Plaster - bonding coat layers

[Pecanfan]

Quick question(s) for any plaster experts out there (I'm a total plaster novice btw, but slowly getting the hang of it).

I've got approximately 1" of plaster to apply to wallboard to bring it up to the level of the surrounding walls. The plans was to apply 2 layers of Thistle Bonding Coat followed by the skim coat(s). So far I've applied 1 layer of bonding and wire-scratched it ready for the second coat. This coat is nearly dry now. I didn't think this would be a problem since there was no mention of such things on the packet, but according to the spec sheet on british-gypsum.com, the bonding coat *shouldn't* be allowed to dry out between coats. So...

1. What happens if I apply a 2nd bonding coat to a dry bonding coat?

1. Should I just dampen down the first coat before applying the second?

2. Do I apply the finish (Wickes Universal Finishing Plaster) to a wet, set-but-not-dry, or dry backing?

1. Likewise for the finishing coat, if the bonding / backing *is* already dry (there are some areas of v.old lime plaster which I've already primed with PVA) do I need to damp down before applying the finish?

2. What's the difference between wallboard and baseboard?

1. Anyone have any experience of Wickes Universal Finishing Plaster?

Thanks in advance,

Andy

[stuart noble]

No expert, but I don't think plasterers worry about any of the above. I've seen them polish bonding plaster when they've run out of finishing stuff. A light PVA priming should prevent undue suction from previous coats. Baseboard is just for ceilings I think. Comes in smaller size and can be handled more easily.

[Pecanfan]

Cheers for the info - that what I thought. Just got baseboard 'cause it fitted in the car easier - looked exactly the same as wallboard next to it in Wickes, but smaller.

Andy

[G&M]

I'm no expert either but on changing from this product to the British Gypsum equivalent I found I got a much better finish.

[Mark]

Wickes plaster is Knauf I think, which I have never got on with especially their finishing plaster sold in most diy shops. Perhaps that's why so many people find plastering difficult..?

[stuart noble]

As Metacrawler says on searching for "Knauf plaster"......."Did you mean naff plaster?"

[Mark]

Naff is how I've found it, google found

[Pecanfan]

out there! All I can say is you must be very fit and very patient.

Anyway...

Wish I'd read this before buying 4 bags of the Knauf stuff... :-) D'oh! Only bought it 'cause that's what everyone else seemed to be buying so I (wrongly) thought it must be the product of choice. Oh well, live and learn...

Anyway, after persevering with 1 batch of the Wickes/Knauf stuff (and thinking my plastering technique was to blame) I eventually gave up, went back to Wickes and bought the Thistle Multi-Finish instead. The Knauf stuff would be OK for minor patching jobs etc. since the finish is pretty good without polishing, but other than that it's the work of the devil. The Thistle stuff is MUCH MUCH easier to work with (although it does go off quicker so you have to work faster).

I also sharpened up / rounded the edges off my float, which helped a lot. Never heard of this tip before - found it on here:

Before doing this I had a big problem with trowel marks from the sharp edges of the float.

Also, for future reference, Thistle Bonding Coat should NOT be left to dry out before applying subsequent coats (D'OH!!!). It's so ultra-absorbent the skim dries the second it touches the basecoat and a) makes it completely unworkable and b) stops the skim from sticking properly. I found this out the hard way when a large section of skim 'fell off' the wall. IF the basecoat dries out you MUST re-PVA the wall before applying the final skim.

Anyway, just about got my head 'round this plastering stuff and I'm glad I had a bash at it, but never again. I repeat...

NEVER AGAIN

Andy

[Andrew Gabriel]

BTW, it's a trowel. A float is wooden or plastic (and "floats").

It's normally done on the flat surface of a house brick -- I've posted details before. I wouldn't personally take a file to a trowel. A plasterer would traditionally buy a new trowel and give it to a renderer for a couple of weeks. The sand and cement use will nicely polish up the edges and get the steel springy, and then the plasterer takes it back and uses it on plaster.

[Rob Morley]

You can just dampen the bonding with a water spray, or use a really sloppy mix for skimming.

[Mark]

The

Yes it is, it's the finest smoothest finish but the dam stuff will not polish, so its next to useless for doing a large area. As a diy filler for smallish holes its fine, and probably the reason its sold in the sheds. Never say never, now you should know its 90% technique and 10% effort. :-)

[G&M]

Glad to hear that. I spent hours trying to do so, even using the sponge float Wickes sell next to the plaster, with no success.

[Clint]

Yes u can do two coats to build it out. Personally I'd wait till it s fully dry then aďd pva b4 second coat, some people would just wet it down wiv water but that's more for external rendering, U want the second coat to be pushed into the scratch lines, which should be straight horizontally and not wavy as the second coat could slip down the curves, therefore gripping both layers together. Then flatten and scratch/rub with a plastic float, to a smooth finish. Some people then use a nail scratcher to create a keyed surface for the plaster but I prefer to re pva it the do 2 coats of plaster ensuring the second coat of plaster is slightly weaker than the 1st coat. If u nail scratch it u may find that the plaster produces loads of tiny holes where the nails scratched the bonding the u have to work extra head to smooth them out...or apply a thicker 2nd coat. Hope that helped.

[tabbypurr]

Maybe he's been waiting 16 years for your reply. Get yourself to google groups if you want a saner interface with this place & to not be automatically blocked by nearly everyone.

NT