resin infusion and pigments

use of white pigments in resin infusion process wanting to avoid coating the mold with a gel coat prior to infusion

 

Gelcoat is not the same as laminating resin. If you put the load and pigments that gelcoat has it will have difficulty wetting the fiberglass. Tinted resin is usually used to prevent translucence.

 

....emmm, you obviously do not understand the infusion process, it is one of the best ways to get a true wetout and minimum resin content, without the faults of gelcoat/laminate layups.

Gelcoat is porous...it is not a good thing to do to a frp boat, but it is done to not show the obvious faults that occur during laminations!!!!!!!

Gelcoat is not allowed on survey boats for that very reason.

The underwater sections of a poly resin or even vinyl ester resin laminate MUST be epoxy coated to give the hull some chance of waterproofing if you expect the vessel to remain trouble free.

 

When you go all the length to infusion, why not Epoxy?

 

.....indeed....if you go to all that trouble, cost of epoxy over poly is bugger all...you do not use all that much resin anyhow really.

 

There are many reasons to want to add pigment to an infusion resin, but the results are typically not good enough for most applications.

In infusion the glass acts as a very fine filter, so depending on the type of pigment and how much is added, it can be filtered out in some areas and look uneven, or even block the flow.

Plus the surface will never look like a gel coated surface, it will be a bit dull, slightly translucent (due to low pigment loading) and you still have fibers right at the surface which will be visible from the print through at first, then even become even more visible quickly from weathering.

The lower pigment content will also result in very poor weathering compared to a gel coated surface. Gel coats rely almost 100% on pigments and fillers for UV protection and the base resin is chosen for good performance in this application also. Laminating and infusion resins aren't normally designed or formulated for good cosmetics when exposed to UV, so they will typically degrade quicker. Then add in the fact that the pigment load will be much lower than in gel coat and you end up with a surface that doesn't look all that good to start with, then deteriorates relatively quickly from there.

There are many applications where the finished product is "good enough" though, industrial parts, the inside of areas that are rarely seen, its even used to hide trim edges on gel coated parts by giving the entire thickness of the laminate a similar look and color, this can reduce or eliminate the need for coming back and coating the edge later in the production process.

 

Ondarvr deserves positive feedback for his reply.

I would like to add that it is perfectly possible to use pigments and even fillers (up to 50%) in resin infusion. Do not expect a gloss finish, but ondarvr already said that.
It all depends on the particle size of the pigment and filler, and the permeability of the infusion stack. You need high permeability to prevent filtering of the pigment. This will also cause a low fiber to resin ratio. Something boatbuilders usually try to avoid. However, in industrial products it is nothing new.

There are also soluble pigments, which are no problem to infuse, even in high fiber/resin ratio laminates. They are not opaque, however.