confused with solid bed method

[Ruth]

The project is to lay pale limestone tiles, 12mm thick onto ply (have followed the advice with primed 18mm ply firmly fixed to boards) using Ardex 7001 flex adhesive. I have tried to figure out the next stage ie actually laying the tiles but am getting confused. I know it must be a thick bed solid bed method, but not sure exactly what that means. Do I spread an even layer of adhesive with a solid trowel then go over it with a rounded notched trowel, pressing right though to the board or leaving a few mm of complete coverage of adhesive? Does a 10mm notched trowel have a notch depth of 10mm and width of something greater? Is 10mm the correct size? (tiles of different sizes, largest 610 x 406, smallest 200 x 200)

I am aware of potential issues of permanant marking on the surface of a limestone tile if the under surface is not entirely covered with adhesive. I have read of back buttering the tiles, I presume this means spreading an even layer (assuming the tiles are flat) of adhesive before laying the tile. Is this necessary (I'd have thought more room for variation in adhesive thickness) or will they be sufficiently covered when placed (with a firm twist) onto the trowelled base? If so, how thick a layer?

Finally sealing the tiles, I thought it might be easier and safer to put one coat of sealant on the tiles before they are laid (LTP impregnator), is there any reason not to do this?

I really appreciate your advice, I wouldn't have got this far without it!

 

[mikethetile]

use a solid bed trowel and as you say back butter each tile

 

[aph257]

Thin Bed
Thick Bed

if floor is flat, i use a thin bed and back butter, if not then thick bed. if you work clean then use impregnater before and after grout.

 

[doug boardley]

Ruth a solid bed trowel is the one with the semi circular notches, so a 20mm diameter notch trowel will give you a bed of 10mm (the radius), with a twist of your tiles this probably compresses down to about 5mm of solid adhesive. Back skimmming a tile is using the un-notched side of the trowel and spreading a thin even layer, this ensures that you get no adhesive leaching through onto the face of your tile and also helps to ensure a 100% contact with the adhesive that's spread on the substrate.

 

[CJ CERAMICS]

now for the daft question.....but this one has always puzzled me....we back skim tiles to ensure 100% contact and stop adhesive leeching thru to the face of the tile? if we are applying adhesive to the back of tile to stop the spread adhesive from leeching thru what stops the adhesive we have back skimmed leeching thru??

 

[Stewart]

now for the daft question.....but this one has always puzzled me....we back skim tiles to ensure 100% contact and stop adhesive leeching thru to the face of the tile? if we are applying adhesive to the back of tile to stop the spread adhesive from leeching thru what stops the adhesive we have back skimmed leeching thru??

It doesn't matter, as it will all look the same because you've back skimmed.

 

[doug boardley]

back skimming is different to back buttering Chris, back buttering is where you comb the back of the tile, thus you can still get ribs showing through. I've always thought that if you back skim, it then allows the addy to disperse more evenly as you're not getting that initial impact of wet addy hitting a dry stone.

 

[CJ CERAMICS]

back skimming is different to back buttering Chris, back buttering is where you comb the back of the tile, thus you can still get ribs showing through. I've always thought that if you back skim, it then allows the addy to disperse more evenly as you're not getting that initial impact of wet addy hitting a dry stone.

thanks doug
the explanation makes sense .....having learn't to tile by working with another tiler he told about skimming to stop leeching etc ....but not how lol

 

[nybor62]

if you use a ptb pourable thick bed adhesive you will get 100% coverage use round notch trowel

 

[Ruth]

All of your replies are really useful, thanks. Doug, the skimming advice makes lots of sense, now I feel I know what I'm trying to do. Nybor, what is "ptb" pourable adhesive?

 

[aph257]

Thin Bed View attachment 21106
Thick Bed View attachment 21105

if floor is flat, i use a thin bed and back butter, if not then thick bed. if you work clean then use impregnater before and after grout.

I meant back Skim not back butter

 

[Ruth]

Thanks for your advice, aph. Am I right in assuming the trowel is pressed to the floor when spreading rather than leaving a layer underneath the notched adhesive? And would the skim on the back of the tile be a mere 3mm or so?

 

[aph257]

i press the trowel to spread on the floor and use the flat edge of the trowel to skim the back of the tile about 1mm thick.