Oxalic acid and metal roofs

[kighill]

Oxalic acid and corrosion.

I have noticed that damage is being caused to my metal roofs after treatment with oxalic acid. I believe it is the acid which is causing the roof to corrode around the ventilation slots in the roof.

I use Cedar National hives from a well known supplier and the roofs are galvanised, I do not currently own any old equipment, so it is not general wear and tear.

I do not paint the roofs.

I find the damage rather unsightly and I am considering taking the metal off the roof prior to treatment and replacing it once done.

I am considering some sort of plastic tray, such as used for the watering of plant pots etc. Which I can place onto the hive roof and weigh down for simplicity.

Any thoughts or suggestions please.

Thank you

 

[poshpikey]

Solid crown board? Or seal up ventilation on crown board?

 

[kighill]

Thank you, nice and easy solution.
I did have some crown boards covered but not for any specific reason, other than I keep my record cards attached to a piece of plywood, which often covers the hole in my crown boards
This could explain why some roofs were not affected, unfortunately I had not even considered this when noticing damaged roofs.

 

[alanf]

...after treatment with oxalic acid...

How are you treating? Seems unlikely that a dribble of dilute acid in syrup once a year is going to get fumes up to the roof ventilation. If it was the acid, I'd expect a lot more effect on metal runners and nails inside.

More likely just the effect of condensation on the steel edge throughout the year, warm moist air going out through the roof every day. Might be another reason to close the holes at the top if you're not feeding or clearing.

 

[Hawklord]

Galvanizing is only a coating, so if the galv is cut, drilled or scratched it will remove some of the coating. A coat of aluminium paint is usually applied to such areas.

 

[itma]

No such problem with roofs and 3% Oxalic trickling. (And I don't recall any such reports from the vaporisers …)

Open hole crown boards will lead to condensation in the roofspace - and particularly in the colder half of of the year. This shows up as mould/rot of the woodwork, and eventually corrosion of the metalwork - principally from the underside.
This has been noted (and accepted as 'normal') long before anyone started treating bees with Oxalic.

If the environment is damp, you will promote bimetallic corrosion between the galvanised insect guards at the vents and whatever (indoor drawing pins?) is securing them.


80% Acetic acid (used for fumigation) certainly does attack all hive metalwork - eventually even nails are said to fail.

 

[jenkinsbrynmair]

I did have some crown boards covered but not for any specific reason, other than I keep my record cards attached to a piece of plywood, which often covers the hole in my crown boards

The holes in your crown board are there for four reasons:
1) covering with feeder
2) filled with a porter escape
3) fitted with a rhombus escape
4) To be blocked or covered to prevent the passage of air

 

[alanf]

I find the damage rather unsightly and I am considering taking the metal off the roof prior to treatment and replacing it once done.
...
Any thoughts or suggestions please.

If you don't want to cover the crown board holes (I do but plenty don't) and condensation is spreading corrosion, there are some rust treatments from the motor trade. I use Hydrate 80 by Bilt Hamber on classic cars. Any decent motor supplies shop could have something similar and probably in smaller quantities. It converts the rust and leaves a black coating that can be painted, good for halting any developing rust spots before they spread. A few black spots would be less noticeable than spreading rust. Not what you'd want large patches of on a hive when bees are about but small spots dry in 30 minutes; you could replace the lid with a board for a few hours while you treat and return it the same day.