Floor Tiling. Need lots of help.

[BigWallop]

Hi Peoples,

I am having a nightmare about laying floor tiles on an old (very old) suspended floor. I know that the floor is way over one hundred years old and is now nail sick and sagging. The joist ends are good and in position on their pads, of which a few have been changed, and all is fine with strength and soundness to keep us safe from falling into the downstairs neighbours kitchen.

The problem I am thinking of is deflection of the joists as they feel like the noggins are now loose, or have been cut by other trades over the years, and are not tight enough in place to prevent the bouncing like a trampoline.

We definitely can't move out of the house while the I lift the whole floor to strengthen it. And I don't really want to ask the neighbour if I can rip their ceiling down to fix our joists. Another worry is, if I start to fix the joists, How Much Damage, can I expect to be fixing on the neighbours latth and plaster ceiling. :-))

So the whole scenario goes like this.

The tiles are being laid to one end of the joists, out to about one and a half metres our from the wall.

What I'd like you guys help with is.

Is there a way to sort of isolate that end of the joists, and to strengthen them enough to be able to lay ceramic tiles successfully?

How much should I expect to be doing in repairs to the neighbours ceiling. (would a bribe help before I start the job?)

All suggestions, as long as they are clean and viable, will be most appreciably accepted.

Ta much for reading this.

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[harryagain]

You can buy backing board for situations like this. Looks/feels a bit like abestos sheet (but isn't) They have it at places like tiles RUs, maybe not B&Q. You screw it down on to floor boards etc & then have a good surface to tile to. I think a special flexible tile adhesive is used. You can pick their brains at the shop. It needs lots of screws

[BigWallop]

Ah Ha !!! Now that would be handy. I've looked at the cost of the flexible tile adhesive and WOW !!!!!!!! Almost triple the cost of standard sticky stuff. But I suppose if needs be.

I'm still a bit worried, even with the flexi' adhesive, that the joists will still bounce a bit to much. I might just go ahead and lift the flooring, above where the tiles are going, and set some noggins to help strengthen a little more.

Many thanks for the tips though. Another way of thinking is always helpful.

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[Dave Liquorice]

You are trying to fix something that is brittle and inflexable onto something that is flexing, recipe for disaster. The floor needs to be made firm donno of the board mentioned by another will do that or if it is only intended to make a smooth flat surface...

[BigWallop]

I had a look at the boards that Harry spoke about, and although they look like a great idea and will probably be used under the tiles, I think that they might be alright on an already firm floor. As you say, I'm more worried about the joists flexing in the middle when the kitchen/dining furniture is put back in place and people are walking across the floor.

These old joists are still sound, but they do move a bit when the weight is on them. I know the area being tiled is small (1.5m X 4m) in comparison to the whole floor area (7m X 5m in total), and that the tiles are to one supported end of the joists, but I'm still worried that the original noggins, almost certainly positioned just in the center of the 7m span, will be enough to stop the floor sagging and popping the tiles off. Especially the tiles along the edge.

I wonder if I should just suck it and see, and prepare for the worst from the right off.

Now............Does anyone know of a good timber merchant in the Edinburgh area? :-)

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[Tim Watts]

Sorry - misse dthe start of this...

Did anyone suggest 18mm ply sheet over the top, well screwed down and tile to that?

[BigWallop]

Thanks for that suggestion Tim, but 18mm would be a huge step up from the rest of the floor level (18mm + adhesive + tile), and would also mean cutting a lump off the bottom of a door. I'm still worried that even with some type of ply or screed boards laid to reinforce the part of the floor being tiled, even though my thought was to fix 6mm boards on top of the floorboards, that the joists themselves will bend enough over their length to pop the tiles back off.

Have done a bit research on adhesives, being normal cement based, resin reinforced and the full flexible stuff, and they all state that the worst situation they can withstand is up to 10mm deflection on the floor structure. I'm sure that these old joists are moving as much as that when we all gather in the room to chill out etc. I think it's time to gather the muster, and the time, to go ahead and explore the floor fully to make an informed decision on what to do.

Once more into the breach, dear friends. LOL

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[Tim Watts]

I've got a couple of bedroom floors with steps like that due to engineered wood over insulation panels on concrete. It's actually fine - but I put oak thresholds in and planed a chamfer on them to avoid having a trip hazard.

Trimming the door is easy - take it off and run a circular saw, a jigsaw or a handsaw over it :)

I think, given how you have described your floor, 18mm ply would be just on the edge of "will probably be OK". Any less (or none) and I'd give up and stick vinyl down!

Can you replace the floorboards with ply? Ply glued and screwed to the joists is a *lot* stiffer than boards so you buy more stiffness for your thickness. As you are tiling the floor, there's not much to be lost by gluing the ply too. But if that worries you, use screws every 10cm or so into every joist (not just round the edges of the ply).

You'd definately want the best flexible stuff - something made by BAL or Mapei. Some are "ready to mix" flexible, some are "regular" to which to buy and mix with a flexible additive liquid.

Don't forget, you'll want "flexible" grout too - I used Mapei Keracolor with Fugolastic additive when tiling over flexible substrates.

Cheers,

Tim

[BigWallop]

I really don't want a step up on to the tiled area, and to prevent that means boarding over the whole floor. Not an option this time.

Now then. That's an idea. Remove the old boards, which are quiet nail sick, and lay new chipboard flooring. These old boards are nearly an inch thick, so chipboard flooring matches better in thickness.

While I'm under that part of the floor, it;s easy to bash in a line of noggins to make the joist don't wobble. Thank you for that suggestion, Tim.

These little ideas are a big help. I think I got myself blinckered by the preparation needing done. But it's not a big job after all.

Many thanks Guys.

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[Tim Watts]

Ok - there's a plan then.

As I don't to be responsible when you come back in 3 months saying the tiles are cracking, here is what *I* would do:

While you have some of the floor up, go and buy some ply insmall section size (Wickes or B&Q sell cuts - you want the 2x4 foot size as it's small and cheap enough.

Remove enough boards to put that direct to joists, and screw every 10cm or so. Now you can do some deflection tests. Your worst enemy will be the washing machine on spin - the weight and dynamic loadings will be very high.

If your floorboards were 25mm thick, you could even consider going up a thickness in ply if it seems necessary. Depends a lot on your joist spacings but tiled floors are commonly done by tiling to ply over joists and I have seen at least one and that was fine.

Don't forget to have a plan about underfloor services - like not having them under the tiled area or you will regret it :-o

Cheers,

Tim