Epoxy over Micro, over dry pack / mortar bed ?

4 replies [Last post]

Any body ever put a epoxy or Micro topping over dry pack / floated mortar bed. Customers want to save money, and not use self leveling underlayment, and go with a dry pack to level floor, then Micro to smooth it... Then epoxy.... Will this Crack? Anyone have experience with dry pack substrates? The floor goes from 1.5 inches to 3/4.. Any advice? Epoxy iber

Lindy A.'s picture
Lindy A.
All concrete, cementious

All concrete, cementious toppings, and dry pack/floated mortar can crack (be it from stress, shrinkage, lack of necessary reinforcement of some type/etc.  When you say dry pack (as is sometimes used over concrete to level it our or obtain desired slope, prior to applying the thin set used with tile ... are you referring to: 5 parts sand to 1 part portland, with just enough water for it to hold together (hold its shape when clumped in hand, sort of like if you were making sandcastles at the beach;  Would you be adding water or latex additive (again, in either case, just enough for it to be damp and clump together).  From what I understand, when cured, the highest PSI it will reach is 3000 and this is a technique used in conjunction with floor leveling that thin set and 1/4" tile is to be laid over (not for our concrete resurfacing field).

If you were going to apply an Industrial 100% solids Epoxy over this type of dyi/dry top/mortar bed it would have to be cured out first (it is an unknown to me how long it would take to cure out to the point that a 100% solids Industrial $poxy could be successfully applied over it; could be up to 28 days, might be less, in any event it would be an unknown and I personally wouldn't chance it) ... I have always used proven modified cementious microtoppings over overlayments directly over concrete substrates (Ardex, Mapei, Rapid Set Tru, or equal to other that is in this same type/family).

You might be successful applying a modified cementitious overlayment or micro-topping over a dry pack/floated mortar bed; but, again most of these require a cure out for concrete prior to doing so as well. Even if there was no problem with this, these (dry pack and modified cementious overlayment or micro-topping) are still porous materials; ergo: if the dry pack was not cured out enough  it could still bring bout issues with inadequate cure out of the dry pack as it passes through to the epoxy you want to apply on top. 

In my opinion there is the right/proven/normal way to level out a floor ... then there are the may work, may not work, that may work for a while, then just when you think all is well in the world everything goes to hell (cracking, loss of bond of one of these materials to another, etc). 

Dr J's picture
Dr J
motar bed

Lindy is right on. I had to level a floor that had a 3" slope over 10 ft. I used a mortar bed because of cost and installed it very dry ...close to dry pack.(I know how to dry pack also). I learnt quite a bit during this install about a mortar bed. the final floor treatment was lino so I wasn't worried about cracking so much. After the floor was level I skimmed the floor to "seal " it and get a smoother texture. It worked, but it was a tough way to seal a floor. being a dry bed it sucked the moisture out of anything put on it, it was hard to get a good bond being so porous. When I talked with the manufacturer about this repair, he was amazed that it worked. I had to go and skim and skim with an acrylic based topping mix to finally get a usable surface. In the long run I will use a selfleveller extended with pea gravel to do this kind of install again. I thought I was being economical using the mortar bed, but by the time I was done achieving a surface that could be used by the floor layer, I doubt I saved any money.

All this being said, If you are wanting to install an epoxy floor system, Levell the floor with a proper product, Not a dry pack,...I can think of all the outgassing issues, and curing issues and such that you do not need to hinder your work. Do what is proper and charge for it, and you won"t lose sleep over an install gone bad.

GandCFloor's picture
When i used to work with a

When i used to work with a concreteing comany many years ago, they would regulary use what is called Grano concrete, which is brobably the same thing as you call Dry pack. Any where we needed a 10mm 40mm topping this grano/dry mix never failed us. mixed with fibres or ferro, ie small steel fibres batched in at the plant gave the thin bed great strength and to my knowledge never cracked more than normal concrete would.

also i did install a flake floor in a change room at an alcoa factory which was on an old grano/drypack floor. didnt have a problem there either. i installed a 2-3 mm sl over the top of the existing floor for the flake to adher to. Although an outdated way of doing things and also slow. if the dry pack is installed like what i have seen guys do you will not have a problem with it at all.

Epoxy over dry pack

Thank you for all the feedback, and sorry about my late response... Vegas, and it's bells and whistles had me brain dead for a minute =)
Anyways I ended up talking the customer into going with tile. I told them if they weren't willing to do it right, a beautiful floor with an ugly crack down the middle is probably what they would end up with. And if they where going to cut corners... Tile was more forgiving.
Thanks for all the replies, and support.