CLEAN and DRY
CUT and CUT AGAIN
PUSH AS YOU GO
GET SOMEONE TO CHECK YOUR BRICK
If your bottle is even a little damp, or your plastic has any moisture, stop! How will you feel if after all your hard work your bottle goes mouldy and can't be used?
One of the most common errors is to put the plastic in the brick without cutting it small enough. The smaller the pieces of plastic, the more likely you are to make a successful brick. Better to cut too small than to leave pieces so big that they have air pockets and then, yes, the brick isn't solid enough.
You need a pushing stick - most people start with a long-handled wooden spoon which is used to ram the plastic down inside the bottle. But another common error is to not fill the base of the bottle sufficiently well. If the bottom third of your brick is squishy but the rest is solid, you won't be able to reach the squishy plastic to squash it down, and then, surprise, your brick won't be solid enough.
It is heart-breaking when someone arrives at the community shop with a big bag full of ecobricks and none of them are good enough to be used. Once you have completed your first brick, ask for feedback from someone who knows what a good brick should feel like. We are happy to meet you at the shop and give advice (much better than telling you we can't accept the bricks you have spent months making).