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kboorman 03-08-2008 09:53 AM

Sealing pipe through block foundation
First post, so be gentle. :)
I have to run a 1/2" galvanized pipe (gas) above grade through my cinder block foundation and need to seal it. Would silicone do or would hydraulic cement be more appropriate? I wasn't sure if the thickness of the block would give the cement enough surface to really adhere to. If I use the cement, how big a hole should I drill to create the proper gap from the pipe to the block? Thanks in advance. Kirk.

terri_and_jj 03-08-2008 10:45 AM

Just get some foam in a can. the stuff works great, but there are a few things to keep in mind.

a. the regular stuff really expands as it cures, so use it sparingly or you'll end up with a big mess. i've seen people buckle windows and blow a hole in drywall with spray foam.

b. this stuff cures with air, so if you try to use too much it will never fully cure in the middle. the rule of thumb is if you make a glob bigger than your fist, the center won't cure. so this means do it in stages if you are filling a large void. you might need a couple cans, because once you crack a can, even if you don't use the whole thong it sometimes cures in the nozzle. i use the big cans with the screw on gun, so i really don't remember if you can use half a straw can today, and the other half tomorrow.

c. cure time is much faster in warm weather than cold, so make sure you give each application ample time to cure based on the temps you are dealing with

once it cures you can trim it with a knife, sand it, and even paint it . painting will give it some UV protection on the exterior side, and make it last longer. you can also buy it in black, but not sure if the local Depot or Ace hardware will have black foam on the shelf

kboorman 03-08-2008 10:48 AM

Is the expanding foam waterproof?
I thought about using that stuff, but it seemed to be a less durable solution.

terri_and_jj 03-08-2008 10:54 AM

i can't remember the exact spec, but i remember hearing or reading that it's not technically waterproof, but it will hold back flowing water, something like that.

what you could do, if you are really worried about it, is use expanding foam to fill the large portion of the void, that patch the last couple inches around the pipe with cement

Bondo 03-08-2008 11:00 AM


1/2" pipe measures about 3/4"OD,.....

Punch a 1" hole thru, insert the pipe,+ pack Hyd. Grout into it.....

It'll last darn near Forever....

AtlanticWBConst. 03-08-2008 12:15 PM

Vote: Grout or cement the gaps/spaces.
Once cured, go back and seal the materials where they meet together with a good NP1 caulk (polyurethane based caulking).

kboorman 03-08-2008 05:26 PM


Originally Posted by Bondo (Post 105520)
It'll last darn near Forever....

Thanks for the responses guys, that's pretty much what I'm after. I don't like doing things twice so I don't mind the time to do it right the first time. Hydraulic cement it is.
Only problem I have is my biggest bit is 3/4" and I don't feel like buying another right now. I guess I could drill through and carefully chisel it out to 1" or so?

js2743 03-08-2008 10:42 PM

if you have a 3/4 then why would you want to make it 1" for when you only need 3/4 then you have no hole to fix.

kboorman 03-09-2008 09:45 AM

I figure a hole the exact size of the pipe won't allow me to get the cement (or anything else) in there to seal it. I'll probably taper the hole outward on each side of the block so I can get a little more bonding surface as well.

AtlanticWBConst. 03-09-2008 11:04 AM

Originally, I had thought (assumed) that the pipe and the hole were bigger.

Use a polyurethane sealant. You need to seal the concrete from weather erosion.

Bondo 03-09-2008 02:06 PM


If it's that Tight a fit,.... Just caulk it....

kboorman 03-10-2008 06:46 AM

Thanks again guys. The pipe wouldn't go through the 3/4" hole (I guess I could've hammered it through though), so I enlarged it a bit. The way it stands now, the hydraulic cement should be fine to seal it but you think that needs to be protected from erosion?

AtlanticWBConst. 03-10-2008 06:54 AM


Originally Posted by kboorman (Post 106053)
.....the hydraulic cement should be fine to seal it but you think that needs to be protected from erosion?


FWIW: It's something I know can happen (When the area is directly exposed to the weather and rain) I have seen it happen, while doing construction evaluation inspections.

The grout or cement is fine on larger gap areas, but the point where the two materials meet should be caulked.

Since you don't have a larger gap, just use the polyurethane caulk.

kboorman 03-10-2008 08:52 AM

Thanks, Kirk.

majakdragon 03-10-2008 09:38 AM

I would use a silicone caulk. The concrete will move or the pipe will expand and contract from changing temperatures. This could rub a hole in the pipe. Not fun to get a gas leak inside a concrete block. Silicone will allow for movement.
Sidenote: This is another one of those instances where the Code is different. Most areas require black iron pipe for gaslines since the galvanized coating can flake inside the pipe and clog burner orfices. Florida was the first place I saw galvanized used on gas services. In Ohio, it was not permitted.

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