Thread: Questions on epoxy coating technique.

The best thing you can do is download the free "User's Guide" from Epoxy by the Leading Epoxy Manufacturer | WEST SYSTEM Epoxy and the "Epoxy Book" from - System Three Resins, Inc..

These will nurse you through the basics an familiarize you with materials, techniques, etc.

Precoating can be desirable, though also wasteful as you coat off cut stock too. I precoat when I can.

Thanks for those links. Very useful. Read all of it.

Finally got the pre coating done. Had to wait a couple of weeks due to having no time or rain. Got to read a nice article about temp, humidity, relative humidity and dew points. Good info except it never gets dewy in the garage. Decided to play it safe and wait till the rains passed.

Panels all precut and the butt joined together. Got the three coats on over the space of about 7 hours.
Overall I am pretty happy with the result except I think I may have gone a bit thin on the coats, or my technique sux. I did the roll and tip.

The coating not 100% flat. Has a bit of a wood grain effect to it. The parts where I used more resin, around the butt joins are far smoother.

Anyway.... One of the panels will be getting painted clear so I want a really nice smooth finish.
Is it best to sand it flat and then clear coat.
Or sand it lightly to flatten it out a little and then add another coat of resin?

cheers!
mike

Whichever you do - clear coat or more resin - you will need to sand thoroughly.
If you cut all the way through the resin to bare timber in getting it flat, build it back up with more pox.
Otherwise, clear coat.
all the best with it
Alan

If you want it smooth, you'll need to knock down the stipple and brush strokes or grain lines. Grain lines usually need to be filled, with more goo, before you can knock it down. I usually wet sand with 180 - 220 first to remove the irregularities, then move up to 280 wet for the finial wet sanding. Sanding with the grain of course. You can get real anal about this part of the job, but usually it's best to just get it as smooth as practical on the epoxy, then stop and bulk up the finish coats, which will also need to be "blocked" down (wet) and smoothed. It's a three stage process - the first is to level the epoxy, next is to bulk up and level the clear coats and lastly is to bulk up and smooth the final coats of clear. The final coats of clear are more about application techniques, being clean and under the right temperatures, than sanding. Depending on the type of clear coat used, you can often buff it, which will smooth it out further.

Why wet? Is it ok to use a random motion orbital? And do it wet?

A DA or random orbit sander will leave "swirl" marks all over the place, which often (usually) show through clear wood finishes as miniature "thumb prints". Even if you use 220 or 280 grit, these marks will stand out like red dress at a funeral.

This isn't the case with painted surfaces, just clear finishes, where all final sanding must follow the grain, if you exspect to hide them or you're useing a ver specialy type of coating, that will permit much, much finer grit (over 400). Typical varnishes and polyurethanes will not tolerate too fine a grit and still provide enough"tooth" to hold subsequent coats of finish in place.

I wet sand for a few reasons, but mostly so I can see what I'm doing. When you dry sand, the coating quickly becomes cloudy and you can't really see what you're doing. If stipple is fairly heavy, you can see the dull and shinny spots easily, but if the surface is already fairly smooth you can't tell if you're over working or under working an area. If wet sanding and the light is coming from an acute angle, you can see reflections in the wetness. This is what I go by to insure things are actually smooth. This said, some do final sanding dry, particularly if they already know the surface is smooth and are just bulking up film thickness. This is fine, if it's what your use to. Simply put undulations are hartd (for me) to see if the coating is dry, so I sand wet, which is also cleaner, so the area doesn't need to have as much prep for the next coat.

Originally Posted by schmik

The coating not 100% flat. Has a bit of a wood grain effect to it. The parts where I used more resin, around the butt joins are far smoother.

Anyway.... One of the panels will be getting painted clear so I want a really nice smooth finish.
Is it best to sand it flat and then clear coat.
Or sand it lightly to flatten it out a little and then add another coat of resin?

cheers!
mike

One trick you can use for rough surfaces is a scraper instead of sanding, to get rid of the worst lumps first. I have one similar to this:

15313.04524_4.jpg

It works well if used with a little care. I put the weight on the blade with one hand and drag the handle with the other. You can do this without digging the corners in, and you can do it when the epoxy is still not 100% cured (ie: hard to the touch, but still stinky). It can make for much cleaner and easier work in the initial stages.

The only problem with a scraper, particularly that type is just one mistake and you're really sorry you used it. If you do use it, round over the two corners, so you're less likely to yourself off. I prefer cabinet scrapers, as you have more control. Lastly with scrapers, they have to be sharp, really sharp. A worn out edge can make a mess of a finish quickly. Learn how to sharpen them. It's not hard and it is fast, once you have good technique. I sharpen mine in less than 30 seconds.

All true. I should point out that I wasn't recommending using that sort of scraper on concave surfaces. Flat, or convex, is ok. Concave would be disastrous.

I use a dreadnought file to knock down the large lumps.
Reasonable control over flat & convex surfaces.
Can handle some concavity, but you need to flex the file, & work more carefully...

I think we all have techniques for various smoothing operations, though I tend to assume the most basic of skills, so shy away from specialized tools and methods, in favor of what most will probably feel comfortable with. A sanding block and a garden hose dribbling over the area is about as simple as it gets and no blade sharpening either.