I’m off to work now, but can take photos later. If there is a leak it would have to be inside somewhere because the brood box sits well on the base and the base sits well on the tabletop.
Good to know, but I just wanted to let you know that we want to help if we can. 
I found on my screen when it arrived that the wires were not straight even spacing causing some " holes" to be quite large maybe big enough for a bee. So I straightened/ aligned all the wires by hand before using it. So all the holes were an even size.it might be that maybe, good luck Mathew. Cheers Tim
Hi Tim - that may be the problem - I’ll have a real good look when I take the box off the base - it’s a nuc getting established so I’m a bit nervous about upsetting them, but need to know what’s going on here.
Thanks for your help.
Matt
Well Tim you were right - some of the mesh was out of alignment - and watching the bees trying to get through there doesn’t seem to be much room for error - I’m certain they were getting through some of these bigger spaces.
I ligned the mesh up as best I could and put the hive back - sealing up the access to underneath once again - I’ll come back again, maybe at night and see if that did the trick. A more sturdy mesh would be much better for anyone making this up from scratch - don’t particularly like this mesh, but I guess it was economical for mass production.
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I hope that fixes the problem Mathew, I agree about the wire mesh, I think it would be a lot better if the wires were sort of “welded” together so the individual wires couldn’t move. Cheers Tim
Hi Matthew, I work about 60 hives in Buderim on the Sunshine Coast. I’m successful with solid floors. I wouldn’t consider SBB’s. You could use the core flute as a solid floor & solve your current problems.
Thanks Jeff - I do understand that the screen floor is not necessary but it seems to me that it would make a good beetle trap system.
Hi Dawn I bought metric stainless steel mesh with nominal 3mm apertures. The occasional bee gets through but it’s a very rare event. I’ve seen the #8 hardware cloth and its apertures are much smaller than 3mm. It runs 8 wires to the inch so although the repeat distance is almost 3.2mm, that distance includes one wire diameter. If the gauge of the wire is approximately 0.5mm, then the aperture space is actually 3.7mm or thereabouts.
Well, you are very well-informed! However, there is quite a lot of info on hardware cloth, and what sizes bees of various types can get through. Size #8 is universally considered bee-proof, although I completely accept what you say. There is a very nice summary of the various sizes of mesh, and what to use them for regarding beekeeping here:
I would be negligent if I didn’t use Michael Bush’s summary too:
http://www.bushfarms.com/beeshardwarecloth.htm
Unfortunately, they are all US measures, but you will get an idea at least.
Best,
Dawn
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Very nicely done in your detective work. It is wonderful to see people who care so much about their bees. I know this took a lot of effort, but many others of us are learning from your hard work, so thank you.
Dawn
Dawn, 10 minutes on the internet and anyone can be instantly ignorant. When I was sourcing my screen I spent uncounted hours attempting to find the exact best mesh to use. In the end I chose the largest aperture I could together with a wire diameter strong enough last as long as the bottom boards.
Bees can fit through as I discovered today but mostly they don’t seem to bother.
I was making up something called a Swarthmore box with a whole lot of shook bees and a couple of good frames of honey, nectar and pollen. The box needs to be sealed but ventilated, so bees can breathe but not escape. I noticed a few had wriggled their way down through the 3mm mesh. They didn’t get very far because the base is fully closed with fly screen.
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Sciencemaster - I do appreciate your research - I’ve been following you and your research/construction - good stuff!
A few bees have gotten through my realigned mesh but I cut up a wastepaper basket that was made of a black steel mesh of about 3mm and used it to cover the diatomaceous earth - now, even if a few bees get through the base screen they won’t get through the waste basket mesh, and I’ve already caught a bunch of beetles in the dust!
So I’m satisfied that I have a system now that works - if I want to further limit the airflow under the hive in winter I’ll just use tape to close off the entrance (at the moment it’s a steel strip with holes in it that doubles as a tray handle that not only seals the entrance to the base but I can grab to pull the tray out).
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Thanks Matthew. For the third major iteration of the screened bottom board I simplified the bee entry and added a syrup feeder at the back. I made 6 of them to go with a set of five frame nuc boxes. The design is slowly getting towards something useful but I suspect it will always be a somewhat complicated bit of kit.
I started out with a screened board and its a good way to help keep the hive clean. I will try the tablecloth idea when I check the hive this weekend.
Hi Matthew,
Since your post, my Flow hive has arrived, and I now realize that I was wrong. Although the Bee Thinking SBBs have #8 hardware cloth, the Flow SBBs use #6. There is a discussion about it here, along with some photos I took of my Flow SBB next to a Bee Thinking SBB:
I think I am going to dismantle the Flow SBB and change to #8 mesh, because I really don’t want my bees going through that screen.
Dawn
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Thanks for letting me know Dawn.
Matt
Couldn’t you just install a finer mesh over the existing? Do you need to dismantle it?
Yes, I need to dismantle it. The issue is mathematics and geometry. If I lay something that is divided into eighths over the top of something that is divided into sixths, some of the gaps will only be 1 or 2 mm. Nothing will be larger than just over 3mm, but a lot of the screen will be too fine. It offends my OCD not to have it all as a known quantity - that is my problem, not yours, just the way I am made.
I walked at 12 months and was fully potty-trained at 18 months - TMI (too much info), I know, but perhaps you can see why I have to take it apart… 
No that actually makes perfect sense.
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