Blown plaster on walls

[TheMitchells]

In our Victorian end terrace renovation, some of the bedrroms have plaster which has blown and feels hollow when tapped.  The outside end gable wall also has cracks and render which looks like it is coming off, but high up so hard to see.

I gave the bedroom wall a tap with a hammer and look what happened! 

You can see the gap between the brickwork and the plaster.  Thats looking up the wall to the ceiling.

This is the stuff thats beneath the plaster and on top of the bricks. 

It looks like concrete with small stones and varies in depth but mainly about .5-1cm thick. 

As you can see, mostly I can just pull it off. 

My questions are:-  1.    Should I remove all the plaster from the whole wall or just the parts that are loose?  Its a much bigger patch now but the rest seems solid.

2.     Does the answer above depend on whether we replace with normal plaster or whether we use lime based plasters on the wall?

3.     And how do I tell if lime based products have been used?  Does the greyness and hardness indicate its cement based and not lime?

 

Ideally we'd like to use lime products as it is an old property and thats what we are told it should have.  Which would mean the end gable wall also needs all the render removed and replaced with lime render.  The front of the house has a new cement based render applied when some remedial work was done in 2015 and it was all painted.  It looks great and so we dont want to take all that off too.  Would it matter if there was a join at the corner of the two types of render?

Or can we just replace with cement based stuff and pass on the problems to whoever is in the house in another decade or two?  (least favourite idea)

Sorry for all the questions - I only intended to ask one.

 

 

Edited July 8, 2016 by TheMitchells

[nod]

Unfortunately old sand lime plaster doesn't last forever The sheer thickness  causes it to go hollow in places If it is so loose enough that you can get a scraper behind it to remove. Then the whole wall will have to be knocked off

Don't forget to spray a salt inhibitor on the areas to be patched or replaced

 

 

[Nickfromwales]

If it's an outside wall, definitely a good opportunity to add some insulated plasterboards, but you may have a new wall / old wall look then. If your not re-plastering the whole room then prob better to stick with the old school methods, ( for one wall  ). 

[TheMitchells]

yes, I was thinking about insulated plasterboards and I gather the building regs insists on upgrading insulation if any remedial work is done.  Though what they dont know......

It will not matter about the new look as the whole house will probably need replastering once we have finished. 

Nod - salt inhibitors?? I shall have to look that one up.

Many thanks, Guys.

 

[TheMitchells]

On this same subject, we have decided to apply internal wall insulation across all the external walls, probably using something like Gyproc Thermal Basic which is 22ml EPS on plasterboard.  Its cheap yet will make quite a difference to the uninsulated walls.  however, before we get to that stage, I have lots of holes in the walls.  I applied a 50:50 water/pva glue mix to all the holes last week and now I am thinking of filling in the holes before applying the insulated boards. 

 

Here are a couple pf pics of the sort of holes I am talking about.  there are rather a lot of places like this across the whole house.  The walls are either rubble or double brick.  and the rubble walls seem full of holes!

This is a pillar holding up the back wall!  This one is going when we open up between the two rooms but there is another pillar almost as bad. 

 

Should I use a cement mix (like render) or a plaster mix to fill in the holes?  it only has to be roughly smooth as we'll be applying the insulated boards over it.  But I assume the wall should be as level as I can make it and certainly fill in holes where cold air can get in.  The walls are all dry; we have not had any problems with damp on these walls. 

Any advice? 

[Onoff]

Whatever's quickest if covering it up!

 

Just render over the patches tbh BUT...as you've already PVA'd them and it's now dry I'd NEAT PVA it just before you render.

 

Or you could roughly cut to shape (square off if pedantic) some plasterboard and stick that in the holes or EPS depending how deep.

 

I've done all of 'em.

[Nickfromwales]

 

This one is the most problematic I'd say. It looks to have a coat of tanking / liquid DPM on there to me ( the black stuff ). 

Youll need to hack / scrape the plaster off this area as it's clear they didn't prep / apply with the correct procedures which is why the plaster is coming off in such big chunks. 

The first question is why the tanking was applied ? Is this an area below DPM level or with built up,ground outside ?

[ProDave]

That pillar is shocking. I would want to very carefully re point it and fill in every crack and crevice with cement mortar, and put a brick or at least a part of a brick in that gaping great hole.
 

[Onoff]

Didn't take note of all the pics first view, just the first one. I've used liquid DPM myself years ago with some success. From memory you applied one coat then when dry a second and coated it with sand that provided a key to render to which I did. Looks similar on the wall next to the wc.

 

Would it I wonder be worth tanking the wall and boarding over?

 

I've a similar dodgy wall in the bathroom.  Where the window is was a door, where all the render is was a window. The left hand white area is a bit hollow. I've even got plaster been put on top of wallpaper! Hopefully the battens will keep it all in place.

 

 

 

Edited January 8, 2017 by Onoff

[TheMitchells]

it wouldnt surprise me that they tanked the bathroom wall as there was an issue with damp outside that wall along the side alley a few years ago. that got sorted in 2015 and it all seems dry now.  I shall scrap off some of the black stuff to see if I can get a good  key for the render. Hopefully the rest is still sound and I shall check before doing that wall.  Its a small bathroom (2 x 1.5m) so we dont want to loose any more room than we have to. 

 

@ProDave that pillar is going anyway when we get beams installed across the opening.  But the pillar they will be sitting on is almost as bad. I can get most of my fist into one hole and thats certainly something that will be sorted; before the beams go in.  Hopefully that will happen next week!

 

 

 

[TheMitchells]

Change of plan - we are not going to insulate internally as it is just going to cost too much and I am worried about interstitial condensation which may occur if the insulation is not breatheable.  I think I have that right.  But I am wondering about using a thermal plaster.  I have looked  at ALC's Thermalime which is a lime based plaster with insulating qualities.  as the house is in a bit of a state with bits all over the place, my builder suggested that we just use a wet plaster to cover it all up.  And I thought if we use a thermal plaster, we'll gain some insulation as well as making it all look lovely. 

 

has anyone here any experience of thermal plasters? 

[daiking]

@TheMitchells do you use GBF?

 

This question sounds right up their street.

[TheMitchells]

no i havent.  I shall have a look. I did look at a plasterers forum but the replies were a little arguementative so I didnt go any further. 

[Roger440]

On 27/01/2017 at 20:20, TheMitchells said:

Change of plan - we are not going to insulate internally as it is just going to cost too much and I am worried about interstitial condensation which may occur if the insulation is not breatheable.  I think I have that right.  But I am wondering about using a thermal plaster.  I have looked  at ALC's Thermalime which is a lime based plaster with insulating qualities.  as the house is in a bit of a state with bits all over the place, my builder suggested that we just use a wet plaster to cover it all up.  And I thought if we use a thermal plaster, we'll gain some insulation as well as making it all look lovely. 

 

has anyone here any experience of thermal plasters? 

 

No, but im watching

 

Given that im guessing you have no DPC, id check out periodproperty.co.uk for your lime based insulating plaster options.

 

Im going to have to do this, probably next year.