Went for a stroll on my roof a few days ago, cleaning gutters, etc.
30+/- yo, brick chimney, 2 tile flues (fireplace and oil heater), mortar cap on top of bricks to shed rain water.
Found a bunch of cracks, missing mortar, etc. in the mortar cap – this did not look good, as the missing mortar exposed some of the “cores” in the bricks, allowing water to collect and ultimately freeze this winter. Potentially blowing the sides off of the bricks.
I chipped back the mortar around the edges of the worst areas and re-mortared just with some Quickcrete mortar mix to get through the winter.
In the spring, I plan to completely remove the old mortar cap (and the patches) and replace the entire mortar cap.
Is there any “special” mortar mix or different proportion of sand / cement / mortar mix I should be using for this application?
Thanks!
Jim
Replies
You shouldn't use mortar at all. The only system I've seen that's fairly long lasting is a pre-cast or poured in place concrete crown. Some water still gets through, though, and the joint between the flue tile and concrete is suspect. The best solution is a full chimney cover which keeps water and varmints out of the flue as well as water off of the chimney top.
I found this detail and I like the flashing at the top:
View Image
copper p0rn
Thanks for the drawing!
Will have to be poured in place as there are 2 individual flues coming up the brick chimney.
13x13 tile for fireplace, 9x13 for oil furnace. Unfortunately the original mason did not pay too much attention to alignment. The 13" tile is offset by about 2" from the 9x13, i.e, one side of the 13"x13" should form a straight line with the 9" side of the 9x13. Instead the 9x13 lies about 2" west of the line.
I'm sure a precast is not available for that scenario.....
Jim
JimNever underestimate the value of a sharp pencil or good light.
That is a very good drawing on how to install a chimney cap. Be sure to follow all of the steps. The flashing under the cap is important for several reasons. Among them, is that is isolates the concrete cap from the brick.
You can make a form out of 2 x 4's and pipe clamp it to the brick. Be sure to leave the space around the flues. You can wrap the flues with cardboard or something like that where you want the space and then pull it out when the concrete cap hardens.
Make sure the backer rod is deep. (at least an inch) This allows you to get a good amount of caulk in there. Silicone seems to work well. I've never had to go back and redo one of these where we used a big slug of silicone.
Use rich concrete...at least a 6 or 7 bag mix....and use mesh or #3 rebar to reinforce the concrete. You can coat with Thoroseal or some product like that for extra protection. If you use a clear sealer, be very careful with it because most of them will dissolve a roof shingle instantly if you drip onto it.
More great information!
I was good with the flashing, forming, flue wrapping for a space, mesh / #3 rebar, caulk, sealer..........but,......not a mason - cud' ya tell from the original question?........
you lost me a bit - Wassa' "6 or 7 bag mix"?
On topic of mix - for aggregate, is pea gravel OK or should I be using something bigger / different.
JimNever underestimate the value of a sharp pencil or good light.
A six bag mix means using 6 bags ( 6 cu. ft ) of cement per yard of concrete. That is a common mix that we use everyday for driveways and sidewalks. A yard of concrete is 27 cu. ft. So to convert that ratio to something practical for small batches, you would have for instance...6 or 7 shovels of cement to 20 or so shovels of the other ingredients which in your case would be pea gravel and mason sand and water. The batch plant weighs these ingedients when mixing, but for a chimney cap, I think you can come close enough with the shovel !
I wouldn't use anything larger than pea gravel for a chimney cap. Make sure you tap or vibrate the sides of the form to work the voids out of the outer edge of the cap so you have a nice smooth edge.
Thanks again!
I can work with that formula! Printed and filed for the spring.
I figured it had how much portland was in the mix.
Still not a mason.
Jim Never underestimate the value of a sharp pencil or good light.
For that small a job, we usually use Quikrete concrete mix and add portland cement to their mix to get a rich concrete. I like their mix of small stone and sand for small projects like yours.
Do not !!! I repeat, Do Not !!! Use their mix right out of the bag. No matter how they have it labeled, there is not enough cement in those bags to produce a strong concrete that is water resistant.
Adding a good, big shovel full of portland to one of their bags usually does the trick. Watch when you are mixing it. It should be real sticky when you have enough cement in the mix. Higher cement content makes for a much more water resistant concrete cap.
Be sure you don't water the mix down too much. It should be sticky and slightly loose, but not at all runny.
Uhhh... Quickcrete is available in a 5000# mix. Just make sure you follow the proportions of water to mix. More than adequate for the chimney cap.
Life is Good
I'm sure that would work for a chimney cap. Trouble is, you can't even buy that around here. I get a kick out of their labeling "commercial grade" concrete mix. That means they actually put some cement in with the stone and sand!
The typical Quikrete for sale in most places is almost a joke as far as concrete goes. It has so little cement in it that it doesn't hold up to anything.
Adding your own cement to their mix until it looks and acts like normal concrete is a better way to go in my opinion, and certainly cheaper.
He would be very disappointed in the results of his hard work if he just mixed up some Quikrete straight from the bag.
You can even get fancy and use 5" Ogee K gutter face for your form. Looks like a crown moulded chimney cap then.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
PROUD MEMBER OF THE " I ROCKED WITH REZ" CLUB
I like that idea!! What exactly, is gutter face?
Just cut off the show side of some old K gutter. The face.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
PROUD MEMBER OF THE " I ROCKED WITH REZ" CLUB
Now I got it!
Yeah, ya just line the form box.You could always use wood crown too but it would be reversed from what you normally see, the gutter lets you use the "back side" to reproduce the "face" profile. wood is flat on the back so you can't copy it exactly.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
PROUD MEMBER OF THE " I ROCKED WITH REZ" CLUB
Hey. That through flashing under the cap. How do you adhere that to the flue?
5" sill seal works great for wrapping the flue before pouring the cap. Nice deep seperation that way.
That through flashing under the cap. How do you adhere that to the flue?
Silicone works just fine. Usually it's not that hot up there. If it is, you can use the hi-temp stuff. I'm not sure what effect that stinky silicone ( the old stuff ) has on copper flashing. That has me wondering?
I haven't see any adverse reaction to copper from the acetic acid silicone, but as rule, we've ( me and seeyou) have been using Geocel tripolymer exclusively.IIRC I heard some where, that the Brushable form or geocel was developed just for repairing chimney washes ( the failing Crete).
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
PROUD MEMBER OF THE " I ROCKED WITH REZ" CLUB
I'll check that out. I see Tom Silva using that all the time.
BTW, I like your new logo!
the backer rod is a good choice for pouring the cap...
i've also wrapped braided rope around the flue and then pulled it out the next day ...
this gives room for a caulk joint and allows some movement of the flue independent of the capMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Yeah, check out Seeyou's diagram closely and you will be all set.
The two key design features-
1 Overhanging the brick. That's the whole point after all, to
shed the water.
2 backer rod (or some sort of clearance for expansion) around the flues.
That is the most common failure point.
Pour it in place, let it cure and keep the joint around the flues
caulked.