[Hocsoc779]

Started a bar top….seemed like good idea now not sure how to finish the top?!? How can I fill in the cracks before sealing….?

 

[GeorgeC]

I would start over again and get a much better fit of the wood pieces. Anything that you do to fill those large gaps is going to look bad.

George

 

[Tony B]

How are the top boards attached?

 

[Hocsoc779]

My brother glued them on…so starting over won’t be as easy at all

 

[Tony B]

This wont be cheap: Mix up epoxy, dye it black and pour it all over the top so it can run down the cracks and fill them in. Then when the epoxy sets, sand the whole top down to the wood. then pour clear epoxy over the whole thing.
OR
Rip it up and start all over again.
If it were mine, I would rip the whole thing out and start over.

 

[woodnthings]

If you can't or won't start over, you can fill the cracks with epoxy mixed with various other materials.
This site has fine crushed stone;

https://www.ehow.com/how_7375267_use-crushed-rock-filler-epoxy.html

Or colored dye or mica powder:

https://artincontext.org/coloring-epoxy-resin/

Your photo shows great unevenness on the blocks.
Take a 36 grit belt or disc sander and level out the top before adding any fillers.
This will save you money when you put the clear on top because it will take much lees to cover it all.
This site is the best for learning how to make epoxy top tables:

 

[michael48]

Maybe you could cover it with glass, tempered 1/4inch thick and put a nicer edge band on. Might be expensive though.

 

[_Ogre]

I suspect that this is a low dollar build. Epoxy is not going to be the cheap fix. Sand the top smooth polyurethane it and caulk the seams. It won't be waterproof, nor will it hold up well. It will be a cheap fix 🤷

 

[Tony B]

If you own a table saw or have access to one, re-saw all the boards to the same width so there wont be any gaps although you probably wont be able to remove them to be able to saw them. Unfortunately, you are stuck with what you got and so the easy way out would be as @_Ogre suggested above. If it were me, I would scrap the whole project and start over again.

 

[woodnthings]

You don't need to start over in my opinion. Fill in the large gaps with small pieces. Build up all the surrounding edges to form a "dam" to contain the epoxy about 1/8" over the highest block. make sure all the small seam are sealed with adhesive like Liquid Nails but do it neatly. The epoxy will find the smallest crack and flow out.
use a clear bar top pouring epoxy such as Blacktail Studios uses. I may require two applications, watch the video to learn the process.
The epoxy will be expensive but you will end up with a far superior finished result over poly.

 

[LilMtnDave]

You don't need to start over in my opinion. Fill in the large gaps with small pieces. Build up all the surrounding edges to form a "dam" to contain the epoxy about 1/8" over the highest block. make sure all the small seam are sealed with adhesive like Liquid Nails but do it neatly. The epoxy will find the smallest crack and flow out.
use a clear bar top pouring epoxy such as Blacktail Studios uses. I may require two applications, watch the video to learn the process.
The epoxy will be expensive but you will end up with a far superior finished result over poly.

I like the epoxy ideas. How would the vertical parts be done?

 

[Tony B]

Another idea:
Instead of replacing the boards which will be a royal pain in the rump, start layering a new layer on top. This time use a table saw and whatever else you have available to make parallel cuts on the boards so that they will lay against each other without gaps.

 

[woodnthings]

Another idea:
Instead of replacing the boards which will be a royal pain in the rump, start layering a new layer on top. This time use a table saw and whatever else you have available to make parallel cuts on the boards so that they will lay against each other without gaps.

That would mean losing all the rustic? detail, color and character of the existing boards. It would look like a section of flooring if all the boards were overlaid with new.
If the boards were the same , what's the advantage other than tightening up the gaps, another character feature. I'll let the OP decide, but I wouldn't do that.

 

[Rebelwork]

We use epoxy for tops like this at tge furniture company. Read and understand the directions..

You can always apply anot her finish over it..