Drylining onto external cavity wall


Postby pe+e » Tue May 26, 2009 10:09 pm

The plaster on the external walls of the house i have just bought is blown in a few places (especially where tiles were). I was considering trying to hack out the blown plater and then replaster the big gaps.

however I am also considering drylining it instead to get a nice smooth finish. If I do this, i'll probably hack off all the old plaster. House was built approx. 1970 and has cavity walls (I think it has cavity wall insulation pumped in at a later date as i can see all the capped off injection points on the external walls).

If i drylined, I was just going to wooden batten the internal blockwork and then screw to that. However, from what i read, dot and dab seems to be the best way (dont know if this is stronger but i can understand how it is easier to get plumb/level)

Anyway what got me concerned is when i started reading about condensation behind the boards and the need for insulation and a vapour barrier. Does this apply to a cavity wall? I dont mind putting aditional insulation in as i suppose every little helps but is this a bad idea/unnecessary? And what about this vapour barrier either way? I'm sure my parents house (1985) just has the plasterboard glued to the blockwork with no additional insulation or any VB.

Many thanks in advance.

P.S. great forum...i can see myself spending some time on here!
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Postby pe+e » Wed May 27, 2009 2:34 pm

Another thought I had was to dot and dab new plaster boards over the top of the existing plasterwork. As i say, its not all blown, maybe 20% or so where the tiles were. Or screw the boards on to the existing plaster (screwing through to the blockwork behind.

I may even be going OTT. With the amount of blown plaster, it may be considered better yo just try and repair.
pe+e
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Postby kbrownie » Wed May 27, 2009 6:48 pm

pe+e,
The options are all yours, depends what you consider the easier or better one.
If the cavity wall is free of damp, likely to not suffer from condensation.
You can knock all plaster off and dot'n@dab, you can knock off the loose plaster and dot'n'dab but you must ensure the surface below will hold the boards secure.
I find the bigger the board the easier,
Using a straight edge, spirt level and a square for the internal/external corners.
Apply dabs about every tens inch over board, where wall dips in may have to apply larger dab.
Then it's case of pushing board to wall, straight edge, tap with hammer and check that level and flat in all directions, repeat straight edge/hammer/level until your happy then apply next board as before, checking that it runs true with previous board and joints are level and flat. and so on.
KB
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Postby Perry525 » Thu May 28, 2009 7:12 pm

If you use plasterboard you will have to go to a lot of trouble and expense setting it all up, getting it right taping and then skim coating.
Whereas, if you repair the holes in the damaged plaster - simple to do, and then if you wish, skim coat over the whole wall, job will look just the same?
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Postby pe+e » Sat May 30, 2009 8:05 pm

thanks for both the replies. I have started cutting back the blown plaster to nice neat straight edges. The plaster to either side 'seems' to be ok, i.e. doesnt sound hollow when tapped.

I'm thinking i'l attempt repairing the damaged plaster. If i rip off the old plaster i'l no doubt have to take down the coving then this will damage the ceiling so i'll end up drylining all the walls and re-boarding the ceiling- which will be a lot of work!

Any recommendations on plaster type/brand to repair the holes. It is going onto breeze block and/ or brick. I was thinking of getting the whole room skimmed once i've repaired it all so i was thinking i wouldnt bother trying the use a 'base' plaster, leavinng slightly shy of the finishd surface and then using a topcoat. Does it sound reasonable to just use one type and fill it to be flush with the current surface finish?

I have used little 5kg bags of multi-purpose plaster in the past and it seems quite good- nice and sticky so stays in place and sets rock hard (some plasters seem powdery when you scrape away and the inside of them).

thanks again
pe+e
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Postby kbrownie » Sun May 31, 2009 4:29 pm

Depends how deep the infill is, if your re-skiming the lot i'd consider using browning as a base coat, bringing it flush to current wall finsh then plaster over that. You could use one coat but would end up costing you more money.
KB
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Postby Perry525 » Sun May 31, 2009 5:36 pm

Not only the coving but, the skirting boards and architraves a lot of hard work to get it looking right.
Over the past forty years I have tried most plasters but, I keep coming back to Thistle.
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Postby pe+e » Sun May 31, 2009 7:45 pm

went to B&Q today and noticed Thistle one coat- will this do? Also noticed some B&Q premixed one coat in a plastic tub- saves trying to get the mix right and smooth although will be more expensive! Actually, how well would coving adhesive or dot and dab adhesive (very sticky stuff and tries hard) act as plaster for filling in gaps (the gaps we are talking about are where gas pipes etc used to be?

i note that most plasters say no more than 12mm thick. is is ok to be thicker if over a limited area, i.e. if filling a gap where it is supported on both sides by the existing plaster, can it be thicker?

thank you
pe+e
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Postby Perry525 » Tue Jun 02, 2009 4:55 pm

All that will happen is, it will crack.
Not that, that matters, if you are going over it to finish.
And yes, I've use all sorts to fill holes, and most work.
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Postby ricky68 » Wed Jun 03, 2009 7:12 pm

never try to square the corners as you can make a easy job become hard
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Postby pe+e » Thu Jun 04, 2009 8:40 pm

'square the corners' ...what do you mean, surely the corners need to be squared off?

Anyway, there i was cutting more and more blown plaster off when i just thought 'sod it, i'l strip it all off!' This has taken me 4 days solid to get it back to the breeze block.

I've got someone comming to quote me for replastering it. I'm thinking of wet plaster onto the breeze again as i have read LOADS of things on the internet and it would seem to be a more proper way of doing it thatn dot and dab. I was thinking if it was wet plastered before and it was really hard to get off (where it wasnt blown), then this must be a good way of doing it. I was going to re-mortor a lot of the breeze block to I'll have to speak to the plastera dude to see how this will need to dry before he can do his bit.

thanks guys
pe+e
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Joined: Tue May 26, 2009 9:45 pm


Postby kbrownie » Sat Jun 06, 2009 2:35 pm

pe+e,
I think you've taken the right route.
You will hear conficting reviews regarding Plaster Vs Dry-line they both have pluses and minuses.
Job worth doing, a job done well!
KB
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