Cement render stripping

[tobydog]

Well, I had a go at stripping the first section of the cement today. Too hot to do too much!. We have a cloakroom / bootroom that attaches to the side of the house and I had assumed it was a fairly recent construction. We are experiencing quite a high level of damp in there at the moment. The problem is we can smell it but can't see it because internally it's all dry lined.

The base of the wall (I think the whole wall is all brick but single skin) felt very damp and was covered in a mixture of bitumin and what I thought was cement render. You will see in the pictures that the wall is actually quite old and the various coverings have caused all sorts of damage. Where it is showing a big need for repointing (not rendered but bitumen coated) the old mortar came out like wet sand. No bonding at all in places and I could push a slim tool right through.

I tested a sample of the render and it did fizz in vinegar but felt like cement. It came off very easily and in pieces the size of dinner plates for most of it and the problem is that in most areas it was applied to brick already covered in bitumen :? . The render went into the ground and was saturated at the base. There was the usual distinctive damp smell when it came off.

The plan is to repoint but not re-render. I do though need to get rid of the remaining bitumen. Would NB510 sort this?

The plan is the lower the ground level all around the area by 4 - 6 inches which will clearly help the drying out process.

Any thoughts on this?

Thanks

 

[Zebra]

Well done, yuk, bet you could hear the house breathe a sigh of relief. What's the render above, the pink stuff, cement or lime?

 

[FamilyWiggs]

I'd check those rain/wastewater goods there. The wall is discoloured around that corner. You'll be surprised how much splash-back you get from those pipes as they water hits the plastic grille. One of the jobs on my list is to extend our drainpipes and washing machine outlets down into the hopper (or whatever it is called).

 

[tobydog]

It did breath a sigh of relief but there is a long way to go. You have the benefit of being able to get at both sides of your problems. At the moment I can only get to one. I am 99% certain that the pink stuff is cement but with the usual Weathershield stuff it's hard to tell. Any thoughts on the the Stippers NB510 for the remaining bitumen?

Thanks

 

[plasticpigeon]

I don't know about the stripper I'm afraid. However as a word of encouragement, I think the bricks at the bottom of your wall look ok, they are not cracked or spalled as far as I can see, they just have a few corners broken off. Quite minimal damage I reckon and should hopefully not suffer any more. Perhaps the old mortar will harden up if it dries out, definitely needs repointing as you say.

 

[JoceAndChris]

A very good thing to do for your house tobydog -well done. I'm reserving judgement on the remaining naked thing though, I'm not very clear about how this boot room fits with the rest of the building? And how it will look as an overall scheme? And isn't your building listed? To my eye soft, gently undulating lime render and limewash is as beautiful, if not more so, than old, soft, red brick. You've already got a wooden extension, isn't that right? Adding red brick is going to be more visual clutter in what's now a beautiful and serene composition, but then again I haven't visited so might be entirely wrong.

I haven't tried removing bitumen from brick, I'd give Strippers a ring. I'm sure you'll be able to get it off but how the bricks will look en masse having suffered its application and removal is unknown. I might be tempted just to limewash the brick after stripping to unify with the rest of the house.

Good luck, such a labour of love.

 

[tobydog]

Thanks plasticpigeon. The bricks are pretty good thanks to the render coming off easily. The weird thing is that the bitumen on the non-rendered part looks to have been put onto a very thin (1mm?) cement screed / smeer in places. It was chipping of very slowly but I got bored and decided I'll strip it first.

Joce - at the moment the old part of the hosue is wrong. The new oak clad extension already sits on a bare brick plinth and the old part does the same but is covered in bitumen or bitumen covered cement all round.

The house is listed so at the moment I'm treating this as a 'repair'. I'm taking it back to how it was originally so I have no hang-ups in doing what I'm doing. It will look so much better (I hope). When it's repointed (never done that before but got to start somewhere) I'll leave it bare but if someone (CO?) ever complains that I've removed cement render and bitumen from a saturated plinth wall, I'll just say that it's still drying out :wink: . Unfortunately my house hasn't seen beautiful undulating lime render and limewash for some years but the plan is to change that. My inspiration is a house just up the road which looks fantastic.

 

[tobydog]

FW - I'll check out my waterworks too. That corner was particularly damp but the only water going into that drain now if the rainwater run off. The washine machine has been moved and the sink is used only occasionally. I'll dig out around the 'hopper' for anything bad going on. Thanks

 

[andrew gayton]

is it bitumin or is it coal tar? coal tar is actually vapour permeable.

 

[tobydog]

To be honest, I'm not sure about the part where the render came off. Where it was very damp low down I could actually scrape it off very easily. higher up it's stuck but very thin. Where it was on the un-rendered brick it was almost plastic like. Tough, thick and chewy in most places but brittle in others where it was thin.

