[TowerTalk] Drilling into a concrete slab

[Jim White, K4OJ]

Your home center's tool rental division should have what you need...work 
backwards from the hole size on the plate - it it is a little bigger 
than 1/2" you need 1/2" anchoring...tyipically this is down with a 
threaded rod - usually available from a nut and bolt house like a "House 
of Threads" or "East Armpit Bolt & Screw" etc... they will also sell the 
adhesive to set the bolts...opt for the best galvanizing option they 
have - these will have lots of water streaming past them might as well 
opt for hot dip galvanizing if available over a simple plating - and - 
certainly do not get "black" or unplated t-rod.

If you are going to anchor the rods in construction epoxy make sure that 
what you are drilling into is not just a thin slab - drilling a thin 
layer like that usually just creates cracks starter holes... If the pour 
is indeed deep then you can use the epoxy anchoring system... the 
manufacturer of the anchors will have a chart where you cross reference 
anchor bolt diameter, length and hole size and it will tell you how much 
epoxy and how big around the hole you should drill is....

I would recommend that as soon as all the bolts are shoved into the 
epoxy you lay the base plate on down - this will make sure that when the 
epoxy sets the bolts are indeed where you want them to be and not off 
 center forcing you to drill out the plate and in so doing upsetting the 
galvanizing...

You may also wish to attach the first section of tower to that plate and 
make sure that you are getting it started plumb - if the slab is typical 
of most it is not perfectly level (they do need to shed water, ya know) 
and just because that  plate sits tight down on it does not mean that it 
is going to provide you with the correct "take off angle" for you tower.

Some of the large drills [you will want a hammer drill and a masonry bit 
of the appropriate diameter (see above)] have bubble levels built into 
the housing to help you sight a plumb  hole - otherwise have friends 
watch you as you drill - someone a few feet away can detect 
non-verticality better than you can when your on top of the hammer drill...

ALSO - make sure that you know just where to put the base - you 
mentioned a bracket up 20 feet - that will move the tower out and away 
from the wall it is on - make sure you have calculated that in - again 
you may wish to bolt a few of these pieces of the tower and the bracket 
together and lean them up - this can be very revealing - plumbing the 
tower and then marking the slab is far easier than the option of 
re-inventing the base later!

Again, try and use the holes on the manufacturer's base - they will have 
galvanizing on them.

Have fun and wait for about 50 other e-mails from the Towertalkians!!!!

73,

Jim, K4OJ

Yup, just 51 days until the Florida QSO Party



 

Kenneth E. Harker wrote:

>     I am helping a university ham radio club with a tower installation
>on an already-poured level concrete slab.  It will probably be a 40' Rohn 
>45G tower bracketed once at about 20'.  We would like to put three or four 
>bolts in the slab and drill holes in a Rohn 45G base plate to match.
>
>     Can someone recommend a particular concrete anchor bolt and
>cement/epoxy/whatever product?
>
>     What needs to be done to drill the holes properly?  What kind of 
>drill and bit are needed, how do you keep the hole vertical, etc?
>
>  
>