Applying Scratch Coating

[self builder 123]

Hi

When applying scratch coating should it be continous over the DPC in the exterior walls of the house down to the ground level, or should there be a break in the scratch coating at the DPC level ?

I was worried that a continous scratch coating would form a bridge over the DPC and thus a path for rising damp ?

 

[roughcaster]

The DPC should "never" be rendered over. There would normally be a S/S or quality galvanised bellcast bead fitted at DPC level, as i notice from the pics,, that your property has. You would have a definite problem if the damp proof course was breached. The ground level around the house should also not be allowed to go above the DPC level

Roughcaster.

 

[self builder 123]

Hi Roughcaster

Our roughcaster has plastered on the scratch coat ( very neat job ) right from the underside of the soffit ( where he has fitted SS stop beads ) right down to the current ground level right over the DPC.

He is going to fit SS render bead at the DPC level ( bedded in mortar while sitting on timber strips nailed onto the wall ) before he applies the top coat and the dry harling chips.

The finished ground level will be 150mm below the SS render bead.

I am a bit concerned about highlighting this as the roughcaster seems very knowledgeable in the aspects of both wet and dry harling and the last thing I want to do is to offend him.

Bottom line - is he wrong ? The base course below the render bead will be smooth rendered which will have Freeflo waterproofer added to it ?

 

[roy c]

He should of set his bell beads on first and scratched down to them. It sounds like he has rendered right down over the dpc so there will be no physical break between dpc and plinth...Usually the ground level should be 6" min. below dpc. sometimes it is not possible to get this( slabbed areas and paviours) but as long as there is a few inches to spare it will be ok....

 

[roughcaster]

I think he's definitely wrong to scratch coat "over" the DPC. I normally fit the beads first at that level, and then scratch,,, but I have also done the opposite,,, scratched down the wall, to just above DPC,, and then,,, from just below it, down to ground level,, and then fitted the bellcast,,, but i have never scratched/rendered "over" the DPC.

Roughcaster.

 

[self builder 123]

Hi Roy C

Many thanks.

Do I need to highlight this with the roughcaster ? Could dampness rise up through the smooth rendered base course ?

 

[roughcaster]

Point it out to him,, query it, because it will be a bridge for any moisture, causing potential damp problems in the future.

Roughcaster.

 

[self builder 123]

Cheers again Roughcaster

 

[self builder 123]

I guess if he is in agreement he could run around the building will his sthil saw and cut through the scratch coat on top of the timber sticks ( which he is going to nail onto the wall to set the render beads on so that he can mortar them into place ) thus removing the bridge.

Would this cut ( the thickness of the blade ) do the job as long as it is below the DPC ?

Fortunately the DPC sits on top of the first 215mm tall concrete block which forms the outer leaf of the timber frame construction. The first concrete block is built off the trench blocks which were built block on flat. This means that the cavity begins 215mm below the DPC

Is this correct thinking or just wishful thinking as the DPC has been bridged by the scratch coat ?