Hi Victor, I will begin by saying I have very limited experience with ceramic flooring. My understanding though from studying the subject a little and why I don't have any here is:
Laying tile on a wooden substrate presents two problems, both related to movement of the wood. The first is expansion and contraction of the wood with changes in humidity and to a lesser extent the movement of the tile and it's bed due mostly to temperature. The other is movement due to flex, as you say, movement caused as you move across the floor causing shifting. If the floor tends to shudder as you stomp about then you need reinforcement under it, sistering additional joists or additional posts holding it up from underneath. This isn't probably practical. Unless the floor feels a little spongy and it seems to be spaced like between the joists then replacing the decking won't likely make a lot of difference. On the other hand a couple or four sheets of good dense plywood will only add a couple of hundred dollars of cost and it is an option to be left open. It is possible that some part of the floor has got wet at some time and has deteriorated under the tiles which should become obvious when the mortar bed is removed. If there is already a transition up to the tiles and building it up a little higher with thicker plywood subfloor you might also consider that. Usually 5/8ths is used, you could go to quarter inch or even thicker at a little more cost but a lot more rigidity. If the joists though are deflecting as you walk about this won't help. While they have the wood up though you might be able to sister in more wood or gain some additional rigidity by cross bracing between the joists at fairly close intervals. The builders won't like doing it much and will probably have to use 'X' braces to allow for wiring or pipes, you could also use short lengths, 14 and a quarter inches or so long lengths of the joist material 2 by 10 or what ever where there are no obstructions like pipes though. Additional bracing will significantly reduce deflection of the joists and help to share what does exist across adjacent joists. If you line the bracing up near end-to-end any deflection can be nearly eliminated. Finally, I have seen several times on those television programmes where they lay down a rubber like membrane over the wood subfloor before the bed of mortar into which the tiles are set. This is to eliminate the sheering force between the moving wood surface and the rigid and inflexible mortar and tiles. The membrane sheers and not the bond between the wood and the mortar. this apparently substantially reduces the failure rate of the mortar bed which will substantially improve the tile bond and reduce the opportunity for cracking and failure. Now I have never known anyone around here to have used it, most though have only used ceramic tiles in small areas like entrance ways and such and none I know have had it long. It may be common in the city where there is a lot more ceramic tile used but it is something you might like to ask about. That is about everything I know about the subject and remember I don't have any direct experience, it is what I would do in your position. I hope this helps if even just a little. Dale Leavens, Cochrane Ontario Canada [EMAIL PROTECTED] Skype DaleLeavens Come and meet Aurora, Nakita and Nanook at our polar bear habitat. ----- Original Message ----- From: Victor Gouveia To: Blind Handyman Listserv Sent: Friday, June 29, 2007 6:09 AM Subject: [BlindHandyMan] To Scratch or Not To Scratch Hi Folks, Had a contractor here yesterday, two in fact, and each gives me their own interpretation of something I need done to my kitchen floor, so I'm wondering what you all think. I'm going to be replacing the ceramic tiles on my kitchen floor upstairs. I'm going to be laying thicker tiles down than I already have up there, as my current floor tiles are all cracked and coming up. Suffice it to say, this is a long time in coming. In any case, like I said above, I get a different story, as to how to go about installing the floor from each of the contractors. One says that I should rip everything up, and just lay down three quarter or five eighths inch plywood without any scratch coat, and I should be fine. The other says that I really don't need to rip up the sub-floor, as it feels sturdy to him, and that all you need to do is apply a good scratch coat to it, and install the new tiles. As some of you may or may not know, I'm a pretty hefty guy, weighing in at around 375, so this floor will have to put up with a heavy weight. Add to that the fact that this is the main kitchen for the house, so we're talking a great deal of traffic and with a five year-old running around, we're bound to get some spills and food stuff on the floor. Hell, I'm not that clean an eater either. In any case, which contractor is right. Can you make an argument for going with the scratch coat alone, or ripping up the sub-floor altogether and installing the plywood without the scratch coat? I should also note that the scratch coat would also entail laying down the wire mesh, so I guess that would make the scratch coat even stronger, but I'm still hesitant to do this, as I have had two contractors tell me that I should rip up the sub-floor in the kitchen and start from the bottom up. Any ideas? Victor Gouveia [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
