Hardie Board - White stain/build-up

Hardie Board about 5 years old. Have visited twice to power wash over this time. There is almost a thin layer of build up that wont come off. Tried light scrub with soap and a sponge/magic-eraser. Will fade/disappear for a day but then it comes back. Looks as if it might have bled from behind the boards. Any ideas on cause and how to get rid of (or reduce) this without stripping the area.

Welcome to the forum. Punch hardie board siding into the search box. Read the covering of this subject previously. Again - welcome.

@bills4065 Thank you, and thanks for the welcome.

Search is how I wound up here, as I didnt find anything directly related[1]. A couple posts about oxidation that didnt quite fit.

Moved an efflorescence search. Im just trying to more accurately identify “what” I might be dealing with here to start a more educated search.

1 - Search results for 'hardie' - Pressure Washing Resource

Hardie board has cement fibers in it and when moisture is able to get behind it, like when you force water by powerwashing into gaps like those shown in the photo, the results often times is that you get efflorescence. The cement fiber absorbs the moisture and as it eventually drys out it drips out the salt deposits leaving the stains.

You can try using an acid to remove it, but like I mentioned earlier those butt joints and gaps really need to be addressed first or it will keep happening.

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As you are aware, hardie board is painted cement. Looking at that picture I would rub my fingers around the areas of run down. It looks to me like you are dealing with an oxidizing paint issue. Was the siding like this before you washed it?

I don’t thing that’s oxidized, at least that’s not what oxidation typically looks like. @cgmckeever also said he scrubbed it with a magic eraser and you would see the oxidation disturbed if that was the case.

@cgmckeever do you know if this was painted at the factory or on site? I never have issues with Hardie that was factory painted, but have heard horror stories about people washing them once they got painted.

yeah, aware of hardie board as painted cement substrate. The siding was NOT like this on first wash 2 years ago, but was there before the current visit.

Rubbing my fingers around the area, am I looking for a “dusting” type of residue on my finger or something else? Ive done that previiously, and the material feels “chaulky” but it doesnt collect on my fingers, like Ive seen on some other posts. The discoloration areas def have a different feel almost like a build up

Yea Hardie board feels a little rough, not smooth like vinyl. When rubbing your fingers on it you would see the house color (slightly lighter) on your fingertips. That would indicate oxidation along with sections where the water has disturbed the oxidation and has caused streaking and fading. But that is still typically the same color as the house, just a different shade not white, and not like this dripping effect.

Your first wash 2 years ago- the siding about 3 years old at that time. This is definitely starting to look like water getting in behind the siding causing efflorescence issues. Does the staining go much higher than the picture you posted?

I cant be certain, but I know this hardie is 5 years old, but Im assuming it comes from the factory painted – and outside some touch ups, it hasnt been painted on site (from what I gather)

The picture is about the focal point of where it starts. Does not appear much higher, at least anything of notice.

@OhioFloMo I cant be certain, but after the magic erase/soap treatment it looks to go away. But then I came back a few weeks later and there is was. Like I never did anything. I cant tell if this is new build up or if it appears to go away, but really didnt.

It can come primed and ready for paint or painted from the factory. I can’t really tell from the photo, but do the nail heads look like they were patched and then painted or just painted over? Thats usually the dead giveaway if it came painted or not. Regardless I don’t think that matters as much in this instance, but it’s something to be aware of for future cleanings… if I take on a post-install paint job I test spot at a much hotter mix then the typical house wash to verify before cleaning. Factory paint holds up/adheres much better in my experience.

Try removing the lowest staining, without getting water on the boards above/into the gaps. Come back a couple days later (hopefully with no rain in between days) and see if it’s still there. If you continue to reintroduce moisture behind the boards it will continue to come back as it dries. You will probably need to use an acid to remove it, I’ve heard some success stories with vinegar or a limestone/calcium remover. Worst case scenario is it doesn’t go away and the boards need to be replaced/painted… but with how separated they look to be in some areas, thats probably the way to go regardless.

Agree. Clean an area with mild acid without getting water into gaps or behind boards. I hope I am wrong, but my gut is telling me this is a efflorescence problem. You may have made someone else’s problem your problem. What has home owner said?

“What do you think is causing this discoloration, and can we try something that wont make it worse” – more or less the ask. So now Im trying to figure best path forward that hopefully can lean more towards removal or les intensifying it rather than rust replacing this streak with a “bleached” stream in its place … LOL

@bills4065 can you elaborate on “this is a efflorescence problem. You may have made someone else’s problem your problem” … ? Are you saying that if its efflorescense, I should acknowledge this and then not attempt anything? Totally fine with that, just want to provide the best diagnosis before i go hands off … I take it efflorescense is something that doesnt have a striaghtforward resolution?

All I am saying is if it is efflorescence- yes it can be fixed. In my 15 years of washing, if there is a problem after a contractor does something at a home, the homeowner holds that contractor responsible for what ever they perceive went wrong. Did you discuss the staining with the homeowner before you washed it this time? You said it was there before you started the wash- homeowner must have been aware of that.

ah, yes … called out before starting. After completing, was asked to give it some more attention, and that was the magic eraser. Results were great … but then it came back, called back for the assessment – and now getting the diagnosis and/or recomendatitons

Let him know whats causing the issue:

“there is moisture getting behind the boards because of the gaps and when the cement fiber dries out the result is the salt staining (called efflorescence) that you see.”

There are chemicals that can fix it with varying degree of success… but it’s labor intensive, time consuming, and can end up doing more damage if you aren’t careful. You can try using an acid to clean it, get on a ladder above the stains, and gently rinse downward… the key is to not reintroduce water forcefully up into the gaps. That may take care of the majority of it, but there is also no guarantee it will remove it all.

Thankfully you have it acknowledged that it was there before you cleaned it (always take photos before/after of problem areas) and that it wasn’t your fault… the best path forward is to let the owner know they should contact a siding company and see if they can at least seal up those areas so no moisture can reenter (if thats even possible) or replace the boards/repaint them. Then wipe your hands of the situation. You didn’t cause the damage so aren’t liable since it was discussed, you tried to make it better but can’t, end of story move on.

this has all been insightful and appreciated. Thank you