tile adhesive directly on hollow blocks

[lager]

hi what would happen if you apply tile adhesive directly to hollow block walls without applying mortar first? can the 1 inch thick tile adhesive function as the 1 inch mortar already?

 

[hokie66]

Tile adhesive is not applied that thick. You apply it with a toothed trowel, usually a 6 mm tooth for wall tiling. If your wall is regular, you can tile over blockwork, otherwise it is best to provide an underlayment of fibre cement sheet.

 

[lager]

what happen if it would be applied that thick directly on rough hollow block? how does it behave compare to cement plaster?

 

[hokie66]

No idea, as I have never heard of it applied that thick, and don't even know if it is possible. What type tile adhesive are you talking about?

 

[lager]

its typical tile adhesive. in theory why cant it be applied thick since its also made of cement?

 

[jimstructures]

If you are talking about ceramic tile mastic, hokie66 is correct and it is applied with a toothed trowel as he described. I'm relatively sure that the cement in the mastic is not the same cement in mortar tile base. The tiles will likely sag before the adhesive hardens and cements the tile to the block wall. this experience has been gained from many ceramic tile jobs where the mastic was applied over tile backer board and cement fiber board as well as moisture resistant sheet rock.

Hope this helps.

Jim

 

[hokie66]

I'm not an expert on tiling, and this is probably not the best site for trade related questions, but I will try anyway. What you describe sounds like a Portland cement mortar used as a setting bed. This is common for floors, especially for stone and terrazzo tiles, but is unusual for wall tiling, at least in my experience. If you apply the mortar to a wall, it would more commonly be called plaster or render. I don't know what procedure you would use to keep wall tiles in place is applying them directly into this thickness material. If the plaster is allowed to dry, then you could do the tiling on the plaster with the use of a tile adhesive, selected for the exposure of the wall, and used in accordance with the manufacturer's directions.

 

[lager]

Thank you

 

[Ron]

I have reviewed your sketch and offer the following:

The portland cement plaster shown in the sketch is there to correct planar irregularities in the masonry wall. It provides a flat surface, if applied correctly, to receive the tile adhesive. While both are cementitious materials, they are formulated for different purposes and serve different purposes on the wall. Neither the portland cement plaster nor the tile adhesive should be placed in thick layers. They are not formulated for that. Here's why.....

The portland cement plaster usually only has one or two additives (in addition to sand and portland cement) to improve its properties for placement and performance. Those two additives are lime and an air entraining admixture, both to improve workability and water retentivity. The portland cement plaster must be placed in at least two layers or coats, each coat having a thickness of about 8-10mm. The additives in portland cement plaster are formulated such that it dries (sets up) rather quickly to prevent slumping and sagging. The first layer is placed at 8-10mm thick and then scored or scratched horizontally. This serves two purposes. The first is to further reduce the weight of the layer and help prevent its debonding from the relatively smooth masonry substrate. The second purpose is to provide horizontal striations that give the second layer a mechanical and chemical bond to the first layer. The first layer is called the scratch coat and should be placed, then moist cured for 24 to 48 hours before applying the second layer. This allows minor cracking to occur in the horizontal scratches at close intervals that are not as likely to reflect through the second layer.

The second layer of portland cement plaster is then applied to the scratch coat and screeded to a flat surface to receive the tile adhesive. The second layer is also placed to a thickness of 8-10mm with the material worked into the horizontal scratches to provide the appropriate bond and to reduce the incidence of slumping and sagging while the plaster is still "plastic" or wet. The second layer should also be wet cured for 24 to 48 hours before applying the tile adhesive.

The tile adhesive, also cementitious, is formulated with more additives to provide a very fine surface, more workability, less shrinkage and more water retentivity (retention). Because of these properties, it cannot and should not be placed in a layer that exceeds 6 to 8mm and should then be scored as hokie66 described with a notched trowel. The trowel controls the thickness of the material to prevent sagging and the notches reduce the weight of the layer on the wall and provide an air gap that allows you to "seat" the tile for proper adhesion. If you place the adhesive in a layer that is too thick, it will slide down the wall, particularly after you apply the tile.

DO NOT PLACE THE TILE ADHESIVE IN A SINGLE LAYER TO REPLACE THE CEMENT PLASTER!!! It will not bond properly, will sag on the wall and you will have a mess of a job that will have to be done again, properly.

The sketch you provided appears to be from a material supplier of tile adhesive and other cementitious materials. Their sketch is the proper way to apply the tile. Do it that way, not the way you described that you'd like to do it. Yes, it requires more labor to accomplish properly, but at least you won't have to tear it out and do it again when it fails!

 

[Brad805]

In addition to Ron's comments, it is very difficult to place a wall tile into a thick surface and maintain a level surface. I suggest you leave the installation aspect to the installer and simply refer to the manufacturer's recommendations. In some cases where allowed to use mastic, that is what many installers prefer because it dries much faster and they can get small jobs completed in one day. Personally, I prefer thinset.

Mastic:

http://www.laticrete.com/Portals/0/datasheets/LDS0150.pdf

Thinset:

http://www.laticrete.com/Portals/0/datasheets/lds3170.pdf

 

[hokie66]

Interesting. I don't see a sketch.

One thing that tends to be confusing about tiling is the terminology. "Tile adhesive" comes in many types, which include what Brad calls "mastic", and also "thinset". Some adhesives are cementitious, others are not.

 

[Ron]

Hokie66....not sure what happened to the sketch. Gone now. It was from a supplier I'm fairly sure. Mentioned "ABC" products and was linked from abc.ph

Gave reasonable limits on cement plaster and thinset thicknesses.

OP mentioned that both were cementitious. If application is inside I would prefer acrylic or urethane adhesive.

 

[Ron]

Here's a link to the sketch originally provided by OP

Sketch from ABC