Skimming a plasterboard patch

Why not put a shim behind the plasterboard, on the battens?

That's exactly what I shall do, if the existing depth is indeed too great. But I didn't want to go to those lengths if it's not actually necessary.

Thanks for the thought.

Plasterboard comes in various thickness 9.6mm, 12mm and 15mm. By the sounds of it if you have a 6mm difference you have probably used a 9.6mm thick handiboard in a wall that has 15mm thickness. Unfortunetly to get a 15mm board you will have to buy a full 8 X 4 board. I think you should leave it to your plasterer who may well have some off cuts for small plastering repairs like these.

I have seen people build up the thickness with bonding plaster and a skim or use one coat plaster but how kosher that is I do not know but at the end of the day you have to do what you have to do. Scrim all round and a dollop of SBR is recommended. Alternatively pop round any new build site and they should have plenty off offcuts lying around.

Richard

Thanks for that; I think you're probably right about the patch being thinner than the original: it seems more likely than the plaster skim on the original wall being unusually thick.

I might try Pancho's suggestion of adding spacers to the battens to bring the patch forward to within say 2mm of the surrounding wall.

I would leave the selection of the bit of plasterboard to the plasterer

- who might well secure something in place to his required depth using a smalll kotchel of Bonding Coat or some cove adhesive.

("selection Criteria" might just mean what is to be found in the nearest skip)

He might want to rough up the edges and use a bit of scrim as well.

Murphys Law of Plastering states that: "Anything you do is bound to be wrong and can only increse the cost or time to finish the job"

(There are single coat plaster products available which can easily be spread to 1/4")

Plaster shrinks, so if you are going to build up to 6mm them do it in 2 or 3 passes.

Excellent good advice! Thanks. And thanks too, for introducing me to a new word: kotchel. I'm off now to look it up.

You might have more luck with cotchel! Term for a little bit of something left over.

Yes, I soon discovered the correct spelling as well as the definition. K or C, it's a pleasing word.

Course not. a thick scrape of bonding plaster will easily fill that

You can do that and let him do the fancy finish over the top

Plastering - like bricklaying and most other jobs which involve mixing things with water or handling gloopy ready-mixed substances - has always been something of a mystery to me. After the first few times of trying to do it and making a total botch of it, I decided to accept my limitations.

The reasons for that are fairly simple ..

Almost every other job (bricklaying is actually a good example) can be taken one step at a time, so .. if you lay a brick down then the business of laying a brick next to it in a straight and level line might take a long time for the beginner until you get the hang of it - BUT ... in theory you should be able get a line of bricks laid to an acceptable standard at the first attempt as long as you take your time.

I accept that the mortar will eventually go off and become unusable, but I am sure you get the general point

In contrast to that, plaster has a limited life when mixed, which forces you to complete the entire job / flank / whatever in the time before it it goes off - you cant stop half way across the living room wall

Having got it on the wall, you need to know when to just leave it alone for a while before coming back for the final "trowelling off" (wet decorators sponge in left hand)

Also, plaster has a limited storage life so you need to buy it fresh, which means that any minor patching up job attempted with half a bag of some pink thistle which has been in the garage for a few years is doomed to failure from the outset.

and ... if you dont know how to mix the stuff properly you are wasting your time anyway

here endeth etc ..

Plus a patch of this size the skim should probably extend to two foot further out, or more, than the patch to feather the plaster to the existing wall, to hide the "bump". This does require that section of the wall to be sealed. Easy fill with working time of 20, 40 or 60 minutes could be used and sanded down afterwards but a small bag of this cost twice as much as a 25Kg bag of plaster.

There is a big difference with skimming a whole wall and fixing a patch. The former ideally requires two coats of plaster, roughly flattening down after the first coat and going over the second coat a few times to get a good finish. All stages require some judgement as rework too early or too late and you can mess up the job. Often the trick is to get the plaster on the wall as fast as possible without faffing around trying to get a flat or perfect finish as yu apply each trowel load.

Youtube is a good source of information

For drywall (plasterboard ) repairs some of the Vancouver Carpenter are very good. He does as much drywall as carpentry. California patch

Plastering Yourtube "On the Trowel"

Thanks for those links. I've watched a good many YouTube offerings on the subject,but those were new to me.