i tried a new process on a gelcoat mold. i wanted an IMC to help with surface finish. I used Frekote FMS and release followed by Duratec -061. I was very careful with FMS and release. I sprayed the Duratec but immediately got what can be seen in the attached image. The spray never wanted to film. I used an HVLP gun with a dry air supply. I started the duratec with a film followed by a heavier layer. I am lost and have no idea what i did wrong.i also tried to resize image to no avail apparently
Standard issue with using an IMC over a high slip release agent like Frekote.
There’s a couple of things you can do to help. The first is apply 2-3 coats of a silicone free paste wax release agent over the top of the Frekote. Be gentle when applying and buffing the wax off so you don’t remove the Frekote. This will give you a bit more surface tension and help prevent the separation of your coating. Be aware that if you reuse the mould, you will have traces of the wax still on the surface so you don’t want to apply any Frekote over the top as this will cause contamination. For reusing the mould, just apply another coat of release wax and you’re good to go.
The second thing is your spray technique. For the first 2 coats, up the pressure at your gun to 50psi. Reduce the material flow nozzle so that you can barely see any material coming out of the gun. When you spray onto the surface, the material should cover it more like dust than a film, there should be no separation at all. Apply 2 coats in this manner with 2-5 minutes between them to allow the material to setup (2 minutes in warmer weather, 5 minutes in colder weather).
After the 2 dust coats, open the flow nozzle a touch more so that you can now easily see material exiting the tip, but still not full flow. Spray one coat like this, slightly heavier than your dust coats. The surface should now have a visible film on it. You may at this stage get a bit of separation occurring, don’t panic. Allow this coat to setup again for 2-5 minutes.
Now you should be ready to build your film thickness. Reduce the gun pressure to 35psi, and open the flow nozzle to how you would normally spray. You can now spray as you normally would and build to your desired film thickness. Allow each coat 2-5 minutes to flash off in between, and try to avoid going to heavy or you risk runs/solvent entrapment. Don’t panic if the film appears to be quite beaded still, after 3-4 good wet coats these beads should fill themselves in and level out.
It can take a bit of patience and a bit of practice. I recommend measuring a few batches of the costing and catalysing each separately to give you more working time, ie. Rather than one 500ml batch, mix one 50ml batch for your dust coats, then one 200ml batch and one 250ml batch. This will make it less stressful and reduce the temptation to rush through your coats before they have had enough time to setup. That really is the key, the coating needs to set up as a flat film before you add to it and it tries to form a sphere.