Damp Proofing before Rendering and Plastering

[shammyk]

Hi All

I would appreciate any advise you can give, i have stripped all the walls in my house to bare brick, some of the extranal walls are showing signs of water coming in. i am concerned that once i have had them rendered and plastered they may let damp through and start discolouring the walls.

i wanted to address this issue before i had all the walls rendered, can someone please advise

i have read something about PVA coaght first but i am unsure exactly what that is and what it will do

i plan to use render thats 3 parts sand and 1 part cement. Is this sufficient to keep the walls from bleeding water or is a different render mix better

i would appreaicte any help you can give me

Thank you

 

[Bedrock9]

How can you tell water is coming in? I would guess whoever responds to this will want to know whether it is still wet, above or below ground level (retaining walls etc), why you took all the plaster off.

In short try and figure out why it is wet first. Some Damp patches could be nothing to do with what you think. Anyone responding will probably ask if you have any suspicions of where it came from and why first. I.e. treat the source first, bad guttering, failing pointing, cracked drains etc.

 

[shammyk]

i tore all the prvious plaster and render because the property is 140 years old and i wanted to redo the house from scratch before moving into it.

there are a few spots on the exteranl walls on the second and third floor that are showing moisure on the inside

what i really wanted to know is that once i have put two layers of 10mm render (4 sand, 1 cement, 1 lime) and then finishe with 3mm plaster will any moisure still come through or will it get stopped at the brick.

if there is any chance of any coming through should i add any type of waterproofer in the mix to stop it coming through

im planning to get up the side of the house and regrout the areas where the bricks are moist on the inside incase its due to maybe a small hole in the grout

thank you

 

[Bedrock9]

I'm no damp expert, but if they are above ground level I would take some time to try and get to the bottom of what is causing it first.

I am doing a similar project and had damp patches in my two upstairs bedrooms. Several damp inspectors, plasterers etc came around and no one offered any actual "this is what is causing it" advice.

On a couple of sections the plaster came off it was so moist others still had the old lime plaster their with big damp spots.

It was only after the summer being so hot, that I noticed when my dehumidifier was full the damp spots got larger, and shrunk when it was on. This seemed pretty sodding irregular considering there was no condensation and it was bloody hot and dry. Only then did it click that these were all on the various chimneys and nowhere else. One click on Google into sulphur damage to brickwork confirmed what I by now suspected... the bricks were actually sucking up moisture from inside the house.

Turns out sulphur damage in porous bricks works like salt and absorbs moisture. My damp proofing method which is still holding up during a bloody wet northern autumn and winter was 3 coats of gloss paint over said patches.

 

[Bedrock9]

So to clarify what I mean by that you could waste a load of time and effort damp proofing stuff that doesn't need it or you might cover something with rock hard sand and cement render only to have it all fall off again in 3 months.

I am sure more experienced bods will probably echo that point. Definitely try and establish the cause prior to doing your internal work is what almost all the stuff I read said to do.

 

[shammyk]

thanks for that bedrock, however as im at bare brick i was wondering if there wasnt a product on the market that i could spray over all the bricks before rendering so that no moisure gets to teh render and therefore never comes through at all

 

[Bedrock9]

Yes there are various tanking agents you can use which are quite expensive if you are going to apply to whole walls. You could use some cheap wickes bitumen paint which you actually paint over a thin sand and cement skim and then "blind" with sand prior to plastering over with normal bonding and finish. You could also put a waterproofing additive into your sand cement render first.

However if there is a positive pressure of water ingress and particularly upstairs these could have even worse effects like redirecting all that moisture to the places you cannot get too easily like your floor joists if you have wooden upstairs floors. I am not the person to recommend a solution though I think.

I think from the experience of my house though a lot of what other people started flapping about was just simple condensation and a result of old property/central heating/PVC windows disease. Definitely worth getting a dehumidifier in an old house regardless of any damp proofing efforts you take. Mine cost £100 from comet and chews through about 2 litres of water a day. Consider how quickly that builds up inside a house with nowhere else to go and quite quickly you end up with everything being damp and mouldy. Dry your clothes inside and you definitely, definitely should get one.

 

[Bedrock9]

Actually looking at that in more detail again, any reason you are considering sand and cement render? I.e. easier to work with etc?

Are you a novice plasterer intending to do the plastering yourself? Also if you are not living there is the heating on? How long has it been empty? Does it have double glazing? and what areas are showing damp spots? Have you checked for any nearby pipework that could be leaking onto the brickwork nearby as they could be soaking up a leak above or something like that. Again condition of your roof, external guttering etc. Is there anything outside the building near these damp spots. Are they directly under or over windows for example or following the line of a downpipe from your guttering?

Also if you have taken it all back to brickwork building regulations say's you will have to insulate it if solid wall (any more than 50% replastering to a room must be insulated. I assume it won't be cavity wall if that old). If you need building control approval for anything else and you don't insulate it you just want to make sure you don't get into hot water with the building police! Technically then you probably do something like batons, insulation, plasterboard and maybe some kind of tanking if you think you still have a damp issue.

 

[shammyk]

thanks for that Bedrock

the external wall that has shown the internal moisure is a freenstanding wall with no shelter so when it rains it rains directly onto the wall. as its only a couple of small areas that are showing moisture i will grout these areas first to ensure no water is coming through before rendering

the rendering and plastering is to be done by a professional however i wanted to know a few things before i have plasters come in and quote me for the work so i know what i am getting for the price

 

[Bedrock9]

I probably hijacked this thread.. too much coffee today or bored of work etc.

Treat the cause is I am sure what you will be told to do before finishing inside.

 

[Micilin]

I probably hijacked this thread.. too much coffee today or bored of work etc.

Treat the cause is I am sure what you will be told to do before finishing inside.

Not hijacking - exploring!