Spray Gun Options
I’m reproducing a part in carbon fiber, which requires me to make a mold of the existing part. For accuracy and durability of the mold, it’s best if the first layer is sprayed gel coat. Gel coat is normally sprayed with a “cup gun” like the E.S. G100 Cup Gun. At around $175, it’s more than I’d like to spend for my relatively small project, though I’m sure it’s great for professional use.
Since I already have a couple of the purple Harbor Freight HVLP guns, I wondered if gel coat could be shot with an HVLP gun. My Harbor Freight guns have 1.3 and 1.4mm tips, which are great for shooting paint and primer, but gel coat is extremely thick compared to even a high-build primer. This spray gun website recommends a 2.0mm or larger tip for playing gel coat. It recommends 2.5-3.0mm for “full coverage on boats”, and claims to have guns up to 7.5mm for large molds!
Unfortunately, Harbor Freight doesn’t sell additional tip sizes. It may be possible to find out what gun Harbor Freight copied, go to a local auto body supplier, and look for replacement tips there, but that will almost certainly expensive. Most likely, it’s cheapest just to find a complete, Chinese-made HVLP gun with a tip in the 2.0 – 3.0mm range.
This boating forum discussion recommends the Vaper HVLP spray gun with 2.3mm tip for $39.99 at NorthernTool. Shipping is $7.49, and it’s currently backordered, so I kept looking for other options.
I then found this listing for a 2.5mm HVLP gun (eBay seller yescomusa) for $37.90, with free shipping. This appears to be the cheapest option, and it doesn’t require me to swap out any parts when I want to go from shooting paint to shooting gel coat.
Another option might be the texture spray gun from Harbor Freight, intended for shooting popcorn texture on ceilings. It’s $26.99, and comes with 4mm, 6mm, and 8mm tips. This forum post says it works well.
Gel Coat Options
TAP Plastics has white or neutral gel coat, without hardener, priced at one pint for $17.25 or one gallon for $89.50.
A cheaper option is eBay seller promboats, who sells a quart of white gel coat, with hardener, for $25.50 shipped.