Plastering - why leave an inch unplastered at bottom of wall?

[tester]

Hi, I understand this is the norm - but I wonder why - is it to do with expansion / rising damp or something?

[Franko]

So that you don't pick up all the dust and crap on the floor and add it into your plaster finish.

[Lobster]

It shouldn't go below the danp-proof course, for sure - if it does then it often causes problems. I've many times had to cut in back when refurbishing, having ripped off the old skirtings; it certainly helps.

That too! I reckon that's the only reason your average plasterer doesn't go right to the ground - the take about as much notice of DPCs as they do electrical sockets. I had one in last week doing some skimming, and I was tearing my hair out reminding him to plaster *lower* than the 4" from the floor required to be covered by my skirtings (the old skirting having gone, and the wall behind being too grotty for him to take his trowel anywhere near...!)

David

[Lobster]

Oh and PS - the other reason, which also applies to first-floor and higher levels (ie, no DPC) is that you can get floorboards out again after the plaster's gone off...)

David

[FKruger]

The DPC is below the floor surely?

[Weatherlawyer]

A floor carries an amazing amount of vibration. So much so that if the plasterboard was in contact with it, the fixings would fail and the joints would crack. There is also some sound deadening involved.

Half inch gaps are the minimum requirement. Much more than that and you run the risk of having problems with fixing skirting board.

Another point to not is that with dot and dab techniques, the adjustment to plumb is done with packers under the board.

[Lobster]

Well allegedly I suppose. I suppose I'm really thinking of old properties *without* a physical DPC, where it's definitely not going to be a Good Thing having plaster down to the ground. Then again, the old house I'm refurbishing at the moment does have a DPC, but that's at about 1" above the solid floor, and it had been breached by plaster. Don't think there's a membrane under the floor though.

David

[Brian Sharrock]

Can you, please, expand on that? What packers, where? I'd assumed that dot & dab techniques just plonked sufficient plaster to permit the board to be 'plumbed'

[Franko]

When you dot & dab, it is almost impossible to cut the board to the exact height needed - if it is too long or the ceiling is a bit out, the board will become wedged and you'll never get it back plumb and straight. If it is too short - you will have no way of lifting the board to create a tidy ceiling line. I was a dot & dabber for about 15 years (till back went) and always used a

1/2" offcut piece of board under the board to enable a board lifter to be inserted to jack up the board tightly to the ceiling after levelling and if necessary adding packing pieces - hardboard or asbestolux offcuts, nails, screws or anything to hand to create a tight fit. Of course you have to be careful about skirting fixings so only use the minimum packing necessary to enable a board lifter to be used.

[Brian Sharrock]

Hmm; thanks ... I think; Isn't one supposed to board the ceiling first? ... then lift boards towards the ceiling but maintaining the edge vertical (plumb) ... any gaps between a sloping ceiling and the top edges pf the vertical boards to be concealed by coving / caulking. {I thought you were referring to 'out-of-plumb' in the 'towards the room' axis.

[Franko]

You are correct - the ceiling should be boarded first and the wallboard should be plumb in both axis but there should be no gaps if done correctly, a bit of trimming here and there is needed sometimes. If there is coving being fitted, any gaps will be covered but the job will look unsightly until the cove is fitted. If there is no coving being fitted, any gaps can be pre-filled before jointing or plastering but this is not an ideal situation as there is a strong likelihood of cracking around the filled area as the building drys out - it also looks unsightly.