Advice from pro tiler needed

Hi,
i'm in the process of renewing my old kitchen. Floors , walls, cabinets and white goods.

First up is the floor.

The floor is 70% screed, 30% wooden suspended.

I have removed the floor boards and installed noggins between the joists, overlaid with 18mm ply and screwed down all edges. There are no edges that are not supported and all are screwed minimum 150mm mostly less that that.
Joists are 350mm apart.

I need some help now with a couple of questions before i go any further.

The wooden part of the floor is very firm, zero deflection, although i know that the screed and wood will move seperately.
The screed has a level change in it because old tiles were pulled up and from a high point on the timber floor the rest of the room varies between 5-8 mm lower in areas.

i am assuming i can make this up with. A levelling compound and adhesive.

Q: do i need to put a Decoupling matt down to ensure there will be no sideways stress on the tiles to prevent cracking?

I dont want to use a joint over the screed/wood line because that will spoil the look of the floor.

I had a tiler visit to get some idea, but he suggested i rip up the timber floor and screed, make up the floor void and then screed the entire room in one go.

That may be the ideal way to go, but i have to live in the house whilst the work is going on so cannot really do that. my preference would be to tile over existing, but obviously I want it to last so it needs to be done correctly based on what is present/possible.

There is a load of information about decoupling, adhesives, SLC etc etc, but its
Confusing, so I am hoping someone that knows, can advise me.

If the floor has to come up so be it, but if we can achieve a good result without it would be easier to deal with.

Sorry for the long post but appreciate any advice.

( tiles will be porcellin large format)

Steve28

 

What is the joist size & unsupported span? Whilst 18mm WBP is usually sufficient for light load/use areas such as bath/shower rooms, it’s advisable to use 22mm or 25mm WBP in a heavy load/use area such as a kitchen. What’s under & supporting the suspended floor, is the void vented to open atmosphere?

You must use WBP not standard ply & should acrylic prime the underside & edges but depending on your answer to the above, you may need to do more to prevent any chance of moisture ingress into the underside of the ply which will cause warping & tile failure.

Whist local hollows can be filled using cement based adhesive, for general leveling of an uneven floor use an SLC. Do not use conventional sand/cement screed.

You definitely need an uncoupling membrane.

What size/shape is the tiled area? With linear tile runs greater than 6m or odd shaped areas, an expansion gap may be advisable.

Taking up the suspended floor & laying a new screed may be the best option & probably the way I would go, it may even be a cheaper option. It’s the best way of minimising the risk of differential movement. You may still need an uncoupling membrane over the two slabs, being cast at different times they may still suffer differential movement which will cause tile failure unless you use an expansion joint between the two. A new sand/cement cast screed must be left to fully cure & dry out before you tile or you will have problems; this is a minimum of 28 days to cure but allow one day per mm of screed thickness to dry out; test for any residual dampness before you tile.

How large is large? The larger the tiles the flatter the tile base needs to be.

 

right im not a tiler, far from it actually but was just loooking and thought could you not overboard the whole lot with say 6mm wbp ply and then tile from there or would there be to much of a step into the room if you did that?

 

Karis,

Thanks formyour reply.

To answer your questions,

Joists re 4 x 2. And are in two sections. One side of ech is supported on dwarf walls, and in the middle they crossover , again supported on a dwarf wall. I have fixed them together where they cross with 3" screws from either side. The middle dwarf wall is approx 1m from the supports either side ( not quite in the middle). The void is vented since the rest of the house is also suspended floors with bricks out of support walls to allow airflow.

The board is 18mm marine ply.

The timber area is 2.5m x 2.25m. The total tiled area will be 5m x 3.6m in a rectangle.

Tile size is 60cm x 60cm.

If i rip up the timber and fill the void, then screed it, will it be best to use SLC over the entire area once dry?


Pvms, thanks, I dont want to overboard because i have height restrictions where the kitchen floor meets the hallway and adding 6mm to. Tile and adhesive would create quite a step.

 

The span is OK for that size joist but in a high load/use area such as a kitchen, I would have gone to 22mm ply. An externally vented void will mean the underside of the ply is exposed to varying humidity levels & the possibility of moisture ingress. You must seal the underside & edges of the ply thoroughly as any difference in moisture content between the top & bottom ply veneers may cause it to warp/curl & cause tile failure.

It’s worth remembering that you don’t really need marine ply. WBP is sufficient & cheaper, it’s made using the same waterproof veneer adhesives but without quality/decorative facing veneers of marine ply which you don’t need.

