I recently poured around 1400 square feet of concrete driveway at my home. I poured two sections first and then poured the third and final section in between the two. I used treated 1x’s as expansion joints between all of the sections. However, I have a number of reasonably large gaps (>1/2″) around the treated 1×4’s. I understand that water may cause the slab to fail if allowed to pour directly into these joints. Should I seal these gaps with something? And if so, what should I use? I thought that the weight of the new concrete would force the 1×4’s up against the existing slab, guess I was wrong.
Thanks
Replies
Pull all the 1x4's from the joints, and fill with foam backer rod and NP-1 caulk, or another high quality caulk sold for pavement use.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Where do I get foam backer rod? And how much backer should I put down before sealing the top with NP-1? Thanks for all of your help.
You can get backer rod at most lumberyards, or HD if ALL ELSE fails. Caulking for concrete should be available at the same yard. The backer rod is round foam cell in rolls and really helps save on the caulk.
ColeCole Dean
Dean Contracting
You can get the foam rod at HD and/or lowes, but you have to look hard or find someone who knows what it is.
There mfgrs provide pretty detasiled guidelines, but it would be safe to stuff the gap so that the caulk was about 1/4" thick, a little thinner for narrower joints. The purpose of the foam is not to reduce tha amount of caulk (although that is a side benefit), but rather to prevent the caulk from "three-sided adhesion". Caulk stretches with changes in temperature and flexure and whatever else causes the caulked items to move. The best situation is for it to be attached to only the two opposite sides, so that it is pulled in one direction. If you did not use the foam, then the gap/joint would get filled with caulk, and it would stick to both sides and the bottom. Then when the two items moved apart, the caulk would be trying to stretch to accomodate the movement, but the bottom of the caulk bead would be stuck in place. This will probably cause the caulk to get torn. The foam is soft enough that it tears when the caulk moves, but by then the caulk is cured and doesn't need the foam.
If you have a really big gap, you could fill it with spray expansion foam and let it cure overnight before caulking. In a pinch you could stuff the gap with newspaper or fiberglass insulation.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Trust me Ed, it was my last intent to send him to HD to buy backer rod. I'm sure he'll get sent to the plumbing dept. But they do have it, although my local yard also does, and I don't have to wade through 98 aisles to find it.
BTW, thanks for the rundown on it's purpose. I actually had no idea what function it served other than saving on caulk. Probably because on brands packaging says "caulksaver" on it.
I install alot of automatic gates, and usually we install traffic loops with them. 14 ga. wire in a single sawcut and sealed. One for free exit of the facility, and two safety loops to prohibit the gate from closing on a vehicle, and with about 300 lf of sawcut, the backer rod really has saved on the sealer, which is around $ 40 a tube. But I realize there are more benefits now.
Thanks for the heads up.
ColeCole Dean
Dean Contracting
Great explanation Ed.
Same lesson I learned at Tremco.
BTW I have never seen backer rod split from expansion of a joint. It generally just slides up and down in the joint as the bead of caulk flexes with movement. I have cut out some old joints and had the backer rod still stuck to the bottom of the caulk.
Another good source is a concrete form/steel supply vendor. Mine carries backer rod from 1/4" to 1 1/2".
Coledean;
You dont need to fill the joint completely with backer rod. Buy the size you need and shove it down just enough to give you the 1/4" thick joint in Eds' post. SL1 (self leveling) urethane caulk by Sonneborn should also be available at the conncrete materials supply source(about $11.00 fo a qt. tube). If you want to hide the joint, get a bag of sand and sprinkle it over the joint about 2 to 4 hours after you have caulked. (it will have started to cure /set by then. do it to early and the sand just sinks in the caulk).
Dave