Exterior Paint Removal from c.1850 House

[RebeccaV]

Hello. Does anyone have any advice about the most sympathetic method to remove external paint from old London Stock brickwork?
The front of my house is painted. There are multi-layers of paint and there is also patches of render on some damaged bricks.
The paint is cracking and bubbling all over but particularly at low-level. I believe it is trapping water within the bricks. Also plaster on corresponding internal walls is damp and crumbling off.
I have contacted various companies who use (i) Therma-tech, (ii) Doff and (iii) chemical softening methods to remove paint but am at a loss as to which would be most appropriate to use on old bricks. Are any likely to cause more damage than others?
Thank you so much! Rebecca

 

[malcolm]

I suspect Therma-Tech and DOFF are the same thing - super hot water pressure washing. You would use a paint stripper/ softener and then blow the softened paint off with one of the hot water pressure washing systems.

Without chemical paint softening the paint the force needed to blow the paint off will be similar to the force needed to blow the faces off the bricks so things like sand blasting would be a bad idea.

Even with the hot water and chemical paint stripper the operator needs to be sensitive. The systems operate at a lot of pressure and the operator needs to be especially sensitive with the softer sandstone window sills. ie if the paint doesn't come off first time then re-apply the stripper, wait a bit and try again rather than just trying to blast that last bit off.

 

[a twig]

DOFF is “more gentle” compared to Thermatech - so less likely to damage but equally less capable at removing stuff. Overall though the difference is small, but to give an example, if you want to remove algae and soot stains from an old cathedral you would use DOFF whereas graffiti removal on more modern buildings tends to use Thermatech.

No stripper or softener was applied by the operators for either system when it was used on my house.

Using chemical strippers is the slow and painstaking approach, and the amount of damage done to the brick will depend on the care that the person doing the work takes when doing the scraping and cleaning

Tried all three on my previous place until we got down to a tanking slurry which some lunatic had applied to the outside of the wall, which ended up having to be spun off with angle grinders and vanity discs

 

[Kearn]

Different view here, the two systems are effectively comparable, brotherly feud resulted in a second company being born. It’s as always, all down to the operator. Speak to both companies, they run accreditation programs, so you don’t just buy the kit and get on with it, and therefore can give you a local list of trained affiliated operators.

Also, chemical softeners ARE commonly used in conjunction with the machines. It makes the removal easier and requires less pressure/proximity/dwell time, all of which are good things to minimise damage.

For the cost of postage alone, send some paint samples to Restorative Techniques, and they will analyse in the lab and let you know what paint(s) you are needing to remove and what softeners may help.

Any operative should also trial before hand to a) demonstrate what’s possible and b) dial in the settings on the kit and also the number of softener applications required so that the job is specced correctly.

We’ve taken a lot of plastic paint off of stone/brick/timber this last year…

The kit won’t damage bricks in the right hands, but it also may not totally clean them. Often there are more horrors hidden under the paint and the fire skins may have been lost through spalling, meaning you can’t really leave porous bricks open to the elements and will need to lime tender / limewash a shelter coat.
Also, sample analysis will help, you may well have different layers of coverings. Plastic paint comes off easily enough, other types, may need another round/different softeners applying once exposed. Limewash won’t budge.

 

[a twig]

Fair enough, guess it depends on the operators then as neither of the two that came to my place used any softeners beforehand. I’ve clarified my previous post to reflect that.

Admittedly it was nearly a decade ago so maybe practices have changed/improved in the meantime

 

[Kearn]

Fair enough, guess it depends on the operators then as neither of the two that came to my place used any softeners beforehand. I’ve clarified my previous post to reflect that.

Admittedly it was nearly a decade ago so maybe practices have changed/improved in the meantime

Always does - just because they are accredited doesn’t mean they are all equally capable/considerate!

We analysed our coatings, thankfully just 2 coats of plastic paint since the 60s, 3 days dwell of two coats 24hrs apart of softener and it fell off. We had the easy coverings…

 

[RebeccaV]

I suspect Therma-Tech and DOFF are the same thing - super hot water pressure washing. You would use a paint stripper/ softener and then blow the softened paint off with one of the hot water pressure washing systems.

Without chemical paint softening the paint the force needed to blow the paint off will be similar to the force needed to blow the faces off the bricks so things like sand blasting would be a bad idea.

Even with the hot water and chemical paint stripper the operator needs to be sensitive. The systems operate at a lot of pressure and the operator needs to be especially sensitive with the softer sandstone window sills. ie if the paint doesn't come off first time then re-apply the stripper, wait a bit and try again rather than just trying to blast that last bit off.

Thank you for the very helpful explanation Malcolm. Much appreciated.

 

[RebeccaV]

DOFF is “more gentle” compared to Thermatech - so less likely to damage but equally less capable at removing stuff. Overall though the difference is small, but to give an example, if you want to remove algae and soot stains from an old cathedral you would use DOFF whereas graffiti removal on more modern buildings tends to use Thermatech.

No stripper or softener was applied by the operators for either system when it was used on my house.

Using chemical strippers is the slow and painstaking approach, and the amount of damage done to the brick will depend on the care that the person doing the work takes when doing the scraping and cleaning

Tried all three on my previous place until we got down to a tanking slurry which some lunatic had applied to the outside of the wall, which ended up having to be spun off with angle grinders and vanity discs

Thank you 'a twig'! I'm getting multiple quotes in and patch tests to uncover what lies beneath. Your previous job sounds...er, hard work! Did you end up having to put some sort of protective coat/weather shield on the brick after using the angle grinders etc, or was the surface/fire skin OK when you'd finished the cleaning job? Thanks again, Rebecca

 

[RebeccaV]

Different view here, the two systems are effectively comparable, brotherly feud resulted in a second company being born. It’s as always, all down to the operator. Speak to both companies, they run accreditation programs, so you don’t just buy the kit and get on with it, and therefore can give you a local list of trained affiliated operators.

Also, chemical softeners ARE commonly used in conjunction with the machines. It makes the removal easier and requires less pressure/proximity/dwell time, all of which are good things to minimise damage.

For the cost of postage alone, send some paint samples to Restorative Techniques, and they will analyse in the lab and let you know what paint(s) you are needing to remove and what softeners may help.

Any operative should also trial before hand to a) demonstrate what’s possible and b) dial in the settings on the kit and also the number of softener applications required so that the job is specced correctly.

We’ve taken a lot of plastic paint off of stone/brick/timber this last year…

The kit won’t damage bricks in the right hands, but it also may not totally clean them. Often there are more horrors hidden under the paint and the fire skins may have been lost through spalling, meaning you can’t really leave porous bricks open to the elements and will need to lime tender / limewash a shelter coat.
Also, sample analysis will help, you may well have different layers of coverings. Plastic paint comes off easily enough, other types, may need another round/different softeners applying once exposed. Limewash won’t budge.

Hi Kearn. I really appreciate all of this information. Thank you for taking time to help me. I've contacted Restorative Techniques re. getting the layers of paint analysed as my next port of call. I suspect I'm heading for paint removal, repointing and some form of weather shield.

 

[a twig]

Thank you 'a twig'! I'm getting multiple quotes in and patch tests to uncover what lies beneath. Your previous job sounds...er, hard work! Did you end up having to put some sort of protective coat/weather shield on the brick after using the angle grinders etc, or was the surface/fire skin OK when you'd finished the cleaning job? Thanks again, Rebecca

It was Bath Stone ashlar underneath all the paint in our case so no, just dressed the stone properly so it was all flat and smooth and repointed it all.