Regarding rims on the shield, this picture shows some edge clamps from Birka shields.
Look at 5b, the description say it is a wood core faced with leather on both sides, and a leather rim under the metal clamp.

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Interesting topic! In regards to:

Kristjan Runarsson wrote:

The grave shields from Gokstad in Norway had rim holes but they may also have been built specially for the burial because their plankswere painted. Thus they cannot have had a facing since if they had one the decor would have been painted onto the facing and not the wood planks.Therefore these shields cannot be considered representative of combat shields. There is evidence of leather shield facing from Birka and from Anglo-Saxon Britain...

I should mention that there was an article written, from Sweden I believe, that mentioned animal 'gut' being used to face a shield find. This might not have been in a viking context, but I think it was - I will try to find it to reference here.
There was some confusion with the translation as to whether it was stomach or intestine being referred to, but in either case those materials are usually very thin and - depending on preparation - almost completely transparent.

This means that a shield may have been painted or otherwise decorated directly onto the wood, yet still have the advantages that a thin facing offers, as discussed in this thread.

I have not seen anyone use 'gut' on a shield in this way in a modern context, but if anyone knows of an example, please post it!

Sounds like I just gave myself a new project... ;)

Very interesting read. I'm also thinking about constructung a viking style shiled of my own, and it's really hard to find reliable information. I have some questions that I couldn't find answers to, so I guess I might as well ask them here.

We see in a lot of depictions longships, with a row of shields hung on the outside, and archeological finds seem to support the idea that shields used to be hung on the outsides of ships. This suggests to me, that the shields were somehow made waterproof. How would you achieve this with period materials?

The planks can be glued together with casein glue, which is water resistant, and the iron bits will last quite a while before rusting away, so the basic construction is not really a problem. Casein glue doesn't stick well to anything other than wood though, so the rawhide facing must have been glued on with some kind of hide glue or fish glue I suppose, which is not water resistant at all. (maybe pine sap?) Rawhide itself would stand up to a little bit of rain, but it soaks through fairly fast. Paint or gesso as suggested in the previous post is as water resistant as the binder used, which is probably not very much. A liberal amount of grease on top of it all would pretty much solve the issue, but then you wouldn't really want to wear the shield slung over your shoulder I guess, so it doesn't stain your clothing. Any ideas?

The other question I have is about the bosses. I've read and heard in several places, that the surviving historical bosses were a lot thinner than what's commonly used for reenactment shield bosses, but I can't find any actual measurements. The reenactment boss I bought is 2mm mild steel, and I don't think I could put much of a dent in it with a sword or a spear, maybe a bit of a dent with an axe, but some historical bosses show quite extensive battle damage right through the ages. Anyone knows where I could find accurate data about the actual viking era finds?

A shield is going to get soaked in water regardless of whether it is outside or inside the ship.

Casein glue isn't waterproof; it is water resistant and salt lowers that resistance even more.

Well, yes, that was kind of my point, it seems extremely impractical to keep your shields from getting wet on a sea voyage in an open ship, or on the march if it's raining. It also seems quite improbable to have shiploads of norwegian vikings disembark in Ireland only to find out they are unable to fight the local militia that scrambles to meet them, because their shields fell apart on the way. Both Scandinavia and Britain see a fair share of rain throughout the year, so in my fairly strong opinion, there had to be a way to make these shields to some degree waterproof.

Why? Instead of relying on glue, all you need is some nails - just like the ship itself. In the ship's case, the wood needs to be wet so that it can swell and tighten the joints. This swelling might prove beneficial for shields too. Keep in mind that a shield was only meant to last for a few seasons and to be repaired after every encounter. Re-enactors tend to over-build everything because they don't want the hassle and expense of routine maintenance and regular replacement of their kit.

Because nails other than the ones holding the boss/handle are just not really present in any period finds as far as I know.

Metal nails where expensive, not outlandishly so but shield finds only have a dozen nails or so.
Shields where semi disposable, duels give people three shields so clearly there not expecting one to last.

And that's in single melee combat, in a battle with arrows and javelins flying you might have all sorts of damage.

I am not an expert on European plank shields, but they appear at hundreds of sites across more than a thousand years and I do not know any which had traces of nails joining the plans to one another, and usually the nails survive better than the board.

M., I would write to people and groups like Hurstwic and Roland Warzecha and ask for a reading list on Viking shields.

And here is a post by Roland Warzecha with specifications for one 8th century boss from Saxony https://www.patreon.com/posts/thickness-of-22696471

Getting real information requires either borrowing a lot of technical archaeological reports in different languages, or talking to people like Roland who visit museum back rooms and measure finds.

I'm just thinking here but surely nails have a risk of spitting the wood and with the thinner wood by the edges even more so.

Thanks Sean, that's a very interesting link. I'm not a historian or archeologist, so I unfortunately do't have the connections to get access to archeological records, so it was very useful.