sanding 2k- feels like grit

[imaginarynumber]

I am spraying mdf. The first coat was Morrells 2 pack white primer. Sanded back with Festool (Titan) 360g.

The next coat was a 30% sheen coloured finish. Unfortunately when I sand the first top coat (400g), dust off, tack cloth off and spray with the dusting gun, the finish still feels gritty.

I am spraying under non-ideal conditions, namely in a gazebo. Using HVLP (turbine). post sanding, I have tried to wash down with thinners and also water. The finish looks flat but running my hand over it after a second or two feels like someone has poured fine sand over it.

The last time that I experienced this was early in the year when the temperature was about 10 degrees.

I guess that the paint hasn't sufficiently cured. Will extra catalyst help or do i need to invest in UV lamps or something similar?

Any help will be appreciated. Tnx in advance

 

[mailee]

I am not sure about the turbine HVLP setup but I regularly use Morrells solvent 2 pack ac lacquer with a gravity fed HVLP gun. I mix it 9 parts to 1 and only thin enough to flow through the gun (if at all) Once I have given it two coats of primer and it has hardened I sand with 320 grit dry. Then I wipe it all with a tack cloth and blow it down with the airline. I then apply two full top coats of colour without sanding in between coats. Once it has cured if the finish is a little rough I would sand down with 1200 grit wet and polish to a finish. HTH. :wink:
P.S. I have just noticed you mention dusting gun? I am not sure what you mean by this remark?

 

[imaginarynumber]

hi mailee

Thanks for the reply.

By dusting gun I meant the type connected to a compressor

http://www.axminster.co.uk/air-dusting-guns-dept206847/

My work practice is not unlike yours but I do tend to sand the penultimate coat, in part to eliminate any contaminants that landed on the surface. As I said my set up is far from ideal on this job.

The grit that i referred to almost feels like dust that has refused to leave the surface (and clumped together). I can only assume that the temperature drop or air moisture has something to do with it.

After dusting off/tacking/blasting with compressed air (and sometimes even washing with solvent and or water) the surface feels smooth for a second or two and then gritty again.

Working in the same environment during warmer weather doesn't present this problem.

 

[heatherw]

It could be that you're not putting enough solvent in the mix and so it's drying before it gets to the wood. You could try putting more solvent in to see whether that solves the problem. Te mix usually has to be very runny, more than you'd think.

 

[mailee]

It certainly sounds like it is down to the temperature from what you have stated. I would suggest trying to heat the area up somehow. Is the paint water or solvent based? If it is water based then it will be far more susceptible to the temperature. Once dry is there a blush or dull bloom on the painted surface?