taping plaster joins

[maxpower]

Hi there, As a matter of interest - the practice of taping plaster joins was raised by a mate who didnt bother and just ran cornice adhesive into the join, which was what was on hand.
The thinking being the plaster compound sets hard so why put flexible tape down? If anything moves the plaster will surely crack before the tape is affected. Seems to make sense in theory.

[OBBob]

No I think the tape provides a reinforcing layer to stop the plaster cracking in the first place. Same theory as reo in concrete.

I guess the best argument for your mate would be that it is a tried and true method used for many years ... if the tap wasn't required I'm sure plasterers would happily leave it out!

[Bluegum]

Yep I thought that as well. The whole idea was for the tape to reinforce the joint. I reckon rod@plasterblock (think thats his forum name) may hold the answers to this one for us all.

[maxpower]

Hi- thats what we tried to work out - how can a flexible piece of tape stop a ridgid piece of plaster cracking...if the tape was steel it would help make more sense. As for reo in concrete - tape in plaster would be like burying carpet in concrete.....dunno if the practice is more historical than anything. Any ermmm concrete answers ...???

[duckman]

Hi- thats what we tried to work out - how can a flexible piece of tape stop a ridgid piece of plaster cracking...if the tape was steel it would help make more sense. As for reo in concrete - tape in plaster would be like burying carpet in concrete.....dunno if the practice is more historical than anything. Any ermmm concrete answers ...???

The tape is most definitely required as reinforcement. As for the perceived rigidity of steel reo, pick up one end of a full sheet and see how much flex is in it.:D

Making structures too rigid actually weakens them. A degree of flexibility is required.

[maxpower]

Hmmmm .... so mebbe the tape helps make it more flexible so it wont crack ... i reckon if it sandwich a sheet of plaster between two sheets of cardboard its a helluva lot more flexible ... oh its already been invented -thats called Gyprock... Eureka thats prolly the point - flexibility. Cheers

[duckman]

Hmmmm .... so mebbe the tape helps make it more flexible so it wont crack ... i reckon if it sandwich a sheet of plaster between two sheets of cardboard its a helluva lot more flexible ... oh its already been invented -thats called Gyprock... Eureka thats prolly the point - flexibility. Cheers

Well, no reo will stop either plaster or concrete from cracking. The reo keeps the number of cracks to a minimum and helps stops the parts from moving apart thus keeping the size of the cracks to a minimum.

And you're right about the Gyprock sheets themselves, they are quite flexible, so much so that they can be bent into quite small radius curves without any kerfing or even dampening of the sheet with water and without the faces cracking. :)

Cheers,

Mark.

[rod@plasterbrok]

Lol I have seen a plastering job done with out using tape.

It wasn't a pretty sight!!!

The old fibrous plaster sheets were joined without tape. But the joins were either scrimed with hemp from the face or the back of the joint.

More commonly face scrimmed. The scrim acted the same way as the tape.

Like any thin coating of brittle material it needs reinforcing or it will crack at its weakest point. The tape acts as a continuation of the paper liner of the plasterboard sheet.

It is still weaker than the sheet itself as it is only on 1 face, that is why back blocking is recomended for plasterboard ceiling joints.

By the way I feel a bit redunant here at the moment. No one has any plastering problems it seems. I don't know a thing about painting lol.

Interesting topic!!

Cheers Rod Dyson