How should I cut Kingspan insulated dry-lining board?

[DavidA]

Hi

I need to cut some Kingspan Kooltherm K17 dry-lining board. I want to make a really nice job of it so that it s not necessary to skim- plaster it when its mounted on the wall.

Kingspan's cutting advice is:

"Cutting should be carried out either by using a fine toothed saw, or by using a sharp knife to cut through the insulation and paper backing of the plasterboard, then snapping the board face down over a straight edge and cutting the paper facing of the plasterboard on the other side. Ensure accurate trimming to achieve close butting joints and continuity of insulation."

I am not sure I understand this. Presumably its necessary to cut through not just the insulation but part-way through the board itself, if one stands any chance of snapping it. I don't know how I would do that.

Please can anyone give me advice on the best way of doing this?

BR

David

[stuart noble]

I'd cut straight through with a saw, plaster uppermost. The plaster will blunt it pretty quickly so use any old saw you have lying around and take it slowly to avoid tearing the paper. If it's anything like the standard foam boards, a sharp knife is not a good method, but anything with teeth just glides through it.

[dom]

It really is as easy a they say.

Best tool I found was one of those snap-off blade knives - so I could extend it right out to go through 50mm kingspan in one go - with a sawing action. A steak knife is almost as good. Use a straight edge.

Then like they say, snap along the line - it jut releases any little bits you missed. Finally score through the backing paper, which is a little tough to get right through with the first pass that went right through the board.

[dom]

Sorry, you were describing kingspan backed PB, not plain kingspan - as I had read it.

[DavidA]

K17 is plasterboard with insulation on the back.

I still don't understand the snapping part - surely the plaster board part is pretty tough. Do I have to cut part way through that before snapping?

[Franko]

As with most types of plasterboard - you only need to score, albeit quite deeply, the first layer of paper, the board will then snap along the weakest point when you apply pressure - as long as you have scored deeply enough then it will snap quite cleanly along the line. The main thing that gives plasterboard its strength is the paper bonded to each side, without the paper it is just brittle plaster. You then fold the board back on itself and follow the score on the other side with a stanley knife. You may need to tidy up the cut side with a surform or carefully with a stanley knife but most often the cut will be tidy enough as it is.

Franko.

[Dave Liquorice]

Plaster is pretty weak, most of the strength of plasterboard comes from the paper on each face. The instructions are fairly clear, IMHO.

You cut through the insulation *and* right through the paper between the plaster core and insulation. Place the board face down (insulation and cut up) along a straight batten an inch or two high aligned with the cut and if the bit suspened is of a decent size it's weight will be enough snap the plaster. So you should have placed the board face down along the batten first, with both sides of the cut supported... You then need to cut through the paper on the face side, this might be the hard part as the weight of the plaster/insulation may well try to tear the paper away from the plaster core.

Pers> I want to make a really nice job of it so that it s not necessary to

How are you proposing to fill the joints? They need to be taped or they will crack with normal building movement. I can't think of way that you can just but join edges without having to skim over the tape to cover it. You can get featheredge insulated board and the tape sits in the feather and you just skim/fill the feather rather than the entire wall.

[Geo]

Very coarse (7tpi) - used it once then went back to the stanley knife saw.

Geo