Rendering

[BruceyP]

Hi Guys

DIYer here attempting to re render my house next week and just want to get a few things straight in my mind. I've only ever rendered internally (all be it with nice smooth results) with mortar mix from B&Q!! Apologies if this is the same old question being posted here.

My house is a red brick victorian house in Cardiff. Just wanted to confirm what the best mix would be.

From what i've read for the scratch coat:

4-1 sharp sand to cement + plasticiser

and top coat

and 5-1-1 sharp sand-cement-hydra lime + plastirciser

I don't think i'll need any PVA as there appears to be plenty of key. I'll be using stainless steel beading on corners and around windows, doors etc.

I've also estimated for 60m2 area: sharp sand 1.6 ton, 500kg cement and 100kg of lime

Now I know a lot of the mix has to do with personal preference but does that sound about right for my house and location....i.e. lots of rain!!

The render I have been taking off has been a real hotch potch....some of the older render looks very sandy and just crumbles off, the newer stuff that looks like its been done over old brick upped windows looks more like just cement and has been a real nightmare to remove (but presumably a far sounder render?)

Lastly have any of you guys tried pre mixed renders? Are they any good and if so do you know of a decent product/stockist?

Thanks guys any thoughts/tips that would make life easier would be a great help.

 

[1john]

Victorian red brick, im guessing you have lime mortar and no DPC?

 

[stevethespreader]

i would use 4-1 scratch with waterproofer, followed by 5-1-1 with no plasticiser, the lime you will be using "is" the plasticiser

 

[BruceyP]

Thanks Guys

There has been a retro fitted injected DPC at some point due to the little holes all along the wall, but no original DPC. The wall is solid wall no cavity and the mortar I presume has to be lime due to its age. Black stuff and very crumbly.

Will this effect things?

 

[thatbloke]

It could cause you all sorts of problems, damp being the main one.
I would be rendering in lime if I were you t5o keep the house breathing.

Google for cement render on old buildings to get an idea of what you may be letting your self in for.
Why do you want to render it anyway?

 

[BruceyP]

Well I had considered this. I discussed it with the surveyor at the time I bought the house and his opinion was that lime render wasn't worth the hassle.

The only damp problems in the house were from penetrating damp coming through the large cracks in the old render (the older cement render had been patched and replaced many times and left to blow and crack). Condensation hasnt appeared to be a problem....plenty of ventilation.

From what I understand Cement is fine as long as you treat any cracks etc immediately and has plenty of ventilation inside....and it lasts longer.

Dare I say it, but everyone else in the street has cement render.....can they all be wrong?

 

[stevethespreader]

can they all be wrong?

i told you what i would do, i see no problem in using cement render on red brick, red brick houses do not need to breath as much as stone or timber, but some say if the brick is soft best not to use cement or use the weakest mix you can get away with, if i was you i would rake the joints back by about 10 mm to get rid of the crumbly joints and to provide a key before you put your scratch coat on

 

[thatbloke]

From what I understand Cement is fine as long as you treat any cracks etc immediately and has plenty of ventilation inside....and it lasts longer.

Dare I say it, but everyone else in the street has cement render.....can they all be wrong?

Possibly not, and you would possibly get away with sand and cement.
Lime shouldn't crack if done properly with hair added to the mix.
cement cracks because it is rigid and wont tolerate movement as much as lime which is somewhat flexible. I cant see why cement should last longer then lime, both should outlast our lifetime.