It is a bad idea to come here and ask this question!
First, the answer is dependant on the exact chemisty that you are using. There are HUGE differences in one 100% solids product versus another one. Our company has almost 5000 formulations of products that are 100% solids! Obviously, you wouldn't have that many if they were all the same.
What you need to be doing is asking the manufacturer of the product you have purchased what they recommend.
Expansion joints will not fill in with any epoxy very well especially the thick solid type like you are using. (I also used 100% solids) What happens is you will get air trapped in the joint and when that bubble does come up, you will then get a imcomplete joint. Best thing to do is fill the joint with an appoved filler or second option which I did was to use silicone to fill the joint after you have painted.
If I did it all over again, I would properly fill the joints first. Good luck.
PS> the above problem really shows up when you have cracks too. Those must be filled first.
This is good advice:
1) Use an approved (by the manufacturer) Joint filler...
2) Fill the joint AFTER it is coated with flexible silicon (I wouldn't do it this way but it will work)
You can use cabosil (fumed silica) to thicken pre-mixed epoxy. Turns the honey into peanut butter. A drywall knife will work well to apply over rough areas or cracks.
I hope the poster won't take offence at my criticism of this idea. There ARE cases where this will work but it is NOT a good generic fix. First, whether this works or fails depends on the flexibility of the material that you are going to thicken. Second, there are a BUNCH of grades of Cabosil that vary based on surface area and linear structure. IF you have a product that would be flexible enough to do this with, you would use Cabosil M-5 or Aerosil 200 or 202 from Degussa (now Evonik). Typically, products that will work in this manner are flexible and soft. There are a handful of products that are flexible without being soft but there are only a few of us that make them. In general, this is a bad practice and the joint will fail by cracking prematurely and before the coating fails.
It's best to do this job once and do it right. Ask the manufacturer what they recommend before taking advice from a bunch of Joes (myself included) that don't even know what Brand or Product you are even using.
