DPC in a single skin garage

[Tony Gallagher]

I intend to build a double garage with 100mm blockwork and 450x200mm piers at 2M centres. As I intend to use a standard plastic DPC will this not affect the stability as the plastic breaks the bond? Also as the external finish is roughcast to ground level doesn't this bridge the DPC anyway?
I really would appreciate some help on this but please don't tell my missus who thinks that I know what I'm doing.

 

[^woody^]

The weight of the wall is enough to prevent movement, and you should use one of the thicker bituminous felts rather than the cheap polyphene/plastic as these are designed to take the load of the wall and the mortar sticks to it better. Plastic felt is really for a vertical DPC.

Render should finish just above the DPC level and a drip (bellcast) is formed to throw water from the wall face

 

[jeds]

Use a high bond dpc. These offer little tensile bond but do prevent sliding.

 

[Tony Gallagher]

Woody & Jeds:: Many thanks. I will definately take your advice on DPC. (I wonder if the B.Merchant will take this plastic stuff back??)

On rendering!! Hmmm, I did consider a bell cast above the dpc line with a smooth render below but this doesn't match my house (post war bungalow) which is roughcasted to ground level. Nevertheless I will go with this suggestion but out of interest only why don't I have a problem with the bridged dpc in the house...No signs of damp..,no boast render. The cavity may prevent ingress to the inner skin but logically the outer skin should be sucking up moisture with consequential damage to the integrity of the wall or the render??

Thanks again for your help. Great forum.

Tony

 

[^woody^]

It may well be that there is little actual local dampness in the ground to creep up the render - perhaps a sheltered wall or overhanging soffits. And yes any cavity would prevent migration to the internal leaf.

Typically where render does come into contact with the ground, moisture will be absorbed and cause the render to become blown from the wall.
But on the other hand, a strong render well bonded to the wall may last many years in this situation without becoming detached, but it does not make it correct, and may not work the next time it is attempted!