We just had 7 yards of concrete poured this weekend. We have been advised by the guys that helped us (pros) that we should wait a week or so and then use muriatic acid to wash down the slabs, dry, and then seal up the 'crete with a commercial sealer.

We also have some old gnasty, gnarly exposed aggregate concrete that was here when we bought the place. It's covered with moss, and dirt and duck "products". I was told we could clean up the old mess with same caustic product.

I am concerned about using muriatic acid on the new slabs and old stuff, just because the cautions on it are pretty scary and I have heard warnings about it for a long time. Short of using a wire brush and what? bleach? do you guys have any alternatives?

Any recommendations for sealants?

I have lovely rhododendrons and azaleas around my old walkway (old aggregate) plus with the critters around I am always concerned about chemicals.

Got any alternative ideas for this?

Thank you so much. I appreciate all the good advice I get here, and since I am going to school full time again pretty soon, I want to get going on this.

-- sheepish (rborgo@gte.net), March 12, 2000

Answers

http://www.geocities.com/PicketFence/Garden/8784/pics/Rock3.jpg......S heepish: Cut and paste this picture of a rock wall of my cabin. I had a terrible problem with white (lime I think) bleeding and I was told the only way to be rid of it was the acid wash. I also did not want this nasty stuff around so I had to keep washing it off and wire brush the tough spots. The longer It's left alone the harder it is to get off. After 6 months I used Thomson's water sealer for concrete. So far a year later no problems. The new pour You don't mention if it's a wall or a walkway. I don't do anything to my walkways. Maybe somebody else knows more that might help me too.....Kirk

-- Kirk Davis (kirkay@yahoo.com), March 13, 2000.

Hi folks! If you do not want to use the acid you can use other products that are safer. You will need to find a supplier to the trade to get the product range of choices to pick from. Look in the phone book under brick or concrete block suppliers and start there. Tell themm you want a masonry washing product called "600 Detergent " I believe it is made by a company called Thoro, but other competitor companies have competing products. This is not as harsh as the acid. A side note on the acid: it should never be used straight from the bottle as it will burn your new masonry surface a ugly brown color which you wont be able to remove. You need to dilute it in water and use elbow grease and a brush. I cannot figure why they are advising you to use acid on your new slabs. On both your new and old slimey slabs just rent a commercial ( at least a 13 hp ) pressure washer and clean them both squeakey clean then go back to the supply house and get a water based silane/ siloxane masonry water repellant and apply it liberally. Cover your plants and dont spray to heavily at the edges.This will seal your concrete and make it easier to get the slime off in the future. Kirk... I think the white stuff you refer to as lime was probably efloressence ( look it up ) a leaching of salts in the masonry mortar mix which usually indicates water IN the wall which you may have resolved with the thompsons stuff. Remember that products like thompsons are only coatings, the commercially available silane/siloxanes are true pennetrating sealers that do a much better and long lasting job.

-- mike (mstydale@aeroinc.net), March 13, 2000.

I agree with avoiding the muriatic acid if possible. You have to be careful not to splatter it and a brush encourages splattering. You wouldn't want that to hit your face or arms. Follow all cautions, as it truly can be dangerous. I really only use it for rusty metal cleaning, and then with great caution.

-- Anne (HealthyTouch101@hotmail.com), March 13, 2000.

More information:

These are slabs: steps, sidewalk, and a pad. All horizontal surfaces. The muriatic acid wash (after the concrete has cured) was to get a nice finish by removing any leftover slurry, as I understand it. Then sealing to protect the finish.

I think I used Thompson's water seal before on a new driveway and wasn't too impressed. The other sealer type sounds good, and I will check into it, as well as the other good suggestions here.

The old concrete has big stones and is really awful ( I almost wrote: offal!) to pressure wash. I will attempt that first, though, and see.

Thanks for your replies.

-- sheepish (rborgo@gte.net), March 13, 2000.

Kirk, BTW, gorgeous wall! Worth all your work, I'm sure.

-- sheepish (rborgo@gte.net), March 13, 2000.

HERE'S THE REAL STORY!

First let's address the issue of Muratic Acid, WWhat is it?......... Where does it come from?........ We know it is caulstic but is it damaging to the enviroment, or insects, etc....??? Muratic Acid is a refined product, made from the stomic acid of slottered animals (ie. cows,pigs) these are the same juices that are found in our own stomics. As a professional concrete contractor I always use muratic acid to further clean the aggregate and also for a slight etch to help reveal small amounts of the sand, this will make the background colour nice and even. it also will remove any lime or calcium leaching out of concrete. Once the exposed aggregate concrete is acid washed and dried. allow the concrete to cure for a min. 7 day's. before applying a DECORATIVE sealer, yes this is to beautify only. I use a product call C.P.D. Acrylic concrete & paver sealer. This is basically a high acrylic (25-28% solids) sealer, usually suspended in xylene (strong smelling stuff) But this sealer will give you that wet shiny look you are looking for. This will also make your old exposed concrete look new again. any further question can be submitted to use @ www.ExposedAggregateConcrete.com

-- Art Sampson (support@ExposedAggregateConcrete.com), April 10, 2001.

HERE'S THE REAL STORY!

First let's address the issue of Muratic Acid, WWhat is it?......... Where does it come from?........ We know it is caulstic but is it damaging to the enviroment, or insects, etc....??? Muratic Acid is a refined product, made from the stomic acid of slottered animals (ie. cows,pigs) these are the same juices that are found in our own stomics. As a professional concrete contractor I always use muratic acid to further clean the aggregate and also for a slight etch to help reveal small amounts of the sand, this will make the background colour nice and even. it also will remove any lime or calcium leaching out of concrete. Once the exposed aggregate concrete is acid washed and dried. allow the concrete to cure for a min. 7 day's. before applying a DECORATIVE sealer, yes this is to beautify only. I use a product call C.P.D. Acrylic concrete & paver sealer. This is basically a high acrylic (25-28% solids) sealer, usually suspended in xylene (strong smelling stuff) But this sealer will give you that wet shiny look you are looking for. This will also make your old exposed concrete look new again. With exposed aggregate concrete I would only recommend using Thompson's Water Seal if you want a matt finish. any further question can be submitted to use @ www.ExposedAggregateConcrete.com

-- Art Sampson (support@ExposedAggregateConcrete.com), April 10, 2001.

Hi Sheepish. I've been a concrete inspector for 22 years. Our lab used to use muriatic acid all the time. Several years ago we switched to plain ol' vinegar. I usually dilute it 5:1 and soak my equipment in it overnight. Nontoxic and cheap. Sandy

-- Sandy in MN (jpevans_56353@yahoo.com), April 11, 2001.

Thanks, all. We have been enjoying our results from last year, and are now considering doing some more....probably later in the year, though. I'll keep this information in mind!

-- sheepish (WA) (the_original_sheepish@hotmail.com), April 11, 2001.