What to use to glue a (heavy) slab of slate to a cinder block?

I am trying to figure out what to use to glue down a slab of slate (weighs in around 160lbs) to a cinder block. It’s going to act as the outflow path for a small water fall, so it has to be a water proof bonding agent. Ive asked at the Home depot but I’m not really sure the girl was certain of her recommendation (Apparently she was just reading the signs over the shelves. :rolleyes: ).
The slate is stable on its base, and it doesn’t really move easily, but there will be little kids running around and I REALLY don’t want any accidents.
Any suggestion?

This morning I had to reset some slate tiles in my bathroom. The local tile supply house strongly recommended against using mastic or construction adhesive wtih slate, recommending instead a thinset mortar. It seemed to work.

I have to grout it tomorrow.

Mortar. And you might want to wet the cinderblock first, to discourage it from sucking the moisture out of the mortar before it cures.

Liquid nails make a heavy duty construction adhesive. The tube fits in a caulking gun and will adhere to practically any surface.
Just don’t use it on asphalt based roofing material ie: shingles, felt, rolled roofing etc. it will eat a hole through it.
A thinset mortar would probably work. However, it has a tendency to crack whereas the adhesive is very durable in that regard.

The finish on the slate should make the decision for you. If it is rough and/or porous then mortar should be fine. If it is very smooth and non-porous you should use an adhesive. Is there to be an angle or slope involved?

BTW, The L/Nails will adhere to either.

and… Why a cinder block? one or two more. Those damned things break pretty easy.

You did not provide size of slate slab nor where or how you plan to install it. Either or could affect how it is to be attached.

Consider using fired bricks or something a bit more solid and stable.
With both pieces absolutely dry I would use a mixed epoxy applied liberaly. Only if the joint is subject to mechanical shock would I use Liquid Nails or similar adhesive.

thought of mortar, but given that it will have water flowing over the top surface of the slate I feared that moisture might affect it. (To be precise, there will be no actual water anywhere near the juncture of the cinder block and the slate. At least so I hope, but I don’t know how porus the slate actually is, so i figured I should play it safe.) Also, I didn’t think mortar actually “glued” things in place. Am I wrong in that?

The slate is approx 2’ by 1.5’ and about 4-5’’ thick. Its just a piece of field stone I found that looked really nice so I wanted to use it.
I’m using cinder blocks cause I have them, they are easy to use, and the structure will not be subject to any sort of shocks (again, so I hope) so I don’t see how it could break. The blocks are secured to a concrete slab.

Basically the slate is going to be resting flat on top of the cinder block with the back end of it also resting on a thick concrete wall. Like I said, it’s very stable and unlikely to move easily. BUT there are small children around, and I REALLY would rather overkill with regards to securing the thing then risk any sort of accident.

You ever hit a brick wall? Mortar is STRONG. It’s identical in composition to concrete, only it’s mixed with slightly less water, to make it thicker, and sand is used instead of coarser gravel or crushed stone. The binder is the same for both–Portland cement. Once Portland cement has hydrated (cured), it’s extremely waterproof, if somewhat porous. It better be–Hoover Dam is made of the stuff.

**Q.E.D.**hydrated = cured You sure about that? Not saying you’re wrong, just asking? I’ve poured a lot of concrete and layed a lot of brick but I don’t recall anyone ever using that term. I know it is hydrated in order to become the pourable cement but I thought it had to be de-hydrated in order to cure (harden).
Just a thought.

Mortar/cement/concrete continue to cure indefinitely. The hardening/curing process continues after the initial set up and drying.

I’ve always considered mortar superior to adhesives and ‘sticky’ mastics, but the adhesives do help on vertical surfaces.

Mortar and mortar types are used on floors and showers.