Post & Ask

Hometalk is where people share and help with everything home & garden

Saint Cloud, FL on Oct 20, 2011

Like Clip

About 2+ years ago we layed pavers on a sand bed over our concrete pool deck.

About a year ago we had someone pressure clean & reseal them. Now we are getting what looks like black mold coming up in the cracks of the pavers. Need a solution or someone who knows what to do the clear this up before it spreads all over the deck.

Like Clip

Pool deck pavers showing the black mold?

36 Comments Displaying 25 of 36 comments | See Previous

Woodbridge Environmental ... Colonia, NJ

Just do not let homeland security or DEA know about it. ;-)

on Oct 21, 2011 · Like 2
Hewitt Remodeling Service... Virginia Beach, VA

Kevin,
I get a bit nervous when you take the shop vest off and put the lab coat back on...even if for a little while... CSI: Nederland

on Oct 21, 2011 · Like 2
James S Saint Cloud, FL

Thanks Kevin, will get that sample in Saturdays mail. Looking forward to hearing back from you.

on Oct 21, 2011 · Like 0
JL Spring & Associates Richmond, VA

WoW! Now yer spreadin' that fugi from Fl to Co! Another poster earlier said he was backed into a hill side in NY and was looking for something hardy to grow...this could be the little fungi's lucky roadtrip day! Best to all and I'll be on the look-out for a pandemic!

on Oct 21, 2011 · Like 1
KMS Woodworks Nederland, CO

James...I got the dissecting scope out today...It was in the basement.
Your growth is NOT moss, Nor Mold...But Algae. It is of the filamentous type.... beyond that I would need to run a lot of samples with the "slide" microscope...perhaps I I get more motivated later in the week.
This is a pic I found online that looks similar...In case your wondering what I saw through my scope.
on Nov 06, 2011 · Like 2
James S Saint Cloud, FL

Thanks again Kevin.

on Nov 06, 2011 · Like 0
James S Saint Cloud, FL

Kevin, Would this be Black Algae? Pretty bad stuff to have in a pool and very hard to get rid of.

on Nov 06, 2011 · Like 0
Woodbridge Environmental ... Colonia, NJ

There are chemicals that will kill this algae, but you need to handle it carefully as its not something you want to get on your skin. Bleach nor Clorox will do it. All these products do is take out the color of the algae.

on Nov 06, 2011 · Like 0
James S Saint Cloud, FL

ok, I'm all ears.

on Nov 06, 2011 · Like 0
Woodbridge Environmental ... Colonia, NJ

You can use the same algae chemicals you use for your algae that you use in your pool.. Simply dilute it in a five gallon bucket put it on patio blocks and scrub using a stiff pole brush to loosen up the growth while killing it. Then flush will with clean water.
If it does turn out to be black algae then there is special pool chemicals just for that.

on Nov 07, 2011 · Like 0
Nicholas S Altamonte Springs, FL

I think this goes back to my questioning the sandbed between the pavers and the concrete pool deck. It seems to me this would be the perfect enviorment for not only the algae (pretty cool KMS) but a lot of other things to grow.
It might be a good idea to pull up a few pavers and see what it looks like under there.
The best solution would be to pull up the pavers and replace them with a stamped overlay like ...»
what Sundeck does, though I will miss the continuing saga of The Mystery of The Black Mold.
Hats off to KMS.

on Nov 07, 2011 · Like 0
James S Saint Cloud, FL

Kevin, are you going to be able to diagnose this as to what kind of algae this is (black or otherwise) or should I check elsewhere?
Nicholas, Pavers are expensive and a treatment would be preferable to taking them up and doing a Stamped Overlay approach. Thanis for the
idea.

on Nov 07, 2011 · Like 0
KMS Woodworks Nederland, CO

James...algae is NOT my field of expertise...I studied moss remember. I would hand off a sample to your local pool experts...to confirm for sure. But as mentioned above a basic algae killer should do the trick...I would not be too worried about anything below the pavers...algae needs light to grow...unlike a mold

on Nov 07, 2011 · Like 0
James S Saint Cloud, FL

Sounds good Kevin, thanks once again. Will follow up with the algae treatment and let you know how it goes.

on Nov 07, 2011 · Like 0
Hoffner Nursery & Landsca... Orlando, FL

We stopped doing overlays of thin paves on a sand base and this is one of the reasons, we have been mortaring them down for 8-9 years now and have solved many of the problems associated with installing pavers over concrete. We use pavers from Old Castle most of the time, the thin pavers don't have spacer tabs on them like thick pavers do and do not get poly sand or builders sand on them. What you are experiencing is very common, don't make things more difficult than they have to be, ...»
pressure washing will clean the pavers, be careful not to use to much pressure, or you will undermine the pavers and have them flying off. You can seal the pavers after cleaning them and this will help but not completely solve the problem. It is very important to have VERY dry pavers before sealing them, with theses cooler temps that could be a week after you pressure wash. We have begone to use thinner every time we seal pavers, add about 25% thinner to the sealer this will help avoid getting hazy spots in the pavers.

on Nov 11, 2011 · Like 1
James S Saint Cloud, FL

Well, thank you very much for your advice. Where are you located? From your experience what would you say is the black growth coming up?

on Nov 11, 2011 · Like 0
Woodbridge Environmental ... Colonia, NJ

The sand that has trapped all sorts of organic material is supporting the fungal development. Regardless if its mold or algae. This is why the approach of placing the stones on a bed of cement works better. The sand acts as a filtering agent much like your pool filter. So any organic material such as tiny grass clippings etc become trapped in the sand. With the sand ability to hold moisture your growth begins. ...»

Remove the moisture and the food. Nothing will grow on stone and cement. In fact its not even growing on the sand. Its growing on the material stuck in the sand.

on Nov 11, 2011 · Like 2
KMS Woodworks Nederland, CO

Being an "algae" it is not "feeding" on anything....it is an autotroph which means it produces its own food via photosynthesis. The sand is simply providing a moist environment.

on Nov 11, 2011 · Like 1
James S Saint Cloud, FL

Thanks again, so from what you are saying the best solution would be to remove the pavers, clean away the sand, then relay the pavers on something like a thin coat of cemtent (labor intensive & costly?). If thats correct, what would be the next best solution?

on Nov 11, 2011 · Like 0
Woodbridge Environmental ... Colonia, NJ

Simply using the chemicals and clean. That in your case is what I would suggest you do. It can get pretty pricey taking up the pavers and then resetting them. The cost of the chemicals is not really that much and if it does not work, but i suspect it will. Will not be to much money wasted.

on Nov 11, 2011 · Like 1
Hoffner Nursery & Landsca... Orlando, FL

If you do remove and redo the over layed thin paves the mortar used is very important, it must be for outdoor use and made to adhere concrete to concrete I get it in the tile department

on Nov 12, 2011 · Like 3
KMS Woodworks Nederland, CO

Algae-cide is cheap...moving rocks is not. Spray -scrub - rinse ....done. Repeat as necessary.

on Nov 12, 2011 · Like 2
James S Saint Cloud, FL

Got that Kevin, agreed, will certainly give it a try.

on Nov 12, 2011 · Like 0
Nicholas S Altamonte Springs, FL

Yep I thought the sand sounded like a problem. I agree with Hoffner.
But in the intrest of saving money using the Alge-cide, as KMS said, should do the trick.
After one good scrub and then once a year should do fine

on Nov 12, 2011 · Like 1
Hoffner Nursery & Landsca... Orlando, FL

I agree the less work the better You will still have the problem no matter how you do the instlll it is just a mstter of how quickly it comes back

on Nov 13, 2011 · Like 2