New deck - Area currently concrete tiles over sand base on top of concrete slab.

gday dr-307

the timber framing code makes provision for the posts to rest on a sole-plate, as opposed to being tied into a footing below the surface. depending on the height above ground, wind forces, construction, this may be a suitable and economical solution to your needs. the paving is there and it falls therefore substructure drainage is not an issue. if the whole area is paved & the overall height above ground is less than 1m then this may well be an option.

with the substructure you need to decide if you want to span further distances with less but more substantial footings, or vice-versa. something to remember - every stirrup you put in will cost you around $20 once you factor in time and materials - maybe a little more because you need to get through a bed of concrete 100 thick that presumably has been sitting there for some time - personally i would be trying to tie into this to take advantage of it. having said that, you need to verify that it is indeed 100thk and suitably strong - it may have been a wet mix because it was only ever intended as a layer under the pavers; but then, maybe the pavers were laid over the top of an existing slab to change the appearance? 100 thk does seem a little excessive for a paving bed...

speculation aside - to answer such a question, you must name names...
what are the dimensions? where is it being built? what type of timber are you using? at what spans? will there be a roof and will it be integral to the substructure or mounted afterwards? what about handrails? how (if at all) will you attach to the existing residence? what parts of the deck do you want to achieve yourself as opposed to how much will you sub out? can you weld? and finally, what is your budget?

here is some food for thought... all these posts have used discussed differing methods for bearing the load...

tall deck next to a pool
http://www.woodworkforums.com/showthread.php?t=58407

low-clearance, stirrups
http://www.woodworkforums.com/showthread.php?t=55825
http://www.woodworkforums.com/showthread.php?t=57608

low-clearance, many stirrups
http://www.woodworkforums.com/showthread.php?t=58502

footings into sandstone
http://www.woodworkforums.com/showthread.php?t=55187

telegraph poles
http://www.woodworkforums.com/showthread.php?t=47807

stumps on/in to concrete
http://www.woodworkforums.com/showthread.php?t=56136

stumps direct-buried
http://www.woodworkforums.com/showthread.php?t=58109


r's brynk

WHAT! You're quoting for a job and you don't know how to construct it... amazing.

gday bloke

i think bolting into the conc is the go. can you weld good? if you can weld then you can bolt the base-plates straight onto the conc & cut & weld the posts to the suitable angle.

another option - setting threaded rods plumb into the conc with chemical anchors then bolting the concrete base-plates onto the threaded rod. this method will require larger and thicker base-plates on the columns because you will need slotted holes on the base plates so you can get the angle right as it is extremely difficult to get every threaded rod spot on without using the base-plate as a guide. then you'll need to pack under the columns with steel plate then bolt the base-plates down tight. next step is to grout in around the base to protect the threaded rod & packers from rusting out.

not sure if this will be entirely suitable with the above method but, check out the uni-pier system from lysaght steel; here is a website with some pricing -

http://buybuildingsupplies.com.au/ly...1199_1201.html

r's brynk

Originally Posted by Dr - 307

Hi Brynk,
Thanks for you're reply. The problem is the fall of land on two planes. Can I bolt the post housing ( the shallow ones with the single hole under the cap) to the concrete and then cut the post / stump to length and angle? I just worried about nature and the fact that the deck will want to pull down the incline.

nah the post stirrups wont work. at the check out pryda's website http://www.pryda.com.au/catalog.php?...ors&conn=PS160 -

this connector only has two bolts so it will not be as strong; if you can find one with 4 bolt-holes (ie, 90 degrees apart on the base-plate) then this will be better one.

the slope is not a concern if you use the second method i described becase you drill the threaded rod into the conc so it is plumb, then slide the base-plate onto the threaded rod. gaps between underside of the base-plate & the ground level may be different at each threaded-rod (because the slope of the land below) but there will be packers underneath; another way i have seen it done is to use 2 nuts - one on each side of the base-plate.

chemical anchors would be better than expansion anchors especially into conc.

