Question for Terry - DPM??

[adm]

Or anyone else that knows a bit about brickwork really.....

What's the correct way to use damp proof membrane? When I build my base, I want to make sure to put some DPM in to stop and damp creeping up the walls.

Do you lay a course or two, then put the DPM on a thin bed of mortar, put more mortar on top of it and then just continue laying additional courses or is there more to it?

[bookemdanno]

Nope! That's it!

Buts its DPM in the footing or foundation, as a thick plastic sheet, sandwiched between the concrete or below it.
And DPC is the tough plastic strip, or bitumen felt or slate within the mortar bed or brick or stonework.

The usual way is get two courses above ground, then bed your DPC as you said and carry on.
You want to see it in the bed of mortar, as its supposed to be a waterproof break and not bridged in any way, by mortar remnants, or render, etc.
Two courses above ground is said to be the norm for rainfall splashback for some reason i think?

Oh yeah, get a DPM in your foundation slab too if its to be the floor for your wood store.

[cannyfradock]

Adm

Danno is our latest Mod (jewel in the crown) and has answered your question but as this was addressed to me I shall give you the common courtesy of my twopenneth worth although it is the same as Dan's response.

The basic principle is dry storage below the oven and no rising damp affecting your slab. The general order of a build is ...Base, Walls, Slab and Dome.

The base is dug out and then filled with rubble/hardcore/scalpings. A sand blinding is laid on top of this so as a DPM (damp proof membrane) ....or thick plastic sheet as Dan stated, can be laid so as no sharp edges will pierce the membrane, then concrete laid on top of this to give a dry surface base.

I use a double wall system for my support walls so I lay DPC (damp proof course) on top of my first block, and the third course of my outer brickwork to stop any rising damp from holding water or splashback. (if I was laying just one wall of brickwork, then I would do just as dan stated....on top of the second course.)

The correct method of laying a DPC is to lay a thin bed of mortar, then lay your dpc on top of this, then lay a normal bed of mortar and lay your next course.......I disagree with this, so i just make sure any frogs or holes are filled, then lay the dpc dry on the wall and then lay a bed of mortar etc..

Hope that helps...

Terry

n.b....as I said ...the same as Danno, but as a stubborn old brickie I do things my way.

[adm]

Cheers Lads,

Here's my plan so far:

1) Pour the slab. This will be 6"+ of concrete with rebar. I will put a sheet of DPM ( the wide stuff) down on the ground and up the sides before the pour.)

2) Lay the first/second/third course of bricks/blocks

3) Add a layer of DPC between this and the next layer. Then carry on.....

So - my worry is, does not the layer of DPC mean that the two courses of bricks/blocks are not physically connected once the mortar dries?

Thinking about this, if you had two layers of plasticine, separated by a layer of cling film, surely they would pull apart easily? Am i missing something here - is it only the weight that keeps it all together, or is there any other mechanical action going on?

[bookemdanno]

There is an element of "stick", but the physics of building level and vertical, weight and gravity hold it all together. If you look at modern DPC, it has a criss-cross pattern into it which is to give a little bit of bite.
Mortar isn't really to stick everything together like an adhesive, it acts more like cream within a cake.

You're in the right ball park Adm, so all's good there!

Looking forward to your build, thanks for sharing.

[faz]

Don't forget that your oven will weigh well over a tonne! That's a lot of gravity holding the bricks together