A couple of questions for a plaster expert!

[andynumpty]

Hi, I've done a bit of plastering in the past but seem to have a couple of questions.

What's the best way to stop the jointing scrim from showing through the finished plaster. Even after two coats sometimes you can see the mesh or even a raised ridge along the join.

Also sometimes i've had the second coat not adhere to the first & when polishing up it seems to just come away.

Am I doing something thing wrong.

Thanks in advance.

 

[stevethespreader]

1.put the plaster on thicker to stop the scrim grinning through you must be putting 2 thin coats on, putting it on thin is common amongst the inexperienced
2. if the second coat has not adhered to the first you may have let the first coat dry out to much before applying the second coat which would cause the second coat not to stick

 

[roughcaster]

I've seen many a finished plastered wall with the joint scrim tape showing through, and the un-even plasterboard joins showing too. Both look terrible, and it's because of the plaster being put on too thin. People might say, "well i did put on two coats", but if you just consider how thin the tape itself is, and then think,, you've just covered it with two coats of multi finish, but you can still see it,,, it's obvious the overall thickness is far to thin. I never skim plasterboard with just multi finish, and never will. I put on two coats of Bonding coat first. It takes twice as long to plaster a room that way, and costs more to do, but i defy anyone to spot the tapes, plus, using the bonding, it's not a problem covering over a bad joint that might be mis-shapen, or plastering over a wall that's had a badly boarded door opening, filled in. In short, it's thicker coats of plaster overall,, it's float and set onto plasterboard, and as i said, i always do it that way, whether onto new boards,, or onto old painted boards.
As regards to the second coat not adhering to the first when polishing up, i know what you mean, and it can happen when you overpolish with a dry trowel, it can take the finished polished surface off in small areas, and the more you try to sort it, the worse it gets. Not a good idea to overpolish anyway.

 

[1john]

loving the idea of the bonding coat over the entire plasterboard, i did use it to try and feather out some bad joins in some badly bowed boards on a chimney breast (my own fault), but in hindsight i could have ran some straight edges up either side and bonded the lot up.

 

[roughcaster]

This is one thin coat of Bonding coat plaster, put over a thick hessian jute scrim,,, you can hardly see the scrim through it. By the time it got another coat, plus two coats of multi finish, it's "literally impossible" to see it, no matter what joint it's covering,, plus the bonding coat allows you to blend away any badly shaped boarded areas, using a thicker/thinner coat as required.
To be able to see a thin joint tape through 2 coats of multi finish, is un-believable really, but i know it happens.

Untitled

• roughcaster
• 6 Oct 2008
• 4

 

[roughcaster]

loving the idea of the bonding coat over the entire plasterboard, i did use it to try and feather out some bad joins in some badly bowed boards on a chimney breast (my own fault), but in hindsight i could have ran some straight edges up either side and bonded the lot up.

Bonding would have worked a treat on that John, whether you used straight edges or beads on the corner. Try a wall with Bonding the next time, and see how you get on. I normally coat with bonding in the morning, and multi finish afternoon. Twice the work i know, but never a problem with the finished job/look.

 

[1john]

i have used bonding over black mortar a fair few times, just never thaught to use it completly over plasterboard, will try next time although with a little luck my boarding wont be that bad now i am used to the foam adhesive. if i wasnt that shy for room i should and would have much prefered to batten and boarded.

 

[minoka123]

hi
id say use fibre tape its self adhesive thinner and lighter mainly cracks come from shrinkage