r's brynk

maybe a pic would help... after the post is packed & bolted, the remaining gap under the base-plate (sole-plate) is grouted in with a non-compressilble grout. if you went for an m16 rod then the resistance to shear would be more than sufficient - if this is done properly the pull-out strength will exceed 2 ton per fixing -

suitable chemical anchors - ramset chemset or powers are two that i have used successfully - any of the 2-pack 'injection' systems. when you drill the hole try not to go clear through the slab itself. leave some cover. it's not critical but it will be a better join because you won't lose any of the chem out the bottom of the hole.

this is the only process that i have encountered that works successfully - any deviation from this has generally (for me, anyway!) resulted in failure... once you start with the chemical anchor it is best to keep going otherwise the chems will set in the end of the nozzle & you will lose a good 10% when you have to replace it.

drill all your holes first, then clean them out thoroughly with a pipe-cleaner & an air-gun (close your eyes!) or a vacuum cleaner. set all your bolts down next to each hole.

fill each hole to the manufacturer's recc but it will be about 25-30% deep; in any case when you push the threaded rod in it will fill up out & around - you should see a little bit at the top of the rod-hole when you push it right the way in; any more and it is wasted.

if somehow you can build the frame without securing it to the slab this will make your life a little easier because you can build the frame, square it all up then drill your holes and set the bolts. if you do it this way put the nut & washer on before you push the rod into the hole. do one or two then recheck the rest of your posts to make sure they are still plumb.

whenever you set a rod be sure you have enough above the hole to fit a second nut on. this is a contingency incase one of the little buggers doesn't go in right. if it wobbles or moves up and down after it is set (even one minute later) then it is not set & it will need to come out - wind a second nut down onto the rod to lock the lower nut, then use a spanner to wind it out of the hole.

the chemical anchor technology is well proven and will give you what you need; your substructure will be locked into the slab itself & i have seen it proven time and again in industrial and commercial application.

r's brynk

If your concern with using the bolt down post stirrups is with the sloping concrete then how about grinding the concrete to get a flat and level area and then bolting the stirrup in?

Or how about Brynk's second suggestion of using the threaded rod and a stirrup with a base plate with four holes. With nuts above and below the baseplate by adjusting the nuts you will be able to get the stirrup perfectly level. Sort of like the rag and bolt assembly used for mounting light posts. If you can't find any stirrups with a larger base plate with four holes then you could quite easily get a plate welded to some of the Pryda ones.

Just reading back over your post it doesn't sound like there is much slope at all. 300mm over 5m? or 10M? (you don't provide dimensions, only 60m2) is very little.
How high off the ground will it be?
How many posts and at what spacing?

I think you may be over-analysing about this one...

yeah i see no issue with sloping the post stirrups - the only show stopper is the fact that you slope on two planes & this stirrup is fixed on one axis; you would need to check out the post itself & this would reduce the overall size of your post to the neat dimensions of the remainder of the post in the area of the cut (the now weakest point).

you could rotate the post until the angle is right for both planes of slope however this would mean that your bearers will not bolt neatly onto the side of the post.

consider yourself up on the amount of work required to dig through the concrete (since you have decided not to do it ) - now you need to decide between setting threaded rod or grinding conc. as loki suggested - choosing the one requiring the least amount of work.

i think both would be fine structurally. grinding conc takes a decent grinder & discs and drilling holes takes a decent masonry pilot & bit of sufficient size & length. both these bits of gear can be hired; both methods will work well & more to the point both will be ok'd retrospectively by an engineer if approval is an issue.

r's brynk

Um Guys - why not put a small blob of pure cement paste under each stirrup to level/true it ? next day come along and fix stirrup down with a powerbolt or chem bolt.

Clean off the pavers and sand etc and wash down existing slab first.

I dont see what the problem is.

You will only need to grind an area less than 100mm x 100mm.
A diamond cutting wheel on a grinder will do this easily.

If you do it this way then check to ensure you are not creating an area for water to collect and eventually rust the post supports.

Pure cement mixed with water into a thick paste (stiff peaks stage) will structurally grout up to 35mm. Any thicker and you have to add 2 mm sand. You could add some bondcrete. If you are worried about adhesion to the existing slab scabble the surface a bit and keep it wet overnight then put down blobs of cement paste while concrete slab is damp but not shiny wet.

Yep sure could.