JB-Weld is a lot cheaper or more simple than installing new rivets. I have one that has JB-Weld all over the bottom side. She's seen some rocky bottoms ponds in the past, so it's a little 'beat up'. The JB-Weld has stood up very well for me. There's also an epoxy that's designed for submerged use also, that I've heard works well.
I've been there, and done that, and did it again, and did one more time, and then did it again.
First, what Bassquatch said. For John Doe, (you and me) it's a waste of time to try and tighten or replace rivets.
Second, J-B Weld will do as good as anything and better than most.
Third, the other thing that works is the green-blue sticks you can get from various catalogs. They work like sealing wax.
Fourth, what will not work are the sticks that look sort of like solder. You will ruin your boat trying to use them, and they make a brittle repair that won't keep the rivet water tight. Please trust me on this (and my experience has been verified by others).
Fifth, I've read about people trying, but I've not tried, Herculiner, the DYI truck bed liner. A lot of people are coating the bottom of their boat with it to increase abrasion resistance.
Do not try fiberglass patches-- they won't stay on.
I used UV activated Bondo and it works great and very quick. Two weeks later I turned the boat over and it was still wet inside until the sun hit it. It was dry in 15 minutes. If you are in a hurry try this. Apply in the shade first and then expose it to the sun.
I dont' know about rivets but on my fiberglass one I got some water weld at wal-mart that has done really well. Looks like two tone putty, knead it and it will get warm, then put it where you need it and it sets up fast. It's worked great on mine so far.
To Do It Right , Use Herculiner Bed Liner. I Just Finished Doing My 14' Jon Boat. A Gallion Kit Includes Everthing You Need To Get Started. At Autozone It's $91.00 , This Is Enough To Do The Bottom A Couple Of Times And The Inside A Couple Of Times. Your Boat Will Never Leak Again. You Will Need To Get A Couple Of Cheep Brushes, Once You Put A Brush Down It Hardens So Fast You Can't Use It Again. This Stuff Is Wonderful, Spend The Money, You Want Regret It. Those Cheep Fixes Are Just That. Herculiner Seals, Makes Your Boat Quieter, And Slip Proff .
IF YOU HAVE ONE LOOSE RIVET IT'S JUST A MATTER OF TIME BEFORE YOU HAVE ANOTHER. IF YOU HIT THE SPOT THAT HAS BEEN FIXED WITH THOSE CHEAP FIXES THEY WILL POP OFF IN ONE PIECE LIKE OLD GUM UNDER YOUR CHAIR. IF YOU GO TO SELL YOUR BOAT AND YOU HAVE 2 OR 3 OR EVEN 4 WAD'S OF GUM LOOKING STUFF ON THE BOTTOM OF YOUR BOAT DO YOU THINK THAT PERSON IS GOING TO BUY A LEAKY BOAT, I KNOW I WOULD NOT BUY ONE. I HAVE USED THOSE CHEAP FIXES BEFORE, SO I KNOW WHAT I'M TALKING ABOUT. FIX IT RIGHT AND YOU AND THE NEXT PERSON WHO GETS THE BOAT WILL LOVE YOUR BOAT KNOWING IT HAS BEEN TAKEN CARE OF THE RIGHT WAY. JUST LIKE A USED CAR YOU LOOK AT IT AND IF ITS RODE HARD AND PUT AWAY WET IT SHOWS AND YOU KNOW TO PASS IT UP UNTIL YOU FIND THE RIGHT ONE. OH BY , THE WAY MY MATH DOES ADD UP, TO ADD YEARS TO YOUR INVESTMENT FIX IT RIGHT.
To fix it right you need to replace the bad rivet. If you have the proper tools it will only take about 5 minutes to do. That rivet not only holds the water out, it also holds the boat together. So one loose rivet fixed improperly with jb weld and Herculiner Bed Liner will lead to two loose rivets.
Md with you living down in Newan you should be able to find an aircraft mechanic pretty easy. Delta has quite a few down there.