If it comes to it, and I do need to paint the bricks again for any reason, there are some companies that do breathable silicate plinth paint. I think it's actually silicate wall paint by another name. Earthborn are one such company.

 

[andrew gayton]

The removal of the render will see some rapid drying. If not, explore the continuity of the drainage. Repoint in a soft non hydraulic mortar (1 part non hydraulic lime 2 parts 50/50 mix of soft and sharp sand) the application of a limewash here will act as a poultice and draw out any salts. I would stick with a limewash cover here to act as both a poultice and a consolidant to the friable surface of the red brick where the fireskin has been lost. As you have what appears to be a modern render above, this area needs to be as permeable as possible - limewash can be coloured with vegetable black if you wish to take that route.

 

[robgil]

NB510 is now described as an adhesive stripper or something. If you have some try a sample area, if not give Sudbury a call and find out what is best. NB510 worked on the black paint around my plinth , but it didnt half make a mess and I wouldnt go hot pressure washing damp brick and crumbling mortar.

 

[tobydog]

Andrew - I did read that Non-Hydraulic is better for pointing than Natural Hydraulic. I guess the obvious thing is that Non-Hydraulic just sets in the presense of air which is probably all it needs whereas Natural will set in the presense of moisture. Would there be any problem with using Natural and just sharp sand given that I have just bought exactly that to rebuild the plinth wall internally as this is likely to remain mildly moist? I'll take a rain check on the limewash until I see how the bricks come up. Might be best solution though. How much vegetable black would you have to add to limewash to get black and not a million variations of grey?. What's the trick? I currently have a new 5 litre tin of F&B white limewash.

Rob - I had a look at the strippers website earlier (I know that is going to get me in trouble with Mrs. T one day!!). NB510 is the correct stuff for bitumen but they do let you buy samples to try out because large quantities aren't cheap. I know I will likely need a lot overall so I'll get more later. Is the trick to do small patches at a time so as to not get in a real mess?

Thanks

 

[TheForge]

Due to the EU ban on DCM in paint strippers I think you might find that Strippers can now only sell NB510 to 'professionals' with the correct certification now, not DIYers as before! If they are still selling to the public stock pile it quick!!

I know Nitromors have completely changed the chemical make up of their consumer products to remove DCM entirely.

 

[TheForge]

Having just looked on the Strippers website it no longer says 510 can only be supplied to professionals - it appears they've found a loop hole in the new law - DCM is banned in paint stripper but not in adhesive strippers (makes no sense, typical EU!), so all the DCM containing products are now branded as resin and adhesive busters (with a stern warning that it'd be illegal to use it to remove paint!).

 

[andrew gayton]

I wouldnt use hydraulic lime for anything other than building a viaduct or possibly setting ridge tiles. there is a myth circulating that all historic mortars were hydraulic but don't get me on that! non hydraulic at 1:2 is the way to go on this. with regard to the plinth 'blacking' I would suggest that you need to establish whether or not it is coal tar or bitumen (coal tar smells like old telegraph poles) as you wouldnt need to obliterate all of the coal tar as it is vapour permeable and bitumen isn't. I havent used vegetable black for plinth work as I have always used coal tar. I am not sure that limewash in a tin is the same as 'the real thing'......... I just made up a load for limewashing the house next year; 50kg of non hydraulic dry hydrate, 150 litres of tap water and 1 litre of raw linseed oil. The last batch has been on my flint and brick house for at least 7 years which considering that flint offers no suction is pretty good in my book..........

 

[tobydog]

Forge - thanks for the heads up. See the attached link. This DCM stuff aounds really nasty which, if it's like medicine, means it really works.

The link suggests that we have until 6th December 2012 to use up all existings stocks. I'll order tonight.

http://www.paintingdecoratingassociation.co.uk/main/industry_news_details.php?content=DCM_Paint_Stripper_Ban

 

[tobydog]

Correction - mixed messages abound regarding DCM and not sure which is latest. I'll call Strippers and find out.

 

[tobydog]

So, I've just ordered my 510 trial pack and I wasn't asked if I was a professional!!. As The Forge said previously, it's sold as Floor Adhesive Remover 510 and not paint remover so no questions asked :roll: .

I thought I'd try the trial pack first because for best results it needs a pressure washer to remove the mess. I can't do that otherwise my house wall would probably dissolve. I'm only using it outside so hopefully no ventilation issues. I'll report back after my holiday next week. It looks like I'm about to be dried to a crisp in a scorching Portugal.

 

[robgil]

It was originally sold as a paint remover. It is very good at removing both.