Plaster boards instead of plaster?

[macadonald]

Hi guys,

I could do with wsome expert advise here please. I live in a 1930 style terraced house. On removing the old wallpaper, I'm discovering that a lot of the old render and plaster has blown. My thoughts were to remove the blown patches and replaster. Now I'm thinking that I may as well redo the electrics etc. A complete strip!

I friend builder has suggested taking the old plaster and render off down to the brickwork and then sticking on plaster boards (insulated on outside walls) and then either skimming on top or simply painting.

Would anyone disagree with this? Is plaster board a suitable finish? I know all new builds tend to be plaster board.. the up side is that it's a gaurenteed flat surface, where as some of the plaster I have isn't... I think it may also work out cheaper than the sand and cement and time of plastering again..

Thanks

Kyle

 

[stanna]

The method of sticking plasterboard to brickwork has been in use in Scotland for decades.

It has now become the preffered method in the uk as it is quicker, cheaper (can be done by anyone) and just as good if not better than wet plaster/mortar.

Not sure about using insulation backed boards with adhesive never done it.

As for finish i always have it skimmed rather than using tapered joints and filler as the surface is more impact resistant.

I use full 2400 x 1200 12.5 plasterboard fixed with the proper mix yourself powdered adhesive.

1 25 KG does around 4-5 boards. When putting on do it in dots but close enough together so that when board is applied dots should squeeze and join together. Im sure someone will pull me on this but my method ensures a really tough wall with no voids and is rock hard.

Try and cut boards for entire wall before you start and cutouts for sockets etc as well.

Use a straight edge across a couple of boards to ensure they line up well and are plumb/flat. Keep joints as tight as possible.

If your on a solid floor raise bottom of boards on off cuts of plasterboard till dry to make sure there is no bridge for cold/damp.

Up to you if you use square edged for skimming or tapered for tape and fill.

The adhesive sets really hard and i use it to fill any gaps or open joints before skimming.

All in all a great method which save a packet.

 

[Richard C]

Are the external walls cavity or solid brick? If solid walls, this has to be considered in deciding what materials should be used. If the existing plaster is in a poor way it’s often best to strip it right back but, be aware, when changing/removing more than 24% of a thermal element (the plaster on an external wall), Building Regulations require that the insulation of that element is upgraded to current building standards, if you get found out; but it does happen, usually if your having other work done that requires inspection. If your plan is to upgrade the insulation anyway then fine but, strictly speaking, it’s notifyable building work.

I would always favour a new plaster/render base & skim over dot & dab plaster board with a skim, it is more hard wearing, last longer & will be just as flat if the plasterer is any good; I would never entertain tape & fill. If you want to upgrade the insulation on the external walls, however, it’s not really an option on those; you could still do it on the internal walls though. It will be more expensive than D&D with a skim

 

[ajrobb]

While I accept that a skim coat is tougher, Tape and fill is easy for DIY and can give a flawless surface. A couple of coats of drywall sealer both gives you a vapour barrier and permits the use of steam strippers for wallpaper. You might want to consider battens as an alternative to dot'n'dab as this gives a service cavity for electrics as well as aligning the edges for a novice.

Dot'n'dab is probably not suitable for solid external walls.

 

[Richard C]

Dot'n'dab is probably not suitable for solid external walls.

Depends on the construction, hence my question

 

[macadonald]

Hi Guys,

Thanks for the advice, very interesting. I assume when you refer to dot n' dab, you are implying plaster board stuck on with adhesive?

Regarding the construction of the house, it is a 1930 london terraced house. I don't think it is cavity, but is double skin, i.e. 2 layers of bricks up against each other.

Thanks

kyle

 

[stanna]

If there is no cavity then as suggested mortar render scratch coat mixed with Sika waterproofing fluid then dot n dab (plasterboard stuck to wall with adhesive)
Used this on many refurbs and never had a problem with damp/ condensation.

Might not meet current building regs on U value but this isnt Grand Designs with a 200K budget and if you dont tell them they dont know.
Building inspectors love spending your money on theoretical improvements that are dreamt up in an office somewhere. Unless your going to insulate every external wall then forget it you will only encourage condensation.

