I'm using Marinepoxy with a slow hardener. What is the maximum "green" time for the epoxy during which I can put on a second coat without sanding. Assume daytime temperature of 80 with nighttime temps of 65 degrees. In reality I always sand a bit, so the surface dulls a bit and I can see where I've applied the second coat and not miss any spots.
Dave
Also, when one does need to sand between coats of epoxy, with what do you clean the dust? I've heard never to use Acetone and never to use denatured alchohol. But from others, I've heard both are ok. Would appreciate help with this as well as the "green epoxy" question.
David: Don't worry about removing epoxy sanding dust before the next coat of goo. Just brush it off with a shop brush and put the next coat down. Any residual dust gets incorporated into the epoxy coat, and is invisible. Almost like fiberglass cloth in dust form!
Dave
I used an ammonia solution. Get the Gugeon Brothers epoxy manual. It's free on the West System site and is indispensable for this.
Amine blush is water soluble and a light scrub with a ScotchBrite pad and water is all you need. A little dish detergent soap can be helpful too. Do not use solvents on amine blush, you'll just smear the stuff around. The only exception to this solvent rule is, alkaline substances (like soap or ammonia).
The green time is dependent on many factors, but the thumbnail test is a good indication. If you can easily dent, the seemly dry to the touch epoxy, it's still green and will accept an over coat without sanding. The ass kicker is, you don't know when it's green and blush free or green and has a blush. So, the general rule is, if it's dry to the touch, you should lightly scuff it with a pad, even if you can dent it with a fingernail. The only time this isn't true is when you have ideal laminating conditions (no one does).
It's safe to over coat without sanding, if the epoxy is still tacky or has just lost it's tack within the last hour or so. Much later then this and amine blush is beginning to form, so you can't risk it, without good control over environmental conditions (air conditioned shop). The use of "peel ply" can to a large degree, help with blush. If you use a peel ply and can dent the goo with your fingernail, you're safe to over coat without sanding.
Sorry to chime in so late but health issues have been occupying much of my time lately. When I built I wanted to use several light coats and I didn't want to sand in between so I set a timer for 4 hours and recoated. It was still slightly tacky. My wife thought I was nuts getting up at midnight and again at 4am but I put on enough coats to push me to those limits. I also used marine epoxy with slow hardener and it was in the mid 70's to mid 80's in the shop at the time. I think I could have went to 6 hour intervals but opted for the 4 to get the work done.
There are ways to speed up the "gel" time of curing epoxy. If the surface has been previously coated, just apply heat. You can half the cure time, just be getting the area up to 85 - 90 degrees. A few heaters, spaced around the project, maybe with a tarp tent over the work to keep the heat in can take a 6 hour cure to 3 or less. This shouldn't be done on raw wood coats, as things will out gas, but any other coatings will be fine. If I'm in a real hurry, I cover the project with a black tarp and place in it full sunshine. The temperature inside gets into the 140 range which quickly cures goo.