sealing concrete joints


I have a concrete patio that consists of 4 sections, about 10 feet square each, and they are slightly shifting to create 1/2" spaces between them, and the house foundation too. (you can't see how far down the crack goes. seems deep) I had a tuckpointer here, and he mentioned that besides the work I originally called him about, he could fix this as well. As you can imagine, constant rainfall and freezing weather washes away dirt under the slabs, so over time I'm afraid this will get worse. The house (and maybe the slabs) are about 50 years old, and we live in the Midwest over clay soil. There is other evidence of shifting soil around here.
The tuckpointer said he'd use hot tar to seal things up in between the spaces. I wonder if that's a reasonable fix, or if I could use another material, perhaps even myself, to get a good result. Would silicon work in this situation? Other sealants?
LB
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If you can get the surfaces clean and dry then you should use Bostick 1100 FS. It is usually only available from construction suppliers, not the home stores. It sticks to concrete very well and it stays flexible permanently. I forget the stretch ratio but I think it may be as much as 25% to 40%. So a 1 inch crack could open to 1.25 or 1.40 inches and it would not tear. Tar will get hard and then it won't stretch at all so if the concrete moves at all it will open the crack again beside the tar. Be careful with the Bostick as any messes must be cleaned up right away with acetone or they will be permanent stains or lumps. It comes in normal size tubes so you could do it yourself. It is quite thick so if you have a lot to do it is hard on the wrists. I had a lot to do so I got a $20 power caulking gun that runs on compressed air. Needed a lot of adjusting of the air pressure so it wouldn't shoot out an entire tube in a few seconds.
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les wrote:

specific purpose...check out the big box store. I would not want tuckpointing for a patio where it freezes...should have some flex.
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They make backer foam rods and caulk for your problem. I believe you can get it at lowes. Comes in those bigger caulk tubes.
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If you can't get the backer foam, just buy a pool "noodle" and cut strips out of it lengthwise. All it's for is to limit the depth of the crack so you won't use so much elastomeric filler.
Nonny
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Hot tar is the old original standby. Current technology demands cleaning the concrete, installing backer rod to control the shape of the fill, and careful installation of one of the polyurethane caulks. Sonneborn's NP1 is a good one, use Vulkem or SL1 if you want to use self leveling material - your joints need to be fairly level for these to work, it really does seek level. There are some excellent 2 part silicone products, but the application kettles and equipment would not be feasible for a one time use.
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On 07/10/2010 12:48 PM, DanG wrote:

Just curious, do these work like silicone caulks where if you use them once you can't go back to the old school stuff because nothing else will adhere to the substrate?
nate
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