Securing the chimney top plate

[JimmyMood]

I installed a woodstove insert in December with a full length liner. I glued the top plate to my 13x13" chimney flue using high-temperature silicone, which seemed a bit marginal to me considering wind pressure and the expansion rate of steel, but the dealer said it should work. This morning on my way to work I looked up at the chimney and observed that the top plate looks like it has detached and is slid to one side of the chimney.

I have a few thoughts about securing the top plate better, but how have other people here done it?

 

[Hogwildz]

I installed a woodstove insert in December with a full length liner. I glued the top plate to my 13x13" chimney flue using high-temperature silicone, which seemed a bit marginal to me considering wind pressure and the expansion rate of steel, but the dealer said it should work. This morning on my way to work I looked up at the chimney and observed that the top plate looks like it has detached and is slid to one side of the chimney.

I have a few thoughts about securing the top plate better, but how have other people here done it?

If it has side flanges the fold down over the sides of the old clay liner, you can drill a couple holes each side. Then install some pointed end bolts. Just be careful not to tighten them too hard and crack the clay tile. Most chimney pipe dealers sell these bots, &/or supply them with the piping kit.

 

[Hubjeep]

Mine is held on with only silicone, the manufacturer of the liner kit said that is how they do it. I am not too worried, the worst scenario is that it shifts to one side allowing some cold or rain/snow down the chimney.

 

[DriftWood]

ORBITER THERMAL PROTECTION SYSTEM

“To prevent damage to the tiles, Strain Isolation Pads - a layer of nylon felt Nomex (flame-retardant material)- are used between the tiles and the orbiter’s surface. The pads are bonded to the tiles, as well as to the skin of the Shuttle, with RTV, a room-temperature vulcanizing silicone adhesive.”

“All of the major ingredients in the Shuttle’s external Thermal Protection System-tiles, Flexible Insulation Blankets and Felt Reusable Surface Insulation-are bonded to the orbiter with the RTV adhesive. The cement will withstand temperatures as high as 550 degrees F, and as low as minus 250 degrees F without losing its bond strength.”

(broken link removed)

That said this is not rocket science.

Silicone needs a clean surface to stick to. Chances are the area at the loose spot was dirty when you put it down. Cleaning with brushes, soap and water is not enough. A fast evaporating solvent should also be use to clean to remove any oils. I like alcohol or acetone depending on the surface and plain white paper towels.

 

[JimmyMood]

I cleaned the terra-cotta with a wire brush and the SS plate with the same brush and alcohol. I haven't yet climbed up to the roof to see what the adhesive separated from, the plate or the chimney, but I would guess it was the metal plate. One thought I had, is that I probably pressed down on the plate too much and squeezed out too much silicone. There was some trouble keeping the plate centered while the adhesive set, so I put some weight on top till the adhesive set. I think I'll leave a bead of about 1/8" to enhance the flexibility of the bond, and find another way to center the plate while the silicone sets. Now if I remember right, I need to clean off all the silicone because silicone doesn't stick to itself very well right? That should be fun.

 

[pulldownclaw]

I had the same issue with mine. I've got the same 13x13 clay top, and when I went to secure my liner and top plate to it the liner was pushing it to one side, so the top plate wouldn't sit on it straight. I ended up drilling pilot holes and screwing some tapcon screws down through the top of it, and also put silicon around it. I was worried about cracking the tile, but I took my time and made sure I was centered up on it and it went well. Good luck.

 

[RedRanger]

Mine is motared to the clay liner. It ain`t gonna move until we break the mortar to install another one. Hopefully many,many years from now.

 

[swestall]

While I am not sure of the spelling, Home Depot carries an adhesive (Sika or Sikka or something like that) that bonds rock, etc to metal or just about anything else. I used this on my top plates and many other items around the house, it will only come off by peeling the item off and scraping the residual from the masonary surface. At my local store it is carried in the Building materials isle by the concrete supplies. This is a no fail item.

This is good info for everyone....

 

[begreen]

My cap was put on cleaned bricks with GE Silicone II, thickly slathered over the full width of the top bricks. It was a temp installation until I could take down the chimney. I was surprised when I removed it 5 years later that it was still glued on really tight. I pulled the cement out of the joints and had to chisel off the cap with a long stiff putty knife.

 

[Stihl025]

My 8" terra-cotta flue extends out of the brick about 1.5 inches. I think I am going to try to cut and bend the top plate down next to it and secure it with a couple stainless steel hose clamps piggy-backed together. It might take some cutting and bending of the top plate to make a tight fit, but the clamps would be secure and easy enough to remove in case of emergency.

 

[crazy_dan]

Since nobody else said it J.B. weld.
I actually like the hose clamp idea so I would give that a try and you could always put some silicone in between the sides and the cap before you screw down the hose clamps.

 

[jtp10181]

We do them all with just silicone. Every once and a while one will let go but I would say the failure rate is 1% or less.

 

[DriftWood]

Could be the metal has a release coating or oil on it. Clean the top plate mounting surface with a solvent also.