Crack Repair

[CapePizza]

Hello. The outer dome on my WFO has developed a number of cracks on its outer shell. There are no loose bricks on the interior and its just the outer shell where the cracks are visible. If I tap on the shell I can hear in some spots that it's a 'hollow" sound.... . There is no steam coming out of the cracks during use of the oven and the oven holds its heat for a number of days after use. I've read that the cracks can be left as is.... but being that my oven is exposed to the elements I'd rather fill them. Otherwise I can see water getting in there and freezing during winter and making the cracks worse (the oven does NOT have a "house" built around it but does have a large roof over it).
So..... my question.... what is the best "mix" or material to use to fill the cracks? I would plan on taking a chisel to open up the cracks to give the filler material "more purchase"...... Also wondering if adding a fiberglass filler would be advantageous? Any suggestions would be helpful.
As a side note, I did add one of those automotive low pressure relief valves on top of the oven when it was first parged with the perlite mix and final coats.

Other than that.... the oven works great, we use it often.

Thanks for the help!

John

[david s]

If you have a roof over your oven then t will prevent any rain getting in presumably, so the cracks are only cosmetic.

[CapePizza]

Thank you for your thought, David. I'd like to take a more "proactive action". We live in a very moist environment, so during the winter months I can see any moisture that is present in the cracks will freeze causing unwanted results and making the matter worse off. So..... any other thoughts from anyone would be helpful.

Thanks.

John