First let's take note as to why this happened.
Reason -1- under-mixed - Mixing is a crucial part of the project. Mixing of the product should be done by hand with a clean stir stick. The more product you are mixing, the longer it will take to achieve a complete mixture. One gallon of the mixture takes approx. 4-5 minutes of mixing. Two gallons of mixture take approx. 6-7 minutes of mixing. Timing this with a watch is a good idea. While mixing make sure to scrape the sides and the bottom of the container to avoid under cured epoxy. Be sure to push thoroughly down with the stir stick or, you can end up with areas that are hard/dry with other areas that are sticky or tacky that will not harden.
Reason -2- inaccurately measured - If you have measured and mixed your resin correctly, this problem will not occur. You must follow the strict 1 to 1 ratio by volume. Do not guess or eyeball these measurements. Just dumping the product from their original containers is not a proper measurement. It must be measured with reasonably precise accuracy using a graduated tub.
Don't worry - you can fix this!
Epoxy that remains sticky after the curing time will stay sticky unless the following measures are taken to repair the situation.
1. Scrape off the wet Epoxy
You will have to start by scraping off all of the wet epoxy.
Don’t worry - your project or art underneath will not be disturbed. Be sure all the liquid epoxy is removed before you pour your coat of fresh Epoxy on top. If you do not scrape off the wet epoxy, this could result in leaking under the new Epoxy coat. Wipe with denatured alcohol.
2. Sand your project (finish it off with 222-230 fine sand grit paper)
You'll want to sand the entire piece, next. Be sure to include the cured patch, if you needed to patch any holes or gaps. After sanding, wipe off any dust from the entire surface. (wipe it off with denatured alcohol or acetone)
The object is to create a layer that the new Epoxy can adhere properly too.
Don’t be worried if it looks like a mess at this point - when you pour the second coat, it will look as good as new!
3. Pour The Second Coat (pour 1/8"new flood coat)
Be sure that your first coat is 100% cured, and go ahead and pour your second layer.