Concrete adhesion promoter?

I have a weird situation where I need to apply ceramic tile to a vertical cured concrete surface which has a 'bow' in it. So that means thinset or similar applied vertically, approximately 3/4" thick. Problem is, I need to be certain it's gonna stick and not later separate from the concrete. I see 'adhesion promoters', is that what I need? Or am I overthinking this whole thing?

I dunno about a vertical tile, but I've always have used a latex based adhesion promoter when dropping tile on concrete. I'd think if you used the latex and mixed the thin set stiff it might work.

Henry's makes a latex adhesion primer that works wonders on floors. I haven't used it on walls though.

Acrylic thinset should hang on just fine since it doesn't shrink.

C- I'll try and grab a TCNA (tile) manual when I get to the office to see what they recommend. I'm traveling right now.

Are you going to try to build the wall up to be dead straight? That seems risky to me...How big are the tiles, how low are the hollow areas, etc- I'd probably use good thinset and let the tiles follow the curve of the wall, at least a bit. If they are big tiles, you concern is going to be keeping them up until everything hardens, but I think that would be better than trying to get a skimcoat of concrete to stick. I've seen a lot of parging chip off over time, particularly on my house.

S2, thanks!

I am trying to get the bow as straight as possible. It's ~3/4" deep in the middle and tapers at the ends. The vertical face is about 8" tall, the length is about 12 feet. The tiles are 12" square, of course I would cut to the correct height. There will be a tile edge at the top.

I'm thinking: Tapcon a steel mesh to the concrete face. Apply thinset (that's where the adhesion promoter would come in, to help the thinset stick better to the original concrete). Tapcon another layer of steel mesh, but shorter, over the first layer of mesh and thinset then put more thinset on that mesh. At that point I should have it built out enough that the tiles could be laid straight, as viewed from above. Let this cure for a couple of days then thinset my tiles to that facing.

I have a small test area that's been curing a couple of weeks, I want to see how well the thinset sticks without adhesion promoter. Got my fingers crossed.

My concern with all this is that a lot of the time people step on the edge of something like this and I don't like the idea of the facing suddenly coming off.

I had a bad (expensive) experience with thinset concrete once. It was a big job and we had a lot of experts there trying to make half an inch of concrete stick to a thicker layer. Eventually the slab had to be broken up and replaced. It just would not stand up to traffic.

Another idea... Plaster the low spots flat, tapcon some 1/4" hardi-board on it, then do your 1/4" notch thinset to adhere the tiles. That way you're not fighting 3/4" thinset, lath, gravity, etc.

Or... another crazy idea that I've done before...

The 1/4" backer is more than strong enough to support the tile, even if you span across the low spots, but a good butt-bump would let it flex enough to crack the thinset or a tile. When I put backer up for my parents' shower tile, I drilled a few holes in it and squirted expanding foam behind it in the low spots. 4 years and no flex.

C- see your PMs when u get a chance. Some good insight above too.

Curmudgeon wrote: S2, thanks! I am trying to get the bow as straight as possible. It's ~3/4" deep in the middle and tapers at the ends. The vertical face is about 8" tall, the length is about 12 feet. The tiles are 12" square, of course I would cut to the correct height. There will be a tile edge at the top. I'm thinking: Tapcon a steel mesh to the concrete face. Apply thinset (that's where the adhesion promoter would come in, to help the thinset stick better to the original concrete). Tapcon another layer of steel mesh, but shorter, over the first layer of mesh and thinset then put more thinset on that mesh. At that point I should have it built out enough that the tiles could be laid straight, as viewed from above. Let this cure for a couple of days then thinset my tiles to that facing. I have a small test area that's been curing a couple of weeks, I want to see how well the thinset sticks without adhesion promoter. Got my fingers crossed. My concern with all this is that a lot of the time people step on the edge of something like this and I don't like the idea of the facing suddenly coming off.

+1 for wire the mesh. I used plaster wire mesh to build up my old clusterberkeleyed basement walls level, plumb, square. I used regular mortar mix to build the walls out, straight edge and level to plumb and a rub block to surface smooth. You could double the mesh under the deep spots but laying up mortar to 'bout 3/8" n let it set overnite then topping w/in 24 hrs while moist will work too. Don't try to fill 3/4" all at once. Mesh will eliminate cracks over large surface areas.

bearmtnmartin wrote: I had a bad (expensive) experience with thinset concrete once. It was a big job and we had a lot of experts there trying to make half an inch of concrete stick to a thicker layer. Eventually the slab had to be broken up and replaced. It just would not stand up to traffic.

This is what I'm worried about. I had a house with what looked like stucco on the foundation, in reality it was some sort of mortar 'smeared' over the concrete block ('cinderblock') foundation and pieces of it were coming off after 3-4 years. That wasn't done with thinset as near as I can tell.

I had to remove ~20 sq feet of old thinset where tile was set at the original entry way back in 1979, that stuff was a beeyotch to remove but it did eventually come off of the concrete. I think if what I'm looking to do sticks as well as that old thinset did I'll be in pretty good shape.

I would go with either of Curtis's recommendations.