PVA and Tiling over tiles

[buelligan]

...mm...very interesting reading...at the risk of being accused of hi-jacking this thread, I wonder if it would be possible to help me with some PVA related questions I have;  at the moment I have two diy projects that (may) involve the use of PVA.  I intend to re-tile a shower (and surrounding area). Rather than spend days removing all the original (modern, glossy) tiles, I was hoping to tile over them.  I was told that the old tiles should be scratched up and primed with a PVA/sand primer to give a good surface for the new tiles to bond to.  Is this correct?  I am also putting down some self-adhesive vinyl floor tiles on to an exterior ply sub-floor.  Should I prime the floor with dilute PVA?  Finally, and most importantly, what is PVA known as here in lovely France please?  Any help/advice would be most welcome!

[RicandJo]

Not sure what you're hi jacking but pva is generally known as colle blanc

Can't help with the tiling thing I hate tiling over tiles so I always pull the old ones off!

No need to pva the floor just put your vinyl tile glue straight on it.

[JohnRoss]

When I have tiled over tiles I have drilled lots of holes first in the old tiles and raked out the grout lines with a smallish masonry bit, worked for me in that no new tiles have ever dropped off. For small jobs I have used Coteka wood glue diluted as it is PVA I believe. I have also used resine d'accrochage, not dissimilar to PVA, over large areas before laying new tiles...................................................JR

[Andyphilpott]

I have often tiled over tiles - it makes a good base for the new tiles. No need to drill/scratch/bond the old tiles as that is really unnecessary unless you are a belt and braces afficionado!

If you are sceptical, just stick two tiles together with tile cement and try to separate them when the cement has set!

Just make sure they are clean and free from any soapy residues.

I have never laid vinyl floor tiles so cannot comment on that.

I always keep some Unibond PVA handy - it is so useful for so many things.

Andy

[liz]

It is always said that old tiling makes a very good base for new tiles and we have found this to be true..  We have tiled over old tiles on several occasions with excellent results.  No need for any elaborate preparation, simply clean off thoroughly to remove any soap or grease residue and get tiling!  You won't need PVA either. 

Liz

 

ps  Andy - Two minds with a single thought at the same time.  We must have been reading the same DIY manual [:)]

[buelligan]

Thanks for the advice!  I now feel confident enough to move forward on this.  With regard to the tiling over tiles thing, I have always removed old tiles in the past.  However, here, their removal would do more harm than good and as I have so many other projects to complete, I thought it might be best all round to take the "shorter route".  Thanks again to you all for taking the time to help.  Debs [:D]

[BIG MAC]

Couple of things to contemplate, Do not use PVA in this situation it will peel away and you will have a shower full of new tiles.

If you are working to a shower tray (New or old) the tiling will arrive on the lip of the tray (Allows for a nice seal so ensure the tray is well siliconed in, pre-tiling, if retaining old then a good opportunity to rake out old sealant and replace. Once tiled, grouted (Always use a decent waterproof grout out of a fresh bag) and dusted (This needs to be done a few times as the dust gets up in the air..wear a face mask!) once spotless you will be able to run a neat bead of sealant round the edge and this will look quite good.

Wherever there is an exposed edge ie 1/2 hieght or 1/2 height going to full height the edge presented will be correspondingly thicker so may require a moulding to make aesthetically pleasing (To my mind always looks orrible on a vertical)

Please consider...after tiling will the shower enclosure / door still fit?...common mistook this one!

Thicker tiling may also affect door architraves ( May need to remove and plant some timber behind to create a slightly wider lining before replacing and decorating) and wiring to sockets (latter unlikely but worth considering is there sufficient slack to put face plate back in and remember longer screws may be needed)

Ditto fitting shower valve (If concealed) will the pipework be able to meet the valve once new tiling installed.

Bon chance!

Edit as there's only so many of my typos that even I can live with!

[Gastines]

Big-Mac obviously is a Tradesman and gives sound advice. Only thing to add ,it helps if your tiles are not in line with the old tiles so your new joints overlap.

