How Deep to Cut Expansion Joints for Caulking

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Old 09-10-10, 02:30 PM
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How Deep to Cut Expansion Joints for Caulking

I have a newly poured concrete slab with a bunch of expansion joints. My contractor said I could save a bunch of money by grinding out and caulking the joints myself. He was going to show me how to do it, but we had a falling out over a different part of the job.

I was wondering how deep and how wide I needed to grind out the expansion joints in order to caulk them. I'd like to have a clean seal on my concrete floors for sanitation purposes..
 
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Old 09-10-10, 02:42 PM
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I assume you are talking about control joints to control where shrinkage cracks occur. The joints should be sawed late the same day of the pour or early the next day. The rule of thumb is to make them about 1/3 of the slab thickness.

Doing it later is more difficult and not as effective since the cracks may have already started to propegate.

Dick
 
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Old 09-10-10, 03:40 PM
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No I am actually talking about full expansion joints, not saw cut control joints. I had multiple slabs poured and joints were put in between each slab. Right now there is a thin layer of concrete over the joints from the pour. I want to put caulk where the joints are so that there is a better seal over them and so that the floor is more sanitary. In order to do that I need to carve out a channel for the caulk to go into. I'm wondering if I need to cut deeply into the joint in order to fill the caulk in.
 

Last edited by waltercat; 09-10-10 at 04:06 PM.
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Old 09-10-10, 04:07 PM
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I just tested it out and ground down 1/4" It seems like doing a bead of caulk over that should suffice.
 
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Old 09-10-10, 04:20 PM
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I'm curious walter....what material constitutes the joints? I've never seen concrete placed over a joint of any sort..unless it was just by accident. They are either divided by some sort of wood or other material...or grooved in while the mix is soft....or cut in after.
 
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Old 09-10-10, 08:52 PM
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It is basically something sort of paper like material like this:

Reflectix EXP04050 Expansion Joint 4"X50'

My concrete guy made forms, then poured every other form on day 1. Then on day 2, he removed the forms, put in the expansion joint shown above (or something like it), and poured in the remaining areas.

There isn't alot of concrete over them, just a thin film of 1/16" or so. Over time the thin concrete will just wear off. Rather than leave as is, I was told to grind down the joints and then caulk them so that I had a better more sanitary seal.
 
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Old 09-11-10, 07:12 AM
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The sze of the joint is dependant upon the size and thickness of the slab, but it should be at least 3/8" wide by 5/8" deep, and you should use a backer rod. You want the joint material to have, in cross section, an hourglass shape, with no three sided adhesion. The purpose of the backer rod is to create that shape and prevent the 3 sided adhesion.

Grinding a 1/4x1/4 joint and filling it with sealant is just going to make it harder to repair a year down the road when it fails.
 
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Old 09-11-10, 07:27 PM
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The slab is 6"deep. How deep does the backer rod go down?

Do I use self leveling caulk?

Do you have any advice on brands?
 
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Old 09-13-10, 06:04 AM
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Sonneborne NP1 or SL1 (Self leveling) are both very good, though not cheap. How big are your panels, i.e 10x10, 20x20?
 
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Old 09-21-10, 11:04 AM
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since you've got expansion jnt mtl now, you won't need any backer rod,,, wire brush on a 4" grinder & removeexp jnt to depth rqd by your sealant,,, its IMPORTANT to have CLEAN jnt sidewalls for proper adhesion,,, ck the depth:width ratio of your selected jnt sealant - i like 100% silicone & we used it by the 55gal drum for concrete hgwy jnt sealing,,, np1's good, too.

the purpose of backer rod is to prevent 3-side adhesion thereby destroying mtl cohesion,,, it also allows you to gain the desired shape factor.

easy hands-&-knees work ! Beer 4U2
 
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