This is not the way everyone makes their crochet synthetic dreads. This is my version of my own style. I am happy to share this as I believe everyone's dread creations come out differently despite using similar techniques.
Just remember to take your time and practise makes perfect :)
1. Take your back combed dread and crochet hook.
Small crochet hooks are best, I usually use a 055.mm - 1mm hook.
2. Put your crochet hook into the dread and snag a small section of hair.
3. Keep that first loop on your hook and move around the dread and snag another small section of hair. So you now have 2 loops on the hook.
4. Pull the first loop of hair through the second, leaving you again with one loop of hair on the hook.
5. Repeat this process down the dread. There is no need to be neat, just snag parts randomly on the side of the dread.
6. When you reach the end of the dread pull the final loop loose.
7. Repeat this process on the other 'side' of the dread, pulling in all the puffy parts of the hair.
8. Seal your dreads by pouring boiling water over them and leaving them to dry (outside is best). I usually repeat this step 2 or 3 times. You can use steam if you prefer.
If you have any questions please feel free to ask :)