Confused about back buttering

[Brad]

Hi all.....

am still unsure about this whole back buttering thing......i have always understood that trowelled addy creates air pockets allowing the addy to dry...if on large format tiles the recommendation is to back butter both substrate and tile, would this not effectively create a bed of addy with no air pockets, making it difficult for the addy to cure properly?

also, as porcelain tiles are not porous like ceramic, it is not good practice to back skim them regardless of the tile size?

 

[Ian]

A cement based adhesive does not need any air to dry, it sets by chemical reaction (it will cure under water). So the whole point of back skimming/buttering is to create a solid bed with no air pockets in gaining 100% coverage between the tile and substrate. You should not be using dispersion adhesive (ready mixed in a tub) on large format tiles as this does require air to dry out, most tilers on here will tell you that they don't even use ready mixed adhesive anymore, possibly only for a kitchen splash back with 10x10 tiles. Does that help explanation help a little more? If some of it doesn't make sense just ask some more questions and I/we will be happy to help.

 

[Brad]

thanks for that Bri. I understand that rapid addy dries by chemical means so no need for air pockets. But what about an open time cement based addy such as Keraflex? I have always understood that the open time addy's dry through water dispersion, hence needing air to dry??

 

[Ian]

No mate, same principle as rapid set, just takes longer. Next time you mix some up, put a blob in a bucket of water and look at it the next day, it will be solid.

 

[Diamond Pool Finishers]

it's as the guys above have said, here is a job where you can see the back-buttering of tiles being fixed take a look
DIAMOND POOL FINISHERS ,COMMERCIAL WORK - YouTube
a swimming pool we did at christmas,

 

[Brad]

Thanks for that Bri. I learned something new today!

What would your advice be on back skimming tiles? Presuming your substrate is straight/level, would you back skim every tile (even a 150x150 ceramic tile)? That would seem like overkill to me, for a ceramic tile. However, my reasoning on porcelain tiles is that because they are non-porous, regardless of their size, it would be good practice to back skim. If that makes sense??

 

[Brad]

thanks for that mate. good video. what grout did you use on this job, and was it sealed in any way?

 

[Dan]

I always used to say you only need to back-butter/skim tiles that are translucent and only really due to you seeing 'ribs' through the tile in certain light if it wasn't 100% covered. But then stones came in that required you to skim them to fill small voids, for similar reasons as above.

6 x 6" ceramics don't need to be back buttered.

Most things on walls don't either unless the tile type requires it.

Floors might be a bit different as you want to get 100% coverage which ensures you don't have weak spots should any weight be applied to the tile at some point or a sharp object get dropped on it on that very point. If you have 100% coverage, your tile becomes as strong as the substrate (unless you have soft stone etc then that's a bit different).

You don't need to go silly with the back buttering though it's time consuming so only do it where applicable.

 

[Brad]

Thanks Dan. You say to back butter/skim the tile if "the tile type requires it". Could you elaborate. Sorry if i'm overthinking this whole thing, it's the way my head works. Ta.

 

[Diamond Pool Finishers]

thanks for that mate. good video. what grout did you use on this job, and was it sealed in any way?

thanks brad we back-butterd as we needed to make sure each of the tile's stayed in place real-good, as also it was a commercial job and if anything was to go wrong they would sue the hell out of us lol

 

[Dan]

Thanks Dan. You say to back butter/skim the tile if "the tile type requires it". Could you elaborate. Sorry if i'm overthinking this whole thing, it's the way my head works. Ta.

Well, if the tile is a translucent marble, and you hadn't back-buttered it, and you ended up with some trowel lines still in the adhesive when you pressed the tile into it, once you'd finished the job and the adhesive had dried, you risk being able to see them through the tile in certain light conditions. Not what the customer wants!

If the tile is a soft tile, you would want to do it so that you had no weak spots.

If the tile had voids you needed to fill, you'd want to do it then too for similar reasons to both of the above.