View Full Version : steel post on existing concrete
30th Mar 2011, 10:49 PM
I am about to place and dynabolt 4 posts that have welded baseplates to existing concrete. I am very inclined to grind the area of concrete for each post level so the posts secure somewhat plumb. This surely is a common problem but I admit to not knowing what mixtures may be available to take up the slack under the baseplate and maybe even act as a moisture barrier. I don't think levelling compounds or tile adhesives are a good answer but then I have little to no experience with this. Long ago someone suggested liquid nails to me but I am not inclined to agree. I am searching for something as I prefer the baseplate spread the load evenly without fracturing the filler. My best guess at the moment is tile adhesive with an admixture like bondcrete. Any advice would be welcomed.
30th Mar 2011, 11:06 PM
do you know how deep the concrete is you are dynabolting to?
assuming the unevenness is not extreme, your filler would be fairly thin which might be hard to adhere to the concrete and not break down with the weight of the post.
i would grind the slab to flat around the post area if there was a reasonable amount of meat to the slab.
can you cut the slab away at the post completely and re-cement to flat in that area? that way could cement to a reasonable depth and cement in a flat plate you could bolt to.
30th Mar 2011, 11:26 PM
if your concrete is a decent footing ie over 300mm thick, then drill the holes that line up with the base plate holes. Use chemset to fix your bolt starters (or threaded rod) into the slab. Then put nuts and washers on the bolts which will act as "levelling nuts" for the baseplae. Put the baseplate over the nuts, level then tighten with another nut and washer over the top. The gap between the slab and the bottom of the baseplate can then be filled with some morter mix or similar. If your slab is only 100mm thick, I would seriously consider cutting out where your posts are going and digging a footing. Also depends on the load your posts are holding up......
30th Mar 2011, 11:38 PM
The slab is 100mm reinforced and the posts support a stratco deck roof. The baseplate is likely to be around 400x400. Chembolts are to be used. Even if I try and even it up using washers (good idea as the slope is minimal) this won't get it dead plumb unless I am lucky. A bit more tedious grinding will get it close though. I suspect this combined with a tile adhesive mix will get the best result!
31st Mar 2011, 09:38 AM
Use non shrink grout, align the plate with your holes ,fit the bolts but do not tighten them ,go around the base plate with metal wedges until your post is completly plumb then pack the underside of plate with non shrink grout, its better to leave about 10mm under the plate makes it easier to push the grout in. tighten the bolts and check plumb, use the wedges for any adjustment. When dry remove wedges and fill gaps . ps non shrink grout has nothing to do with tiling it is designed for this sort of usage
31st Mar 2011, 09:51 AM
The baseplate is likely to be around 400x400.
What size are the posts that need a baseplate so big, it only needs to be big enough to allow for bolting.
The smaller the base the less packing or grinding will be required.
31st Mar 2011, 11:51 AM
As he says.
Use non shrink grout ....
This is the correct product for the job, a 10 - 35 mm gap between the plate and the concrete makes height adjustment and grout placement easy.
This is the product I have been using under all my columns for the house.
This is the jig I made for leveling and positioning the column before grout placement. Overkill I know, but it makes life easy and I don't have to worry about knocking a wedge out while I ram in the grout.
31st Mar 2011, 12:56 PM
Fantastic info...thanks a lot. Rang Construction Chemicals about the non shrink grout and it is the go. Next problem is actually getting the grout as few seem to stock it.
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