Limestone onto old plaster

[scowps]

HI'm tiling a bathroom with some quite heavy limestone - I've been told about 25kg/m2, and the plaster on the brick walls is a bit knackered in places, and the skim has been painted with a bathroom paint.

Am I better to chop it all off and replaster, and if so what with - a cement based, one coat, or browning? Also how long do I wait for drying out before sealing (not with PVA!)

Advice much appreciated!
Steve

[peckers]

Hi there and welcome to the forum
Firstly the tiles weighing in at 25kg per m2 is to heavy to tile onto skimmed walls, also the bathroom paint isnt good to tile onto as it is waterproof and will stop the adhesive bonding to the walls.
It depends how bad the plastering is on the walls as to weather or not you knock it all off or not!
If you go down the route of knocking it all off back to brick then you could dob and dab plasterboard back on the walls and use mechanical fixings as well! Do Not re skim the plasterboard! Or you could use tile backer boards or have it rendered with sand and cement, again do not skim on the render as it is the skim that is the weak part!
You could also stud the walls off with timber or metal batens, the choice is yours!
If you do render the walls then the drying time is a factor to take into account as this will slow the job up as it can take between 2-6 weeks to dry properly before you can tile onto it!
Under coat plaster such as hardwall should not be tiled directly onto as it as an under coat for skim!
Not being able to see the job in hand it is difficult to say what is the best option to use, but if it was me i wouldn't render the walls as its a long process and for speed and good results i would use tile backer boards or dob and dab plasterboard!!
If you dont have to knock all the old plastering off and you have room you could overboard the existing with tilebacker boards or plasterboard and mechanical fixings, this would save the time of knocking it all off if you dont have to!!
I hope this helps good luck and post some piccys if you can!!

[Oli]

For that sort of weight id be looking at mechanically fixing cement boards to the walls.


You can find weight limit info in this thread.... http://www.tilersforums.co.uk/tiling-forum/13313-all-questions-i-asked-when-i.html

[dagger]

i would chop everything off and dot and dab plasterboard up everywhere,
its cheap and holds 40kg if you do not skim it, buy chamfered plasterboard and tape and join with plasterboard adhesive.

tank where necc.

[mags]

i would chop everything off and dot and dab plasterboard up everywhere,
its cheap and holds 40kg if you do not skim it, buy chamfered plasterboard and tape and join with plasterboard adhesive.

tank where necc.

Thats 32kg / m2 backer board is 40kg /m2

[dagger]

Thats 32kg / m2 backer board is 40kg /m2

i stand corrected. but it will do the job and cost hundreds less!

[mags]

i stand corrected. but it will do the job and cost hundreds less!

I agree wholeheartedly

[dagger]

limestone is actually one of the lightest natural stones avaliable,
so it may not even break 20kg, unless its 15/20mm.

[tileexperts]

i thought you never tile on paint anyway??? cause its a losely bonded surface?

i always tell my customers that the paint has to come off.

so am i wrong?? or can you actually tile on paint??

[dagger]

i thought you never tile on paint anyway??? cause its a losely bonded surface?

i always tell my customers that the paint has to come off.

so am i wrong?? or can you actually tile on paint??

in a word "no"

[Dave]

limestone is actually one of the lightest natural stones avaliable,
so it may not even break 20kg, unless its 15/20mm.

That depnds upon the limestone obviously....Applestone is 25.1kg a mtr and some others like bastille is very heavy..probs over 40kg....

So it is wise to weigh a tile and multiply by how many is in the mtr..and add about 3.5kg per mtr for adhesive and grout.

[dagger]

That depnds upon the limestone obviously....Applestone is 25.1kg a mtr and some others like bastille is very heavy..probs over 40kg....

So it is wise to weigh a tile and multiply by how many is in the mtr..and add about 3.5kg per mtr for adhesive and grout.

obviously, that is why i said "may not even"!

[scowps]

Thanks for the responses guys - I did a fair bit of phone bashing yesterday - the first conclusion was to set to chopping off the old plaster.

I can't board out as the depth I've got to play with is 30mm from brick face to finish face! (due to the position of the door frame)

I spoke to British Gypsum Tech, they said anything plaster based has a max weight of 20Kg/m2, I then spoke to BAL tech, who have a product called Quickset Render, a cement based render he assures me would easily take the weight and is tileable within 4hrs! (expensive though!), and Mapei also have a cement render called Nivoplan which although cheaper than the BAL is still quite expensive but again much shorter curing time than sand/cement.

I think I'll be going down the 'new product' route and give it a go! Not sure which yet though - I'll keep you posted