# Sealing a foundation gap?



## edta1 (May 20, 2011)

I have a sizable gap between my foundation and my concrete patio. I'm concerned that bugs and water will find its way inside my house. How and what can I use to seal it? I have no idea how deep that gap is either. The gap is about 1" wide and spans the length of the concrete patio (5-6feet I think).


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## Ron6519 (Mar 28, 2007)

Has the gap size remained the same over time or has it gotten bigger? A 1" gap is not usual for that situation.


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## edta1 (May 20, 2011)

Ron6519 said:


> Has the gap size remained the same over time or has it gotten bigger? A 1" gap is not usual for that situation.


I don't know. I just bought the house. I was going to seal it with expandable foam (Great Stuff). That stuff turns hard like a rock though. So if the concrete expands and contracts due to weather (I'm in Chicago), would it hold? How flexible is Great Stuff foam?

We are getting some bug problems. So right now I'm just looking to seal whatever I can.


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## stubborn1 (Oct 24, 2008)

I would pick up some 1" foam backer rod and insert it along the length of the crack depressed about 1/2" from the surface. Use a good self leveling caulk on top of the backer rod for a seal.


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## Ron6519 (Mar 28, 2007)

edta1 said:


> I don't know. I just bought the house. I was going to seal it with expandable foam (Great Stuff). That stuff turns hard like a rock though. So if the concrete expands and contracts due to weather (I'm in Chicago), would it hold? How flexible is Great Stuff foam?
> 
> We are getting some bug problems. So right now I'm just looking to seal whatever I can.


Great Stuff is an inappropriate material for this. As Stubborn suggests, backer rod and a self leveling material. I use a product from the Sika company. There are others. It's sold in home Depot and comes in 2 caulking sizes and 2 colors(tan and gray).
Any mason supply will also carry this product type. 
Key to a good installation is a backer rod size that is tight to both sides or the material will flow past and disappear. 
Sides need to be clean and dry.


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## edta1 (May 20, 2011)

Ok, thanks! do I have to stuff the foam all the way down and try to fill up the gap? Or just filling it at the surface is fine? I have no idea how far down this goes.


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## concretemasonry (Oct 10, 2006)

edta -

I think stubborn1 said to get the apprpriate width for your crack and push it down (it will fit tighly) to allow a required amount of sealer over it. The depth depends on the width of the crack.

The idea is to create an amount of caulk to move and stretch with the seasonal and daily movements of the two concrete elements without letting go or tearing.

Make sure you get the proper caulk and if you a shop for materials by price, you will be doing it again after you have cleaned everything out. Preparation and cleaning of the gap is neceesary and critical.

Dick


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## edta1 (May 20, 2011)

Thanks Concrete,

I understand what stubborn1 is saying, but I guess I should have asked, do I need to fill the gap? If the gap is 6 inches deep, should I keep stuffing it with more and more foam back rod until I get the appropriate depth? 

How should I clean the gap? It's outside. Just spray with water, let it dry for a day, then stuff the gap with foam back?


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## concretemasonry (Oct 10, 2006)

You should not have to fill the bottom of the gap.

For cleaning, a good hose followed by some drying and then a good blowing to get any dust/fines out followed by more drying time, especially if the caulk required a dry substrate for proper adhesion.

Just like painting - preparation is the secret to success.

Dick


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## Ron6519 (Mar 28, 2007)

The point of the backer rod is to limit the amount of material you use and at the same time, get enough material into the crack to seal it.


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## concretemasonry (Oct 10, 2006)

I guess I missed the main point is that you want enough material to stretch between the slabs and not be adhered to the soil below. If the rod is not the appropriate amount for the joint width, it will not work properly.

Dick


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## stadry (Jun 20, 2009)

closed-cell backer rod is used to limit the sealant's depth so it will maintain proper adhesion AND cohesion,,, sika's a good mtl for this whether you use the self-leveling or non-sag types,,, IF you use the non-sag ( ns ), tool ( push down ) w/a teaspoon to force sealant against the clean sides of the joint thus promoting proper adhesion.


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## luckattack (Mar 8, 2011)

Sometimes due to soil conditions, the slab is not tied to the building's footing to allow for extraction and contraction of the soil and movement of the slab and preventing cracking. I would make sure you use some expandable material to allow for it to still move and don't make it rigid.


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## stadry (Jun 20, 2009)

slabs are NEVER tied into structures - be it a building, foundation, or roadway/bridge,,, proper sealant means 1 has picked mtl w/the proper exp/contr qualities IF its installed in the proper depth:width:thickness ratio,,, that's why there are product sheets showing HOW to use it correctly !


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