Installing wooden laminate flooring on uneven existing floors is a bit of a challenge, but it can definitely be done. As long as the unevenness in your floor falls within your manufacturer's specifications, they are a few different options you can pursue to help make sure that your laminate floor installation lasts a long time and goes in without a hitch.
Check the manufacturers specifications for how level the floor needs to be. A general requirement is that floors be level within 6 mm (1/4 inch) over a 3 m (10 foot) span. If your floor falls outside of these requirements, you will have to have the floor levelled by a professional.
Fill in any low spots with a self levelling compound. This is only applicable to concrete subfloors. This compound is poured on the ground, where it automatically sinks into the low spots and then hardens, creating a level area.
Sand down any humps or high spots. Rent a floor sander to take care of wooden subfloors. On concrete, rent what is known as a concrete polisher. This will help eliminate any high spots.
Fill in trouble spots with roof shingles or shims. This is most applicable to a wooden subfloor where you might have valleys that can't be covered by levelling compound.
Allow the laminate to sit in the room where it will be installed for at least 48 hours. This allows it to come to room temperature and prevents them from swelling or shrinking with moisture after installation.
Roll out the plastic moisture barrier. Cut to fit the size of your room. Where two pieces come together, be sure to overlap them by at least eight inches. Attach together with tape. On wooden subfloors, this is not needed.
Roll out your padding. Cut to fit the size of the room. However, unlike the moisture barrier, do not overlap pieces and do not tape them together.
Start in one corner of the room. Take your first laminate board and set it in the corner. Use laminate or tile spacers to give this (and subsequent) boards next to the wall a 6 mm (1/4 inch) expansion gap.
Take the next board and saw it in half. Turn it so that the cut end faces the wall. You will be locking this into the first board lengthwise. By cutting it in half, you stagger the boards to give your floor a more natural look. Hold this board at a 45-degree angle to the first one and slide the tongue into the groove on the first board. Slowly lower the second board to the floor until you hear the board snap into place. Use the rubber mallet to give the edge of the board a few taps to ensure a good fit.
Take your third board and return to the first row adjacent to the wall. Install this board as you did the second board using the tongue and groove. Don't forget the spacers along the wall.
Repeat this process, alternating one row with the other, until you reach the opposite wall. For the last two boards in the rows, you will have to measure and then cut them to fit. Be sure to leave enough space for the expansion gap when you are measuring. Because the fit is so tight, you will have to wedge these two boards in place with the pry bar.
Start your next two rows, alternating the boards back and forth, and tapping with the mallet.
Measure the sides of the room for the installation of the quarter round moulding. This serves to hold down the floor and covers the expansion gap. Cut your moulding to fit. Remove the spacers on one side of the room. Nail the moulding into place. Repeat this process for the other walls.
The above steps are just a guideline. Always follow manufacturers instructions.
Use the proper safety equipment when using power tools.