Standard / moisture / vapour plasterboard on single skin wall

[linus1]

Hello All,

I've gone round and round in circles on this and would appreciate some input please....

Last autumn a workshop was built at the back of my garden, it was built on a concrete slab and constructed of med-density concrete blocks (single skin) with a OSB roof covered EPDM. Last winter I had issues with rising damp, penetrative damp and condensation. I've been addressing these slowly over the year but it has not been simple, for example 2 of the walls are barely accessible from the outside, I've to remove fence panels and gain access to neighbours gardens and even then I've had to work in a narrow 18" gap. However I think/hope I have remediated externally the rising damp and penetrative damp for the main 2 problematic walls (we shall see!). I have also installed a 6" inline fan with the intention to improve airflow and help with condensation (still working out where to add more vents).

This is a workshop and storage area as I have no garage, it doesn't need to look pretty inside but I want it dry and clean. To that end I want to dustproof the floor and protect the walls to reduce dust from the concrete.

I will not plasterboard straight away, I want to keep an eye on the walls for dampness, and if necesaary I will tank the walls with slurry.

But assuming no problems, (or maybe assuming some minor dampness), what platerboards would I be best using please? And should I use dot and bad directly onto the block wall or use batons? I was inclined to use a dry fixing like Soudal plasterboard adhesive foam to stick straight to the walls, but then with batons I figured it would be easier to remove the plasterboard if necessary (e.g. if I needed to add insulation or similar at a later date) and it would also leave a gap in case of any minor dampness.

I will likely leave the plasterboard bare, or possibly paint.

(Not related to this forum group, but I was also considering adding some wool insulation between the roof joists to help reduce condensation, but then I read that this might lead to condensation sitting on top of the insulation (There is not enough room to leave a gap between the OSB board roof and any layer of insulation fitted)).

Any thoughts or advise would be most welcome!

 

[Mr Chibs]

What was the cause of the damp? outside ground level too high?

Was a dpc added when the walls went up? If not, then the damp is always going to rise.

As you are not living in it, perhaps you could screw celotex straight to the walls, tape all the joints then plasterboard.
With foil backed celotex the damp would not make it past the foil vapour barrier, so you'd have a drier room.
You could always do the same on the floor and cover with new floor covering.

You can do the same on the ceiling, but you would need some vents, in theory, if you push this insulation to the underside of the roof, you won't need a gap.
You might be able to get away with 50mm insulation, you probably have room for this?

It would obviously be warmer too!

 

[JohnD]

the concrete floor will wick up water from the ground unless it had a DPM. Did it?

you mention rising damp. Did the walls have a DPC?

You mention penetrating damp. Was this caused by a gutter defect? Is there any cladding on the blockwork to shed rain?

 

[linus1]

Thanks Mr Chibs. There are a couple of causes of the damp. Firstly, no DPC was used. The builders laid a large concrete slab (with DPM underneath) and then build up on top of the slab with concrete block. Water is also coming is through the mortar on the 2 problem walls. This is because the walls were build so close to the garden fences that those 2 walls were built up from the inside and the external mortar was not pointed correct and had gaps. Also there are overhanging trees (not mine) so a lot of foliage falls down the back and stays wet and damp.

Unfortunately I trusted the builders knew what they were doing. If I knew then what I know now, as they say...

Through having removed the fences and squeezed into small spaces I have fixed the external mortar, and I have applied a water seal to the blockwork. At ground level I have also dug down and found the edging of the DPM. I have put a mortar seal in the corner between top of the slab and the bottom of the wall, applied flashband primer, pulled up the edge of the DPM and then applied flashband, finally putting gravel in the gully at the edge of the slab base. It might not work, but I'm hoping it will make a difference.

In terms of the roof, I think I could squeeze in 100mm as the clearance is 95mm. I will be looking to add inlet vents to feed fresh air in and pull it out with the inline fan on a timer.

 

[Mr Chibs]

Sorry to hear this.

You'll just have to do what you can, it's funny but in your last pic, the ground looks dry, but you've probably had good weather over the last few weeks.

I quite like John's idea of some form of cladding, you could knock that up pretty cheaply, wrap wall in membrane, add a few battens, nail something like feather edge to battens, this will shed rain and crap from the trees.

Let's hope your fixes might help.

Does this workshop have a window? just thinking about venting etc.

 

[linus1]

Hi JohnD, DPM and DPC as above. I've clad the front of the workshop for aesthetics and protection, as attached. The 2 problem walls, back and side have narrow gaps and I've gone with water seal, flashband at the base and hopefully better drainage.

 

[Mr Chibs]

Just thought, yes it hurt, you could try out 'dry rods', you drill in the mortar line, low down and pop in the rod... looks like a slimey glue stick, this impregnates the mortar and makes a dpc in the mortar.

 

[Mr Chibs]

Cladding looks good, what did you paint it in?

 

[JohnD]

if you can prevent rain from falling on the edges of the slap, where it projects beyond the shelter of the shed, that will keep it dry. You might be able to lay a course of bricks or something, with the dpm wrapped or jointed under it.

 

[linus1]

Thanks, really pleased with the cladding, it's Cuprinol Garden Shades urban slate, its a very dark grey. I'm also in the process of painting the PVC windows a similar colour with some rustoleum PVC paint.

 

[linus1]

if you can prevent rain from falling on the edges of the slap, where it projects beyond the shelter of the shed, that will keep it dry. You might be able to lay a course of bricks or something, with the dpm wrapped or jointed under it.

I've done that at the back as best I can, I've folded the DPM up, glued in place and stuck flashband so it overlaps. Fingers crossed this will work

 

[JohnD]

a course or two of bricks would be more permanent. There's a type of brick with a sloping top that might be ideal. Queen brick?

"plinth brick"

 

[Mr Chibs]

Please post a pic once you’ve painted the windows. My neighbour painted his windows with Some aerosol from eBay, the finish is very good, he went dark wood to white.

Good luck.

 

[linus1]

Please post a pic once you’ve painted the windows. My neighbour painted his windows with Some aerosol from eBay, the finish is very good, he went dark wood to white.

Good luck.

One window done. I did consider an aerosol, and to be honest I wish I had gone with it. I used Rust-Oleum All Surface Paint, having read good reviews and see people paint PVC window frames and front doors with it. However I was not impressed, it was like using gloss house paint. If it had been on my house I'd have stopped early on and wiped most of it off.

 

[JohnD]

it was like using gloss house paint

what's wrong with that?

I've used non-drip oil-based gloss on plastic, and been pleased with it.