I've just laid down the backerboard on a bed of mortar on top of the wood subfloor for a bathroom tileing project. I put in the backerboard screws, but could not get them flush with the board surface (slight raised heads). Home Depot told me that my subfloor is probably partical board and that the screws will not go into that material. I was told I would have to tear it all out and start over with plywood. Please tell me there is another way to have a smooth, flat prep surface for my tiles. Can I pull the screws up and just rely on the mortar adhesive? Or can I mortar over the screw heads, let dry, and then mortar for the tile? Help me please. Thanks.

What kind of screw did you use? There is a special screw for backerboard that has a burr underneath the head of the screw that counter sinks the screw hole as the screw is tightened. Otherwise you will have to counter sink each screw hole before driving each screw.

I used SuperiorBilt Backerboard screws.

Right screws, how long? Should be long enough to penetrate the wood sufficiently to pull the screw head below the surface. Don't let the screw spin out (enlarge the screw hole so that it has no gripping power). You could remove the existing screws, counter sink the holes and install longer deck screws. If you do indeed have particle board subflooring you will have to be very careful to not strip out the holes. I doubt that you have particle board subflooring.

You know sometimes the folks at HD are just plain wrong. 1/2" backer uses a 1 5/8 " screw while the 1/4 " board ises a 1 1/4" screw and they both will dig into a particle board sub floor. Why did the screws not set flush, did your drill just bog down or what?

Thanks a bunch there Art, I see you been doing quite a bit of reading here tonight, enjoy!

What they told you is a bunch of crap.

1. When you install your BackerBoard, I would first suggest that you predrill the screw holes with the appropriate size cement drill, another words, drill the hole the same size as the screw, this allows for the screwto pass easily through the BackerBoard, it's the underlayment that draws the BackerBoard down tight against the underlayment. Be sure that when you predrill the holes in the Backerboard that you don't drill into the underlayment. You can purchase drill bit collars from Home Depot or Lowe's that will allow you set the correct depth... onto the next step.

2 Now that you have predrilled the BackerBoard holes, use a second larger cement drill 3/8" to countersink the holes, in this way, the screw will always be below the surface.

3. Use brandname 1-1/4" square head BackerBoard screws, they drive better with less swearing due to stripped Phillips heads. I would also recommend name brand 1/4" BackerBoard, not plain cement board, pay the few extra pennies, it makes for a cleaner installtion. Make sure that that your floor is properly supported with a plywood underlayment, if there's any sponginess, this will also cause cracking of floor tiles..

If you fail to install the screws properly, the heads will extending above the surface, when you walk on the tiles, your going to start seeing cracked tiles, maybe not right-a-way, but cracks will start appearing after the tiles have been subjected to downward pressure from your body weight.

Does this require extra work to install the BackerBoard in this fashion, YES, but I can tell you that from 47 years of experience in the business that this is the only way to "DO IT RIGHT." In 47 years I've never had a cracked tile complaint, other than dumb stuff like carelessly dropping a heavy cast iron frying pan on the floor.

Preparation is 199.9% of getting it right the first time.

Tileman