Welding to a base plate

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Another carport question:One post will be 100 x 100 welded to an 8mm thick baseplate. The base plate will be bolted to a concrete driveway and packed underneath with concrete to the engineers specs.Now, I want to put the plate down first and then weld the post to it.The plate will be painted with a 2 pack epoxy undercoat and then an enamel topcoat.What I want to know is when I'm welding the post to the base plate whether the paint on the underneath side of the base plate will get too hot and fail? I want this thing to outlast me.The wall thickness of the post will be 5mm.Scott
Reply:Originally Posted by scott brunsdonAnother carport question:One post will be 100 x 100 welded to an 8mm thick baseplate. The base plate will be bolted to a concrete driveway and packed underneath with concrete to the engineers specs.Now, I want to put the plate down first and then weld the post to it.
Reply:What a pity. It would have been so much easier to get the plate down first and then attach the post. Thanks Wizard.
Reply:You can put the plate down first. I do it all the time. Precast has embedded plates and so does tilt wall. It the only way to do it...the only way. I set weld plates in concrete all the time. My own slab has four in it now. That is just SOP. Yes, on occasion we do get some exciting spalls, but that is just part of it. If you weld much tilt wall, you just learn to ignore it and move on.
Reply:The welding heat will definitely destroy the protection provided by the epoxy/enamel on the bottom of the plate.Do I understand correctly that you are going to mount and level the plate, then grout under it?  If so, or if you can arrange to do it that way, I don't think you have much of a proplem.  Mount the plate on its hold-down bolts with nuts above and below the plate so you can level it in position slightly elevated above the concrete.  Gap just enough to get grout under.  Weld the post to the base plate.  Swab 2-part epoxy under the plate to coat the bottom surface of the plate and the top surface of the concrete.  Grout.A properly selected 2-part epoxy can serve as a protective coating on the bottom of the plate AND as a bonding agent for the grout to the concrete slab.  You may want to provide recesses for the post bases in the concrete slab pour if this is a new slab.   In fact, why not use epoxy grout for such a small volume application under the post bases, IN ADDITION to the initial neat epoxy coating on the steel?  Properly selected epoxy is the best bonding agent for newly poured concrete to cured concrete.I believe that the epoxy PLUS enamel is overkill (but listen to your engineer), especially since there is no exposure to UV, which epoxy is not resistant to.awright
Reply:Weld them on with a 120V MIG.  That should ensure you don't get any heat that far!
Reply:Originally Posted by MAC702Weld them on with a 120V MIG.  That should ensure you don't get any heat that far!
Reply:Thanks guys.I'll still try and weld the post to the plate first, but it's good to know that if I end up putting the plate down first and then grout after welding all will be okay.It's going on a sloping, old slab, but if I can get a small quantity of epoxy grout (which I've never heard of) I'll use it.Scott
Reply:Epoxy grout is easy to find. SIKA is a worldwide supplier that has several types. They will have it at any good concrete supply house. A good non shrink grout would be ok as well. There are several that will hit 15,000 PSI in less than 100 hours.
Reply:Have you thought about galvanizing, prefab all the parts have them galvanized and simply bolt the whole thing together.Simonhttp://members.optusnet.com.au/~abba/index.html
Reply:Scott- Even if you dont drypack under the baseplate, welding with the plate direcly on the slab is no problem. Your post is 100mm square so the plates gotta be,what, 200-250mm square? The area that would be getting hot would be far enough from the edges that you would be in no danger at all. Sure, if you hold a torch right at the slab it will blow out or spall chips but that happens every day. I cut off 8 bolts today at ground level flush and didn't get any burns. They were 3/4 wedge anchors and if your quick and good its easy. The paint on the plate will burn off. If you bolt the plate down tight to the slab and then plumb your column tube to it, tack it, take it off and weld then paint, how can you go wrong? Keep us posted, we'll be glad to help(as you know)
Reply:I'm with Welder.man on this one Scott.Pre fabricate , galvanize and assemblejust remember to oversize your holes a bit.Far greater long term corrosion protection.Potentally better welds as you are controlling the position you are welding in.Easier to address mistakes when half of its not in the air.
Reply:There are two problems for me with getting things galvanised.1. Once the job gets too heavy, it gets a bit risky carting it round on the roof rack of the family wagon.2. The galvanisers are right out in the western suburbs. Getting there and back and avoiding peak hour means a half day exercise.I got the plate welded to the post. Bloody plate warped with the heat, too. It ended up being easier to NOT do it in situ. I'll bolt it in position after work one day this week. The bolts are in position just waiting for the baseplate and the nuts. I'm pretty sure the bolts are too small - 10mm gal Dynabolts - but by 5pm yesterday I didn't care.It's still going to be strong enough to park a car on top off, let alone underneath.The rest of the carport will take a while to get done. My elderly Greek neighbours are away and as the post was going on the boundary line I wanted to get it done before they came back - whenever they hear me drilling near their property they think I'm up to no good.Scott