Uneven plywood is the likely cause of cracked ceramic floor tiles
Q. The 12-by-12-inch ceramic tiles in my bath and kitchen were installed 14 months ago by a contractor. Now 10 to 12 tiles have cracked, right through the tile, not in the grout lines. It's in a straight line for the length of the room. The contractor won't answer my calls. What's wrong and how can I fix it? The floor underneath is plywood.
RAY MELLO, Stoneham
A. Ah, the fact that the tiles cracked (not the grout lines), and the straight line of cracks went across the room, are dead giveaways (I think) that the underlayment (the plywood or particleboard under) is at fault. What happened: When two pieces of plywood were butted together, they weren't even; one was a bit higher than the other; a difference of just 1/8 or even 1/16 inch can cause a problem. When the tiles were laid (with thin-set mortar or adhesive) each overlapped the joint by about half. Then, when the tiles were stepped on, they rocked, like a teeter-totter over the apex (the plywood joint), eventually causing the crack. At least that's what I think happened.
A drastic and expensive cure is to take up the tiles and plywood and relay new plywood even with each other. But here's a trick you can try: Take up the cracked tiles and sand those uneven pieces of plywood so that when the new tiles are laid they will not rock. Sometimes thin-set mortar will span the uneven edges of the plywood if it's applied thickly enough.
The contractor is avoiding you because he knows what happened.
Q. I have central air in my apartment. When I shut it off I can hear water dripping into a puddle. Can I wet-vac it , or call a specialist?
TIM, Hotton's chat room
A. Apparently, you have an air-conditioning unit in the apartment, and that dripping water is condensate dripping into a collection pan, from which it is then pumped outdoors. If you have no water leaking onto the floor or elsewhere, I say, forget it; the unit is working as it should, and the water you hear is being dripped into a collection pan and the unit pumps the water outdoors. If you see water on the floor or anywhere else , then call the specialist .
Q. Can a do-it-yourselfer safely replace a gas oven with a new one? It looks straight forward enough to get a new flex-hose and attach it to the gas line. But it's gas, so . . .
KENNY, Hotton's chat room
A. No, it's illegal for a layman to work with gas, and for good reason. You must hire a gas fitter.
The only other suggestion the handyman could make was to break into a wall to see if there was an old fire from which the odor can persist for a long time. The handyman also suggested that it might be a broken heat exhanger in the hot air furnace, in which case the odor would be of burned oil, and it's a hazard that must be addressed immediately. So, he tossed it out for anyone who might have a different idea.
Here is what one e-mailer wrote : " Another way to check if there was a fire is to call the fire department; they should have records. "
And, in an another e-mail, John Misuraca wrote: "I read your advice today to a condo owner with an intermittent fire smell. I see that they have a heat pump backup system and wanted to inform you and them of a problem I have seen from time to time. The air handler for the heat pump usually has an electric heater in it. These heaters could have dust buildup on them causing the smell. Someone may have even removed the filter. Sometime new condo owners don't even know there is a filter that needs to be changed regularly. It is easy to check and should be done before the walls are torn open."
Thank you, all.
Handyman on Call also appears in the Globe's Real Estate section on Sundays. Peter Hotton is available 1 to 6 p.m. Tuesdays to answer questions on house repair; call 617-929-2930. Hotton chats online about house matters 2 to 3 p.m. Thursdays, at Boston.com. Hotton can be reached at photton@globe.com. 
