Fireplaces, Heating Stoves, Flues and Chimneys - repairing my chimney crown

i am repairing my chimney crown and need to know if i need to put a concrete sealer on top after i put on the portland cement???

if i do, can anyone recommend a sealer i can use???

thanks...michael

Originally posted by hobbs_m
i am repairing my chimney crown and need to know if i need to put a concrete sealer on top after i put on the portland cement???

if i do, can anyone recommend a sealer i can use???

thanks...michael If you put a good pitch on this chimney crown and have about a 2" overhang all around it.
You used a rich sand and cement mix, Id say its ok. ED;)

what do you mean leave a 2" overhang??? and how much pitch???

thanks...michael

Ed, The top course of brick should overhang the rest of the chimney by 2". On the top surface of the chimney, mortar should be placed at 2 on 1 pitch (in that range) between the chimney capo and the edge. The pitch will direct water to the edge and the overhang will cause the water to drip at this edge instead of running down the sides of the chimney.

The crown is the sloped masonry at the top of the chimney. A very common problem with the crown is that it is formed from mortar. The mason places mortar on top of the last course of bricks and slopes it away from the flue. The mortar shrinks and cracks. Then gaps form between the crown and the flue. The cracks and gaps provide easy access for water to saturate the chimney.
The nature of a chimney is such that the flue liner gets warmer than the outer bricks and chimney crown. The flue will expand at a greater rate than the masonry surrounding it, so it's necessary to leave an air space between it and the crown. To prevent water from entering this air space, flexible sealant is installed between the flue and crown. The crown must also be protected with flashing. The flashing is installed so that it wraps from inside the flue, over the flue edge, behind the crown and out the bottom of the crown. Any moisture that makes it past the sealed opening is diverted outside the chimney by the flashing.
For more information on chimney crown construction, get these two Engineering & Research Digest pamphlets from the Brick Industry Association, 11490 Commerce Park Dr., Reston, VA 20191. The postpaid cost for the pair is $1. They are: "Proper Chimney Crowns," No. 628, and "Flashing Chimneys," No. 635.

Becker, N. Chimney Crown Leakage. Homeowner's Clinic. Retrived 04 October 2002. http://popularmechanics.com/popmech/homei/9909HIHOM.html

There is a photo of a proper chimney crown at the above link.

The chimney crown (also referred to as the chimney wash) is the top element of a masonry chimney. It covers and seals the top of the chimney from the flue liner(s) to the chimney edge. A proper chimney crown should be made of a portland-cement based mixture, not common mortar mix since the mortar mix is not designed to withstand weather abuse. The crown should be cast or formed with a downward slope with an overhang or drip edge that projects beyond all sides of the chimney by at least two inches to keep water runoff away from the chimney masonry.

Most masonry material is porous and will absorb large amounts of water. Common brick is like a sponge that absorbs water and wicks it to the chimney interior. Defective mortar joints or poor quality mortar or brick can increase this tendency. There are several waterproofing products on the market designed specifically for masonry chimneys. Look for one that is vapor permeable so that the chimney can release built up moisture from exhaust, but no external water will get in. If the chimney is already damaged or dirty, it should be repaired and cleaned before it is waterproofed.

Chimney caps are probably the most inexpensive preventive measure to prevent water penetration and damage to the chimney. An uncapped chimney can collect rain water and funnel it directly to the chimney interior. Moisture in a chimney flue can contribute to liner deterioration, interfere with draft and create potential for blockages. Caps also will keep birds and animals out of the chimney and can prevent sparks from landing on the roof or other combustible materials if there is a chimney fire. Caps should last a long time if they are made of sturdy, durable and corrosion-resistant material. A full-size chimney cap may be a bit more expensive, but it will cover the entire chimney crown and protect it from wear.

Chimneys Can Be Safe And Last A Lifetime With Annual Cleaning And Inspections. contractor.com. Retrieved 04 October 2002. http://www.contractors.com/homeowners/resources/homecare/chimneycleaning.html

You got a lot of help here on your chimney and all good before i got back to you.But ill tell you what, I have had to build a lot of metal chimney tops and clamp them to the tile to help keep out the water and keep the water off the top of the chimney.So you might look into this also ED ;)

looks like a project I will have to take on in the future; my chimney crown is chipped and cracked; cement pieces are falling off.

we also have premade crowns; drop it in place and seal it- anyone with experience on those?

Tell me more about the premade Chimney crowns???

I wish I could tell you something about preformed crowns; I have been putting off that project forever. I been up there few month ago to replace an outdoor antenna and noticed how bad it is getting- I tried not to disturb it.
the chimney still standing!
I honestly have not seen the premade crowns- only heard about them.
when I get around to doing this project, since I have worked with cement before- tiling- i think I will just mix my own mortar- cement sand etc. more work but I would think less cost.(two chimmneys. )