

It may seem strange but all paints are thinned to about the same viscosity if you follow the manufacturers instructions. Seems like they arn't but some paints need 150% thinner others only 10% to reach the same viscosity. They dry differently so the 150% thinned paint has a large tip to get a lot out of the gun for the air to attempt to dry on the way to the job. It arrives with most of the thinner evaporated and the paint is now thick and flows out and dries fast on the job.

The 10% drys slowly so less less air is used to mix with it only a small amount of drying takes place and again the paint arrives thick enough to then flow out and start to dry.

The painter has the ability to alter the thinning ratio and the amount of air and paint applied to the job. what he is attempting to do is get each type of paint to flow out and become a flat fault free surface. He can do that if the gun he has has the correct "Set Up" ( the term used to describe the air cap, fluid tip and needle)

Also when you buy a gun you have the choise of capacity of the gun ( how much air it uses). If your compressor is small there is no point getting a gun which has such large holes in the tip that it drains all the air out of the tank in seconds. So you buy a gun -(can be the same body size.) but with smaller hoes in the tip. you will not be able to spray as large an area in a minute but you can spray continuously. Its just the same as buying a 1" or a 4" brush.

So when you need to buy a gun check in the box for a chart, (should be one if the gun is a resonable brand) and check the capacity for you compressor and then the ":set up" for the paint you intend to put through it.

You could buy a general purpose gun it will be in the middle of the range of tip sizes etc you need but it can only do a "so so" job on all the different products you attempt to put through it and if you decide to try something way out in left field it won't work at all.

[jaywit]

Been in the game for 50 years,never out fo the trade except for 2 years national service.
As for guns,good ones cost but last,cheap spray but don't drop one!
Don't make things hard and expensive.Had about 10 guns (all DeVilbis) to use but kept to about 4.Pressure pot ,shading,Lacquer,any gun will spray anything,if it's too thick thin it or turn the pressure up,if it's dry open it up,if it runs close it down or move faster.If you can pee you can spray.
French Polishing the motto is little but often,look after the edges the middle will look after itself.
Spraying,work away from you and keep a wet edge,put just enough on before it runs.If you get overspray blow over neat thinners or very thin lacquer.
Mostly trial and error even the best screw up sometimes but" experience "is knowing how to put it right and knowing to expect the unexpected.
jaywit

[antcha]

10 years on and this information is just as relevant now as it was then.