Drying out time (repairing blown render)

GilesMDavis · 25 Oct 2010

Hi there,

first post and I'll make it quick.

A patch of render on the outside of the house has blown.

A friendly builder advised that I should remove all the loose render, brush it out, let the stone dry out and put on 4:1 sand cement mortar.

I've got the loose stuff out but am not sure how long to leave the now-exposed stone to dry

Is it days? Weeks? Months? how do I know when it is dry?

Also as it's rapidly becoming winter and I live in wet Wales, what should I cover the exposed stone with to protect it?

I have another question about flower beds against the house wall - I'll post that in building forum.

Thanks for any advice - I'm a total novice but times are tough and I need to learn!

Giles

Alastairreid · 25 Oct 2010

Depending of the depth of existing render, give it a damp down then a scratch coat of 4-1 with waterproofer leaving roughly 8mm from surface, let dry overnight then a 5-1 mix with plasticiser apply flush rule off then a rub over with a sponge when taking up.

Whats this about letting the wall dry out? is it running with water?

you can get plasticiser waterproofer.

plstering · 25 Oct 2010

(it works for me)
clean out the patch if its dry over the next day or two
then happy days first off
youll need small bags of plastering sand depends on the number of patchs
bag of cement and water proofer
if you want a lime top coat then a bag of lime too
scrach coat of 4:1 mix with a small dash of water proofer in it
start of by weting the wall off with a hose pipe then start laying it on working it in too the adges well and covering all the stone/brick
make shore you have left enough room for the top coat
let it go (2hours) then run some trowel lines in the scrach coat as a key for the top coat
leave it over night
the next morn mix the top coat 5:1:1 if you want lime in the mix if not the 5:1 will be fine you use a dash of water proffer in the top coat if you want but use haif what you put in your top coat wet the wall agen then start laying it on working it in to the adges use a straght peace of wood to rule off the over kill so the patch is flush filling slaks and hallows working it all back over with our trowel leave it to pick up (say 3/4hours) useing a jumbo soft sponge and a bucket of clean worm water
(try puting your hands in cold water this time of year)
rubing over the patch away from you in a circular motion (lihgty)
filling dips with the left over gear keep rubing it up till you think it looks how you want it and dont be shy to rub over the edges on to the old render as it will help to blend in the edges a bit more (can even put a bit of frost proofer in the top coat if ou wanted too

GilesMDavis · 25 Oct 2010

Hi there,

the stonework actually looks fine. Behind the blown render the dusty bits were quite crumbly and looked dry. I guess he was talking about the dampness already in there. (The interior side is prone to mildew).

One point is that the render is really quite thin - not much more than 4mm and then painted on top.

Should I look to add a waterproofer (and plasticiser?) to the mix and then paint over once dry?

What are the products I should be looking for - for the waterproofer and plasticiser?

I think I'll need to get it right in one coat, if I can.

Cheers

plstering · 25 Oct 2010

you can hit it in one cot but i didnt say that ok

plstering · 25 Oct 2010

alastairreid 5:1 then 4:1 the top coat needs to be weeker then the scrach coat but you knew that yer

Alastairreid · 25 Oct 2010

plstering said:
alastairreid 5:1 then 4:1 the top coat needs to be weeker then the scrach coat but you knew that yer

course!!!

typo

roy c · 25 Oct 2010

plstering said:
alastairreid 5:1 then 4:1 the top coat needs to be weeker then the scrach coat but you knew that yer

Wrong way round mucka 4-1 first coat 5-1 top coat

GilesMDavis · 25 Oct 2010

Some members on another thread pointed out that I should clarify it's an old, thick stone building, not modern. (Without a DPC, I'm pretty sure)

In an ideal world it would be lime rendered to let it breathe but it isn't - too expensive/difficult I assume.

So I have a nicely exposed and scrubbed patch of stonework and the blown render is pretty thin

I still need to know if I need to let the stone "dry out"?

And if I'm going for one coat 5:1 or 4:1?

Thanks for the help

roughcaster · 25 Oct 2010

alastairreid said:
"a scratch coat of 4-1 with waterproofer leaving roughly 8mm from surface, let dry overnight then a 5-1 mix with plasticiser".

Click to expand...

Read it again Plstering,,, Alastair was spot on with his advice!!!

plstering · 25 Oct 2010

ITS 4:1 SCRACH COAT AND 5:1 TOP COAT

GilesMDavis · 25 Oct 2010

Just come back, I think I've got the proportions clear now!

Thanks for all your help - I didn't see the replies properly earlier, hence my slightly odd previous post.

Bloody typical but rain's forecast tomorrow, might save me hosing it...

I'll let you know how I get on

Cheers

1john · 25 Oct 2010

Just render it when the weather is fine, you will never get a stone wall to dry out from the outside, the drying time is one month per inch thichness of wall

GilesMDavis · 25 Oct 2010

1John, there speaks a man from Wales

GilesMDavis · 1 Nov 2010

Thanks to a couple of fine days, the render is re-done.

Could anyone tell me how long I should leave it before painting - I've read a few things about taping cling film to it to make sure it's dry but I was wondering if there's a reasonable length of time.

Also, would I need to use a primer on a small patch - it's about a metre square or so?

Thanks

diynot

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Drying out time (repairing blown render)

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