 

[macadonald]

Thanks Stanna,

Why the scratch coat? You can probably tell, but I'm trying to avoid having to render/plaster except for the skim finish coat.

Is the scratch coat purely for the waterproof benefits? I've heard that some plasterboards have a foil backing for damp insulation. Could I not paint the wall with a waterproof insulator and then adhere this plasterboard?

If I'm going to go scratch render, I may as well apply a plaster coat on top.

Thanks

 

[Richard C]

If it’s solid brick you need to be careful; Gypsum plaster won’t survive if there is any hint of damp. Conventional sand/cement render can also lead to problems (possibly why the original is now falling off) & dot & dab PB onto that will give cold spots through the adhesive leading to condensation & the eventual demise of the PB; this can occur both between the PB & the external wall & inside the room itself. You could batten & insulate but I would consider using something like this;
http://www.british-gypsum.com/produ...es/gyproc_thermal/gyproc_thermaline_plus.aspx
make sure you use one with an integral vapour barrier.

For the internal walls you can either float & set or D&D plasterboard & skim that to save money but leave a ½ inch gap at the bottom as advised; your plasterer/builder should know all this, if he doesn’t find one who does!

My reference to B. Regs was mainly so you’re forewarned. We’ve had a few peeps on here caught out by the 24% rule while having a BI visit to look at/certify other work but if you’ve got no other work going on then you’re hardly likely to get caught. Complying with Regs & getting certification needn’t cost that much more anyway + you will be able to produce the necessary compliance certification if/when your asked for it.

 

[stanna]

Well if the walls already damp then you need to treat the cause.

I can only give you benefit of my experience and have used the waterproofed scratch coat on many projects including restoring a tudor house with solid walls.

Using Sikka waterproofer is the best product and have never had to go back to a job or had complaints about damp penetrating later on.

Have a number of buy to lets one of which has a rendered solid gable which was wet through right up to first floor. Had no problems since i damp injected it, half inch sand cement render and dot n dab/ skim on top.

The beauty of doing the scratch coat is that you can do it yourself as the finish doesnt have to be perfect. Make sure you use rendering sand.

If you really want to insulate then you will have to do all external walls in the room or you will get condensation on the cold wall.

 

[macadonald]

Thanks for all the advice guys,

Just to be clear, there is no sign of damp in the walls anywhere, but I fully understand the benefit of a waterproofed scratch coat.

Out of interest, I think I noticed it twice on this forum, but Stanna mantioned if you're going to insulate, you must insulate ALL outside walls or I may get condensation.

Is this a rule of thumb? All or none of the outside walls in a room should be insulated. There's no sign of condensation in the house yet, but I have expereinced it badly in a flat we used to live in.

 

[mointainwalker]

All or none of the outside walls in a room should be insulated.

There isn't a direct link , just a behavioural one.

If you insulate any walls, the room- temperature will increase ( unless you actually reduce heating ) and it is therefore more likely that the conditions for condensation ( temp. difference /relative humidity ) on uninsulated surfaces will be met

 

[roughcaster]

Dot and dab (stick) plasterboard to the walls,,,,,, SO cheap and nasty!!!!!! YUK.

 

[Richard C]

Any increase in insulation on outside walls is better than nothing but warm ambient moisture will condense on the coldest surface in the room. If you have 2 outside walls in the same room, you should insulate them both to the same standard otherwise ambient moisture will condense on the coldest wall first. You can get a similar effect if your dot & dab onto solid external walls without any insulation; cold spots occur where the adhesive is in direct contact with the external wall & moisture can condense on these cold spots; one reason why they invented cavities!

This is why I think insulation boards on the external walls is the best solution for you.

 

[ajrobb]

If you insulate any walls, the room- temperature will increase ( unless you actually reduce heating )

Most rooms now have thermostatic controls on the heating, so heating will be reduced by any insulation. Old walls 'breathe' and let moisture out. Insulated walls include a VPL so prevent moisture escaping.