Leveling for a pier

[SteveInNZ]

I want to put a pier on to an existing concrete surface. The surface isn't particularly smooth and it has a 1 degree slope in two directions. I was thinking of having a base plate 500x500 and using 12 sleeve bolts to attach it to the concrete.

Since there could be 10mm gap between the plate and the concrete, plus say 5mm for the rough aggregate surface, what would be the best way to level the surface to bolt the pier on to ? Is that the way to do it, or should I have spacing washers under each bolt or something ? I'm not sure if leveling compound is intended to level that much.

Any suggestions appreciated.

Steve.

[traveller]

Build up a new slab on top of the existing slab.
Pre drill and insert threaded rods into the old slab. Then build a box the same size as your base plate or bigger, make sure the rods have plenty of clearance to poke through the new slab, then pour, much easier to level wet concrete than a dry one.
Bo

[SteveInNZ]

That makes sense. Would I be better to use a wedge anchor or anchoring epoxy into the existing slab ?
For that matter, would I be better to drill through the combined slab and epoxy for the full length ? I assume that the stud-epoxy-concrete bond would be stronger than stud-concrete.

Steve

[AndrewJ]

Gday Steve

Just set the pier on a centrally located shim such that there is about 1 inch of clear space under the base. Use the bolts under light tension to set the pier to the position you want then just use a dryish grout mix to pack fully under the baseplate. ( Google "Dry pack grout" )
Once dry, just tension the bolts properly
The rest of the 1 deg slope can then be left alone to assist with drainage.

Andrew

[troypiggo]

Another option would be to just use 3 or 4 bolts, and use levelling nuts under the baseplate. Wind them to level, then clamp the top nuts down on top, and finally dry pack grout under the baseplate for even bearing.

[speach]

There is a product that you can get from builders suppliers call leveling grout. It's specifically designed for this purpose. What you would do is level the pier and then pack this grout under the base plate, and as it dries it expands slightly to give a solid firm base. It used for getting the steel in an industrial building level and solid.

[ZeroID]

Rockite ...
I used it for rocket nozzles ...
It's non shrinking, goes off in about 20 mins, rock solid in 24 hours.

[SteveInNZ]

Are leveling grout, dry pack grout and expanding cement the same thing by different names ?

Rockite uses the term 'expanding cement' but the applications look more like the epoxy products I'd use to glue the studs into my base slab, rather than the volume filling described above. Is that correct ?

Steve.

[troypiggo]

Levelling grout is typically very runny/fluid so it self-levels, needs formwork around it until it sets.
Dry pack grout is a very dry mix, meant to be stuffed into the space from all sides and it stands up pretty well on its own.
Not entirely sure the intended use for Rockite is your application under a baseplate. That's not to say it can't be used there, just that it appears to be more of an epoxy bonding grout (ie glue) rather than a baseplate grout intended for even bearing.

[AndrewJ]

Gday Steve

Troy pretty much nailed it.
Levelling grout can be cement/polymer based, but mostly it is some form of pourable epoxy, and can be messy to use.
For small baseplates, a dry pack grout is the simplest and cheapest.
Specialised cement based "grouts" ( vs bog std mortars ) use ingredients that effectively prevent shrinkage as it sets, and allow it to get good strength in thin layers.
That said, i wouldnt use levelling nuts under the plate, as if there is any later shrinkage etc, you cant retension. A single shim/packer in the middle allows good grout penetration, and you can still retension later if required.

Andrew

[SteveInNZ]

Thanks. Better to ask and be sure than have all the 'experts' tell me I 'shouldn't have done that' once it's too late.

Steve.

[clive milne]

Steve... it depends on the design of the pier.

(can you post a picture of it?)


If the pier is well designed, with the bolt holes close to the webbing then I would just use (steel) spacers. If not, then I would definitely grout underneath the base plate.

[SteveInNZ]

The pier doesn't exist yet. There wasn't much point in working on that if I couldn't get a suitable surface to mount it on. I'm more concerned that the existing concrete is (was) the weak link and I think the solutions above address that quite well.

Steve.

[clive milne]

Well in that case, the simplest solution would be to fabricate the pier with the tilt built in to the base plate (and webbing).

~c

Incidentally... making the base plate much larger than the pipe diameter reduces the overall stiffness of the pier, unless of course you couple the bolts to the pipe with (tapered) webs.

This is how NOT to do it:
https://stargazerslounge.com/topic/61255-help-required-for-telescope-pier-top-plate-adaptor/

This is an example of where NOT to locate the bolt holes... they should be as close to the webs as possible.
http://homeobserv.co.uk/product/telescope-pier/

best
~c

[Terry B]

Don't be too obsessed with the pier. It should be reasonably vertical but it isn't that important. There should be very little lateral force on your pier when the scope is balanced on the pier and slewing creates very little lateral force. Most of the force is straight down. Stiffness is important as this reduces movement from wind etc on the scope.
The top of the pier doesn't have to be perfectly level either as you will adjust any error out when you polar align the mount. As long as the mount will balance safely on top of the pier it is ok. Think about a mount on a tripod. You can still easily polar align even if the tripod isn't level.