Builder advice needed - Workshop build

MrMickeyD

Well-Known Member
Evening folks,

I'm tearing down an old outbuilding as its just too small, lets in water, cold, dark, etc... and replacing with a new timber framed/clad workshop, sat on a 4" blockwork "ring", on a conc slab foundation. I'm comfortable with the timber work and poured a few slabs in my time, but i'm unsure on this part...

Site is sloping, so looking to dig one end into the slope to a depth of about 750mm. See sketch:

IMAG2256.jpg

I was thinking i'd bring the visqueen from under the slab up the end/sides of the blockwork to above ground level, install a 4" permeable pipe along side the slab and back fill to ground level with a permeable fill material (gravel..). Is this going to be enough to keep the blockwork/inside of the building dry? I've seen a bituminous paint on the back of blocks used before - should i be doing this too? Any particular brands or specifications to be aware of?
Any other water proofing ideas you could suggest for me?

Advice gratefully received.

Mick
 

simonl

Well-Known Member
I would certainly sink the pipe lower, so the whole thing can be expected to spend most of its time drained.
 

Alantoo

Well-Known Member
Evening folks,

I'm tearing down an old outbuilding as its just too small, lets in water, cold, dark, etc... and replacing with a new timber framed/clad workshop, sat on a 4" blockwork "ring", on a conc slab foundation. I'm comfortable with the timber work and poured a few slabs in my time, but i'm unsure on this part...

Site is sloping, so looking to dig one end into the slope to a depth of about 750mm. See sketch:

View attachment 99844

I was thinking i'd bring the visqueen from under the slab up the end/sides of the blockwork to above ground level, install a 4" permeable pipe along side the slab and back fill to ground level with a permeable fill material (gravel..). Is this going to be enough to keep the blockwork/inside of the building dry? I've seen a bituminous paint on the back of blocks used before - should i be doing this too? Any particular brands or specifications to be aware of?
Any other water proofing ideas you could suggest for me?

Advice gratefully received.

Mick

KA tanking slurry is much less costly than Thoroseal (now called Masterseal 581)...both are available from Travis Perkins. information on line. I picked up a Marshaltown hopper fed sprayer on eBay which gets it on very quickly...but you can brush it.

I can't remember now why I was advised against the blackjack stuff...possibly because nothing else sticks to it and we were rendering over, but I don't know for sure.

Alan
 

OISÍN

Well-Known Member
Maybe you should think of making the slab longer into the slope, then bringing the retaining wall to the same level all the way around, if your not under the water table, put the visquine under the slab and up the side to the base, I would they use tanking on roll to seal the walls, you will need to prime the block walls first, then seal the base visquine with a strip of additional tanking, then I would face brick in front the the block, or render over the tanking with some mesh. Use a layer of damp on top of block, for the timber frame still board and apply a lead flashing from the timer frame over the block. When I have done this previously, we used resin to install some M12 SST studs in the center of the block wall to the base, then bolted the stud timber panels to the base, as to ensure the wind loads do not move the building, we used 150mm hollow block filled with concrete, and the stud wall was 140mm with 10mm OSB on the outside with a vapour barrier, on the inside full with insulation with a foil vapour barrier, then apply 25mm x 50mm batten for a service void and finished with 18mm OSB for the finished wall.
 

Chasey

Well-Known Member
It might work for a while but it will eventually fail

Internal tanking systems are OK but the failure rate is high enough with expert application let alone amateur. We gave up on all cementitious and Epoxy tanking and switched to cavity drainage membrain

Its fairly idiot proof.

In fact we are installing it in a basement right now.

Best thing to use would be a Oldroyd cavity drainage membrane system
From memory you need System XV 20 externaly but talk to them and they will help with the design

Call Linol Sherman at Safeguard and say Chasey from Pass & Co sent you. He should be able to sort out a design for you

Cavity Drainage Membranes | Oldroyd

A
 

gelert

Well-Known Member
Newton System is also a good one to look into.Bit of a belt and braces if its only going to be a shed but any continious visqueen or other membeane type barrier ,below and above the sbal will offer far more protection than any paint.
 

MrMickeyD

Well-Known Member
KA tanking slurry is much less costly than Thoroseal (now called Masterseal 581)...both are available from Travis Perkins. information on line. I picked up a Marshaltown hopper fed sprayer on eBay which gets it on very quickly...but you can brush it.

I can't remember now why I was advised against the blackjack stuff...possibly because nothing else sticks to it and we were rendering over, but I don't know for sure.

Alan

Thanks Alan - i'll look at those. I'm not going to have much working space though - with the proximity to boundaries, existing hard landscaping, etc., getting down the back of the wall to apply might be a bit of a challenge.
 

MrMickeyD

Well-Known Member
Maybe you should think of making the slab longer into the slope, then bringing the retaining wall to the same level all the way around, if your not under the water table, put the visquine under the slab and up the side to the base, I would they use tanking on roll to seal the walls, you will need to prime the block walls first, then seal the base visquine with a strip of additional tanking, then I would face brick in front the the block, or render over the tanking with some mesh. Use a layer of damp on top of block, for the timber frame still board and apply a lead flashing from the timer frame over the block. When I have done this previously, we used resin to install some M12 SST studs in the center of the block wall to the base, then bolted the stud timber panels to the base, as to ensure the wind loads do not move the building, we used 150mm hollow block filled with concrete, and the stud wall was 140mm with 10mm OSB on the outside with a vapour barrier, on the inside full with insulation with a foil vapour barrier, then apply 25mm x 50mm batten for a service void and finished with 18mm OSB for the finished wall.

Cheers - good info, but its just a shed at the end of the day.The siting of the slab is fixed and the blockwork has been kept minimal as i'm a much better chippy then i am brick layer!
 

MrMickeyD

Well-Known Member
It might work for a while but it will eventually fail

Internal tanking systems are OK but the failure rate is high enough with expert application let alone amateur. We gave up on all cementitious and Epoxy tanking and switched to cavity drainage membrain

Its fairly idiot proof.

In fact we are installing it in a basement right now.

Best thing to use would be a Oldroyd cavity drainage membrane system
From memory you need System XV 20 externaly but talk to them and they will help with the design

Call Linol Sherman at Safeguard and say Chasey from Pass & Co sent you. He should be able to sort out a design for you

Cavity Drainage Membranes | Oldroyd

A

Newton System is also a good one to look into.Bit of a belt and braces if its only going to be a shed but any continious visqueen or other membeane type barrier ,below and above the sbal will offer far more protection than any paint.

Thanks guys - this is the sort of thing i was thinking, a physical barrier behind the blockwork taking the ground water directly down to the land drain. I'll look at the products you suggest (and give Safeguard a call) - hopefully there'll be somewhere supplying small quantities at reasonable cost.

Mick
 

Tom D

Well-Known Member
We built an extension 2 years ago that involved digging into the hill behind the house, they built a huge retaining wall and then a single skin wall for the house there is a membrane that runs between the two in the cavity. At the bottom of the cavity there is a drain. It’s probably more work building two separate walls but I think it’s pretty fool proof. We’re retaining about 6’ of earth and there’s no sign of damp...
 
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