Once sealed there is not enough of an air exchange in the hive to release moisture which then becomes condensation. Not good if there is too much in Winter.
Really the bees didn't begin doing this till this past Fall. Yet each week i had to scrape the propolis off all the HTF vents on all the hives. It made the chore of refilling the HTF's take forever. After the end of last Fall i looked into HTF's online. I found where others had used the #8 mesh to close off the feeders instead of the plastic dividers my HTF's had.
#8 mesh is the same mesh used in Screened Bottom Boards. I've never seen a bee propolis up one of those. So i figure it should work well on my feeders. It was easy to do. Just pull off the plastic divider, trace it's outline on a sheet of mesh then cut out with tin shears. The top bend is made by rolling the mesh against the plastic divider. I used 3 - #14 x 1 inch sheet metal screws. They do not make a tight fit but it's snug enough.
|Old Plastic & New Mesh Dividers|
Another good thing about the mesh is it will add foot holds for the bees. The plastic dividers are smooth and the occasional bee would drown. The mesh will seem like ladders to the bees so fewer bees should die. The mesh is pliable so I'll need to watch how i handle & store them in the off season. Overall these should make the HTF's even better.
The first two mesh dividers worked perfectly. In 2011 two more were made that didn't fit well and let bees escape into the HTF. All four of these used a design that was flat and stopped at the edge. To fix the escaping bee issue new mesh was formed like a bucket that folded back at the edges. This blocks any gaps that may occur when cutting to size. Plus the mesh overlaps on ALL sides.
|This flat design led to bees trapped in the HTF|
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|This bucket design keeps the bees were they belong|