That size floor won’t be a problem as far as expansion goes. Use a large format trowel & a powder cement based adhesive. Use quality trade tiling materials, cheap DIY products are mostly crap. Use a flexible addhesive & grout over the whole floor.

Use an SLC to finish level the whole floor &, for belt & braces, I would still advise an uncoupling membrane. Make sure you install a damp membrane in the new screed & don’t restrict ventilation to the remaining suspended floors in the property.

You don’t really need to overboard but sometimes a small step (6-10mm) is unavoidable, however, with the right threshold, its rarely noticeable or presents a tripping hazard.

 

Whilst 6mm tile backer boards are suitable for over boarding in many cases, a 6mm ply overboard is not. The minimum thickness specified by BS, the tiling association & all adhesive manufacturers is 15mm. However, 12mm is generally accepted as the minimum you should use. An SLC will also give a far superior tile base.

In the OP’s case, I am also be concerned about moisture affecting the underside of the suspended floor. 6mm ply or even a 6mm quality tile backer board isn’t going to hold it back if it warps.

 

Karis

Thanks again for your time to respond.

The kitchen void has no direct vent in the room. Nearest external vent is i adjacent room and air flow is through missing bricks in the dwarf walls. Same to the fron of the house and the hallway via vent under main door.


I have already screwed down the 18mm marine ply. I thought it had better waterproof qualities being "marine" so did not seal it. Do i really have to take up the zillions of screws to seal it? 22 would have been proud of the old scullery slab.

For leveling, i have looked at renovating screed, from mapei? Will that suffice, and should i just do that to fix up the screed side then latex over the lot with some other type?

Re the adhesive, any suggestions on which is best for the mix of wood and screed? Ditto the grout?

I want to do it right first time and have it last so willing to pay extra and i agree a bargain is not all its made out to be so will stay clear of cheaper adhesives.

Finally for the membrane, any suggestions on type, thinnest that would do the job? I really want to keep the floor rise as low as possible, ie 10mm tile plus adhesive.

 

Not sure I understand the first bit but the whole of the under floor void will be subject to the same humidity levels as it is vented to the external wall air vents via the “missing bricks” in the dwarf walls.

The only thing waterproof about Marine ply is the adhesive used to bond the ply veneers &, as I said previously, WBP (Weather/Water & Boil Proof) uses the same waterproof adhesives but doesn’t have the quality/decorative outer veneers. Both types of ply are still made from timber & timber will absorb moisture unless it’s sealed, this is the reason for sealing the underside & edges but do not seal the upper tile surface. Sealing should even be done in the case of an internal suspended floor to ensure stability but in your case it’s even more important as the underside of the unsealed ply will be exposed to varying ambient moisture levels which will occur in a floor void vented to the external environment. It’s also possible & I’ve often seen water pooling on the slab surface beneath suspended timber floors & this will make the under floor environment extremely damp.

It’s not a large area & weather or not you take up the ply to seal it is your decision; personally, I wouldn’t risk it.

Is the old scullery slab to remain (is it a separate room) or is it part of the floor you’re tiling over?

The Ultraplan is fine up to 30mm thick; you shouldn’t need to cover with additional latex screed. Follow the manufacturer’s instructions & ensure correct preparation.

I use BAL but others are Mapei (but not the Buildfix one sold in B&Q), Granfix, Ardex, Webber etc.

Dural durabase, Schluter Ditra matting Norcros Permalayer. An uncoupling membrane + adhesive will typically add 3-5mm & the tile adhesive for large format tiles requiring a thick solid adhesive bed will add another 4-6mm + the tile thickness.

 

I meant that in the kitchen void there is no vent within the void itself to the outside, but there is one on the other side of the partition wall in an adjacent room. Regardless there will still be the same external conditions in all voids be ause as you say its all eventually open to the elements.

The scullery itself is in the corner of the kitchen. 1920's house so thats why its part slab and part timber. The extended section of kitchen is 125-150mm screed over a slab. I want to tile over all the new screeded part, about a 1.8m x 600mm part of the slab and the 2.25 x 2.5 m timber section.

Ok, youve convinced me to. Unscrew the ply and seal it. Having gone to all the trouble i would hate it to fil becuse of this simple fix. annoying and time consuming but better than having to redo the floor. Any special sealant or a varnish etc?

So once i have done that, i can use ultraplan to go over the lot. When dry stick down. Membrane thats the thinest available to avoid height.