Regards.

[Rookery]

If tiling over existing tiles you first need to determine the extra weight you are adding. A gypsum plastered wall can take a total weight of 20kgs per sq mtr, plasterboard 32kgs. This is the total weight of the old tiles, adhesive and grout plus the new tiles, adhesive and grout. If the combined weight exceeds this, there is a risk of the lot pulling off the plaster. The existing tiles should be soundly fixed and cleaned. Sugar soap is good for this. The glaze on the existing tiles can be scored to provide a key but this is not absolutely necessary. The new tiles should be fixed with a polymer modified, cement based adhesive. This provides for a chemical bond between the new tiles and the existing glazed surface. Priming is not necessary. Weber make good adhesives as do Mapei. Check out their websites for more guidance. PVA should not be used when preparing for tiling. I know lots of people do but its still not the correct product. I've not fixed self-adhesive floor tiles but I cant see a need to prime the ply first, just make sure its dust free.

[BIG MAC]

[quote user="Rookery"]

If tiling over existing tiles you first need to determine the extra weight you are adding. A gypsum plastered wall can take a total weight of 20kgs per sq mtr, plasterboard 32kgs. This is the total weight of the old tiles, adhesive and grout plus the new tiles, adhesive and grout. If the combined weight exceeds this, there is a risk of the lot pulling off the plaster. The existing tiles should be soundly fixed and cleaned. Sugar soap is good for this. The glaze on the existing tiles can be scored to provide a key but this is not absolutely necessary. The new tiles should be fixed with a polymer modified, cement based adhesive. This provides for a chemical bond between the new tiles and the existing glazed surface. Priming is not necessary. Weber make good adhesives as do Mapei. Check out their websites for more guidance. PVA should not be used when preparing for tiling. I know lots of people do but its still not the correct product. I've not fixed self-adhesive floor tiles but I cant see a need to prime the ply first, just make sure its dust free.

[/quote]

Oh dear.......

20kgs per m2 however the load imposed by a tile isn't just carried by the surface beneath, they are in effect laid on top of each other end on end once grout is set. Existing tiles should be clean, no need for anything particularly special good quality kitchen cleaner or bleach helps kill mould spores. You will not achieve a chemical bond which effectively is the marrying of two surfaces ie like solvent weld and plastics. Cementitious adhesive relies largely on suction.and mechanical grip. The Anti PVA brigade will have us believe that the tile adhesive will make the PVA become live (Noting we are talking tiling onto plaster walls now rather than tile on tile!) it's a load of nonsense a thin coat of well diluted PVA will stabilise a plaster wall by being absorbed. any PVA which does become slightly 'live' dries just the same and forms a bond. PVA is still recommended by many adhesive manufacturers. And yes there are primers for thermoplastic floor tiles, not strictly neccessary, but available.

[Rookery]

As before, the information I give on the subject of wall and floor tiling is based on many years experience as a professional, trained tiler. Anyone doubting the information can check

here http://www.tiles.org.uk/help/answer-weight.shtml

here http://www.netweber.co.uk/tile-fixing/weber-products/problem-solutions/internal-floor/impervious-tiles-or-substrates.html#tab1

and here http://www.netweber.co.uk/tile-fixing/weber-products/problem-solutions/internal-walls/tiling-onto-plaster.html#tab1

Yes, many people will fix tiles in the manner of Big Mac and get away with it.

It doesn't make it right though.

[BIG MAC]

"Yes, many people will fix tiles in the manner of Big Mac and get away with it.

It doesn't make it right though"

Neither does it make it wrong. For those gullible or insecure enough there are plenty of expensive options out there.

 

[Chancer]

Big Mac

For a long while I have been trying to coin a phrase to describe the ever expanding genre of un-necessary, often useless and always expensive products sold offering in reality nothing more than hope.

Any ideas?

[BIG MAC]

We call 'em 'Snake oil' in these parts! ;-)