What is your best bet on this?

Soft Wash with pressure washer?
Roof Pump?

I was thinking strong solution with roof snot.

What’s yall’s opinion?

Roof pump for sure - softwashing with pw won’t touch that. May need some pressure after hitting with roof pump a few times.


+1 roof pump, strong as you can go.

I’ll be surprised if you can get away without using high pressure, unless you spray and leave it to nature.

Another vote for the roof pump. I can’t imagine downstreaming even doing anything to that.

12 v pump -

1 gal SH
2 cups Sodium Hydroxide
1 cup roof snot

Spray first with medium to high pressure. Then hit it with your mix. In the above picture took 4-5 applications to get it all off. Seems like it comes off in layers. I try longer dwells, longer dwells with reapplying mix up to 20 minutes. I had a wall yesterday 160 ft long by 5 ft high yesterday of just what you got. Spent 7 hours and still have another hour or two left to get it all off.

I know this might sound weird, but I find doing 3-4 applications and get as much off as possible. Leave and come back the next day. I don’t know what it is, maybe the mix working over night, but seems like after leaving overnight and coming back the next day and hitting it again, it comes off quicker.

Everyone once in a while, i’ll go to hit it, and it will just come off with pressure - almost like it is wet mildew and not heavy, deep rooted mold. Maybe you get lucky.

Sometimes, I’ll add more Hydroxide and it will seem to help, other times not so much.

Usually, I start with a pump up of 2 cups SH to 1 gal water. Spend 20 minutes increasing strength until I find the right mix that will do something - Not sure where you are at, but here rarely is it hit it with 1%, rinse and get paid. Most of what I seem to do, is like in picture 1 - heavy, baked on mold that has been years sitting on it. In picture 1, I went through 6 gal on SH alone on that section and still not done.


This is part of about 30,000 sq ft restoration job on a baseball stadium that I am working on all this week. I got this all over the place. Pillars here, pillars there, walls all over the place, entrances, exits, building trim, and it just goes on and on and on. The second picture is no so bad - can you tell where I stopped? On the second picture I used a 1 gal SH to 3 gal water mix but still used 12 v and did 4-5 applications. I pre-wet for like 10-15 minutes to try and fill rock with water to keep the SH more towards the surface to reduce oranging of the stones
Third picture is the main entrance after 2 days of working on it. Still got a bit more to go.


Would you need caution painted surfaces with that amount of hydroxide?

Killer truck btw!

Harold - yes. Anytime you put Hydroxide in your mix, be careful of any aluminum (window frames), glass, painted surfaces - basically everything but masonry.

For grins this morning, I got some Scrubbing Bubbles Bathroom Cleaner - it is Hydroxide, SH and Sodium Carbonate in a foamer bottle. Just wanted to test the cling on stone. It worked great and I suspect would use less chemical overall as the chem you are using just sticks to the vertical surface like glue verses watching 1/2 your chem run down to the ground. Gives it plenty of time to work on the mold/algae. I am going to experiment with this theory a bit more by getting some foaming agent from the ag store (they use this in farming for foam application chems) and working with the strength of the mix a bit. BTW - look below - that is this afternoon work when I am done with lunch.

BTW - I have a second 12 v pump (2.1 GPM) that I use just for chem application on stone work. It just the right amount of GPM to give me 35ft verticle reach. I have a gun that has a variable nozzle on it, so I can switch between misting/cone spray to streaming. For higher up, I kinda pump the gun to “shoot” the chem a bit higher and is spreads out the spray. Look at the second picture above. I was able to get that high all from the ground. I do keep my machine running, with my wand next to me, so if any overspray hit the metal paneling or the blue glass, I could immediately rinse off. Happened a few times but no issues with rinsing right away.

Sasquatch - Thanks. Not exactly what I wanted, really wanted a wrap but this was only $1k whereas a wrap would have been $3500… The lighter blue color text doesn’t pop out as much as it did on paper. If I were to do it again, I would go with a darker blue. On paper it popped out good and was in the same color palate as my logo.


I might be old school here but I’d turbo nozzle everything in all those pics


Time is your friend - knock off a thick layer, then allow to dry so that the next chemical application can get into the mess, repeat the chems a few more times over the 20+ minutes then knock off the next layer and repeat…

No miracles on the porous stone/concrete.

1 Like

I’m with IBS, if stone and mortar are solid enough to turbo them that’s how I would attack.
Prob just hit it with DS afterwards to kill residual.
Otherwise layer by layer chem applications and just enough pressure.

I do a ton of this stuff.

John is right - use pressure or turbo to knock off the outer layer. Once you do that, now you have to soak the surface with chem and let it soak in.

After you knock off the outer layer, you have this grayish look to the stones. It is the mold in the pores of the stone. Pressure won’t do anything at that point. You just spray chem wait and rinse. Repeat, repeat, repeat until the chem gets deep enough to kill the mold.


I finally got my 7 gallon a minute, Delavan, 12V and 100 psi pump set up. I have a 1/2 inch supply and exit but I had to increase the exit to 3/4 because I already had a 3/4 chemical hose. I can only get about 1 1/2 story of coverage. Is this because of the difference in diameter in the hose or is this what I should expect?

You will probably be happier with 1/2 or 5/8 hose. Leave the 3/4 feed hose.

Increase your feed line to 3/4, will help some. Also try different nozzles. This one shoots further than any nozzle I’ve ever found and I’ve tried them all if just looking for distance -


You’ll have to convert your end to GHT

Also, length of your hose will greatly effect distance more than anything else.

1 Like