The timber / scullery part is pretty level, but the newer screeded area has variations between 3-8mm where the old tiles have been pulled up hence the need to level. I think tht once done the whole rea will be pretty flat.

Is there an SLC thats better than others for leveling or do they all need to be trowelled?

 

If it’s part of the floor being tiled, the SLC would have made up the 4mm difference.

A wise decision IMO. This is what I use; http://www.bal-adhesives.co.uk/products/bond-sbr

Once you’ve re-laid the ply, prime over the top of all the board joints & apply reinforcing tape over the joint. I use fibre glass plasterboard tape in 3 overlapping strips. Work tile adhesive well into the tape mesh just as you tile. Follow the adhesive manufacturer’s instructions with regard to any priming of the tile surface.

Sounds good.

Practically all SLC’s will need troweling to some extent to help them along but you should allow a minimum 3mm depth overall to ensure a perfectly flat surface. Most SLC's don't provide a hard wearing surface so it's important you don't keep walking all over it before you tile.

 

Just to make sure i have this all correct.

1 lift boards, seal bottom and edges ( i have weber PR360) and screw down again.

2, prime the ply on the top, and stick down plasters tape along all joints between ply sheets and the screed/slab. (i have that too)

3, coat the entire surface with SLC (ultraplan renovation screed?) to level the surface out.

Is that correct? If so the tape joints will be under the SLC now so presume thats ok.

4, put down uncoupling mat, (thinest i can find)

5, wait for the matt to set then get on with tiling using a powdered flexible ahesive.

 

I only use BAL products which in this case would be BAL Bond. Webber is a good name & PR360 is a tile primer for sure but I don’t know about it’s waterproofing qualities; I suggest you check with Webber.

Generally, I never advise mixing products from different manufacturers as you can never be entirely sure how they will react with each other.

As long as it's a fibreglass mesh tape & not paper! Only prime the join & bit where the tape is going unless the addy manufacturer recommends priming the whole tile surface.

OK.

Yes.

Mats tend to be much the same thickness which will be 3-5mm when you include the adhesive.

Yes but follow the mat manufacturer’s instructions & you generally only get what you pay for with this stuff so pick a good one. A Rapidset adhesive is generally all I use but if you’re concerned about the 30-45 minute pot life, pick a single part flexible adhesive instead. It has a much longer pot life & you won’t be able to grout for 16-24 hours but you probably won’t be concerned about that.

 

Thanks again for all the information.

Ill now set to it and get some before and after photos. Probably take me a couple of weeks to finish since once the floor is prepared theres still the issue of getting mission control to choose the tile. I know the size and makeup but not the shade.

My tape is the fibreglass type so not an issue but i will check the weber site re the PR360. It comes with their tanking system so assume its waterproof.

Re you only use BAl products and not to mix, is there a compatible type of bal product to. Match the. Mapei Ultraplan renovation screed, and the correct type of powder adhesive to match?
I want to leave no stone unturned so if you have a preferred component list ill shop around.

 

Be aware that polished (unglazed) porcelain tiles may require sealing before laying, again before grouting to avoid staining & again in use but some tiles come pre-sealed. Check with your supplier but if in doubt do a water absorption test. Depending on the colour you choose you may need to use white adhesive rather than grey. For a kitchen floor, I would personally avoid unglazed porcelain or natural stone & do not use white or light colour grout as it will look pretty awfully pretty quickly. When compared to ceramics, porcelain is much harder so you will need a decent budget wet tile cutter especially on tiles that size. Lay the tiles with a minimum 3mm gap.

Using BAL products I would pick http://www.bal-adhesives.co.uk/products/fibrebase for the SLC + http://www.bal-adhesives.co.uk/products/bond-sbr to seal the back & edges of the ply + http://www.bal-adhesives.co.uk/products/prime-apd to prime for the SLC.

For the tile adhesive I would use Rapidset Flexible http://www.bal-adhesives.co.uk/products/rapidset-flexible but SPF http://www.bal-adhesives.co.uk/products/single-part-flexible might be better if you’re uncomfortable with a 40 minute pot life.

For the grout I use http://www.bal-adhesives.co.uk/products/microflex-wide-joint but it only comes in 3 colours.

 

karis

I think we are looking at a matt finish From Rovic. Beige ish.

Ill check but i think its sealed, if not i'll ask about sealing them.

Thanks very much for all the time you have taken to respond to my questions.

You have been a great help and just goes to show that there are people still happy to share their expertise without having to be paid.

Where abouts in the country are you located?

 

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