Rendering over damp bricks (below dpc)

[sylvester2345]

Hello,
A builder has advised that I render over the damp bricks below my DPC. The bricks are unsightly as they need to be repointed and some are badly damaged but he thinks rendering over them is the best solutions. This is a reputable builder off check a trade. I'm dubious as I have read that render won't 'stick' if the bricks are damp?

Thanks,
S

 

[Alastairreid]

As long as the bricks are clean and prepped the render will adhere.

 

[ree]

Checkatrade is a guarantee of precisely nothing except collecting fees from those who join it. For views, google posts ref Checkatrade in moneysavingexperts.com

The "builder" you refer to is ignorant of his craft if he has advised you to render up past the DPC - doing that will bridge the DPC with rising damp.
He is advising you to literally build-in a further difficulty.

Or perhaps he has advised you to render only below the DPC?
You never render below a DPC - if the bricks and pointing are perished then you replace the bricks and re-point the beds & perps.
Rendering over "damp" and perished brickwork will only accelerate the decay.

 

[Alastairreid]

You never render below a DPC -

There a millions of properties with rendered bases! including new builds.

 

[dhutch]

Depends how bad it is and how long you plan to live there, I am doing nothing with mine....

 

[terrypin]

If the brickwork below the DPC is damaged and brickwork above is ok then your DPC is working.
Render could breach this and transfer damp above the barrier, be careful, not a practice I'd recommend.

 

[ree]

Render is indeed applied below the DPC in some houses, S&C plinths are typical offenders - that doesn't make it a correct practice.

Render below the DPC is most often applied to a narrow band of brickwork, and is mostly installed by default to be in ground contact, thereby allowing capillary action, and absorbtion of splash water.

If you disagree, please explain why?

Never render below a DPC.

 

[KenGMac]

I must admit I for one am adamantly opposed to render below the DPC, Because.

Rising ground water is causing the external brick below the DPC to be almost constantly saturated, this in turn in winter caused the faces on some brick to spall off, this because of the water held in the brick freezing in winter, and being close to ground level. Freeing water is OK but when the frozen water thaws there is an up to 75% expansion in volume, which in turn causes the faces of weak porous bricks to simply be pushed off, at the same time the mortar fails following the constant bombardment of the elements.

The bricks below the DPC are also subject to internal pressures from the condensation and any rain water getting through the external leaf of the wall, which then runs down the inner surface of the external leaf lands on the inner surface of the external leaf below DPC.

As regards the last points, water droplets formed on the inner surface of the external leaf can evaporate into the Cavity, that is OK for the wall above the DPC, but if you think about it? the volume of ventilation at the foot of the cavity wall will be minimal. Obviously, if the cavity has been filled with Insulation this = No evaporation of moisture from the inner face of the external leaf, thus exacerbating the volume of water reaching the bricks below the DPC.

If you consider things so far, the below DPC bricks are permanently assailed with moisture from below, the rising ground water, internally as discussed above, and also saturation externally, all the rain hitting this area of brick + rain water hitting the wall above the DPC and running down on to the bricks below the DPC.

If you consider Retro-fitting Render to the brick below the DPC you will place another barrier to prevent the rising ground water and any water from the Cavity from evaporating the only way it can, externally by the passage of wind over the face of the bricks below the DPC.

There are further considerations as regards the Retro-Fitting of a render, such as applying a cement based render to a saturated surface?
How do you stop in the long term rain water entering between the brick below the DPC and the Retro-Fitted render and stop, minimise the Freeze / thaw cycle that will crack up the render?

As you can see, the TV is seriously crap tonight, hence my musings.

Ken

 

[Alastairreid]

If you disagree, please explain why?

Its common building practice in Scotland! with millions of homes having rendered bases without any problems...And the weather is a a lot more severe than down south.

 

[ree]

So capillary action doesn't work in Scotland?

"having rendered bases" is not specific - are you claiming that in Scotland its the common practice to bridge DPC's and make ground contact?

 

[Alastairreid]

Who said anything about bridging Dpc's?

There are millions of buildings with rendered bases!! the render is waterproof!

What cant you understand about that?

Pedant!!

 

[Alastairreid]

So capillary action doesn't work in Scotland

Pathetic.

 

[ree]

I'm sorry that once you feel yourself challenged and boxed in without any technical answers that you resort to attacks against the man.

Now you make an outrageous attempt to wriggle away by expressing surprise that we, and another, have been talking about bridging DPC's. Pathetic indeed.

Capillary action moisture will squeeze up between the render and the brickwork that is rendered. Unless, as above, capillary action doesn't occur around your way?

Waterproofer in render will fail if the material is exposed to constant moisture from ground contact. The render will become saturated.

There are also the other issues discussed by KenGMac which i avoided mentioning to keep my argument limited.

 

[Alastairreid]

You keep talking about bridging the dpc, yet i never once mentioned bridging the dpc with render.

I most certainly do not feel challenged by your bluster.

I do not know who "THE MAN" is

As stated millions of homes sit quite happily with rendered bases without any issues, my own 70yr old home included...all dry and solid...no capilliary action..no dampness...strange eh?? Can you explain that?...



A little knowledge as they say is dangerous.

 

[Alastairreid]

There are also the other issues discussed by KenGMac which i avoided mentioning to keep my argument limited.

You can argue the toss as much as you or anyone else likes...I deal in facts and recognized accepted building practice.

the idea of dampness bypassing a DPC by “bridging” (by pointing or rendered plinths) is greatly overstated. Not least because cement-based mortars and renders are basically impermeable to moisture.

Get over yerself and stop being pedantic.

You are wrong.