Time. Space. Skill. This is what you need to work with HDU for signmaking.
I have a small shop with one table, and what I needed for a project like this is a dedicated work space. My HDU job was repeatedly on and off the table so I could get other jobs out the door. Huge PITA. The sanding process was tedious and took massive amounts of time, mostly done by hand because these were cut out letters and logo pieces. Tried using a rotary tool sander and an oscillating tool, found them too destructive to the foam. The dust is like baby powder and gets everywhere.
I painted everything by hand, another time suck. Sand, prime, sand again, paint 2-3 coats. Initially I thought I'd be able to knock out all the prep and painting in one weekend. LOL, try three, plus many late nights after hours. I used the FSC-88 primer as recommended for use with HDU, it was expensive and in hindsight, not needed. This went on like thick toothpaste, as someone else mentioned, even after cutting it with water, and ended up being a terrible foundation for the rest of the process. Lots of bleeding edges on the letter faces that required time consuming touching up, luckily I have a steady hand. Having the space and skill to use a paint sprayer is probably a better option, especially if the sign will be seen up close. Fortunately mine were installed 12-15 ft up where flaws and defects aren't as noticeable, but I was not proud of my work and that sucks.
My CNC vendor wasn't experienced working with HDU. Some instructions were overlooked in cutting and material was wasted. HDU is expensive, so another lesson learned there. He charged me for time he spent researching and watching videos on HDU. I paid him, but it bugged me. What I should have done instead of jumping into a big production job is order a smaller piece of HDU (eBay or wherever) and practice with it first. I actually did ask my supplier beforehand if they had any scrap or drop pieces and they didn't, so I bit the bullet and ordered two 8x4 sheets. Figured I would just "learn on the job", which was a mistake.
Halfway through the project, when I was losing steam and hope, I priced all the pieces in flat cut acrylic from Gemini thinking that maybe I should just start over. It would have cost me around $2,000 with freight, and I was concerned about the additional weight of acrylic as opposed to HDU for a wall installation. In hindsight, this probably would have been the way to go for time's sake, and to design the sign with consideration of potential freight costs if outsourcing components. Lots of hindsight lessons going on here.
In my small shop I share a kitchen/bathroom with the tenant next door. Naturally just as I started work on my project he had one of his own that took over the kitchen for two solid weeks. Between the two of us it was a disaster zone, and this was when I started drinking heavily. On the weekends I took the project outside under a carport, which of course invited everyone and their brother to check out what I was working on. I don't like being watched while I work, and I sure don't like strangers seeing projects in the making, especially when it's obvious who the client is. Lesson: have a dedicated space ready with everything you need for the project. I must have made a dozen or so runs to hardware stores for this & that...sanding supplies, paint supplies, Bondo, adhesives, hardware, Dremel bits, carving tools, etc.
Everything just took longer due to inexperience, and I lost big time on this job after factoring in all the time actually spent and miscellaneous costs. Will I ever make another HDU sign? Probably not.
