3/4" thick self levelling topping on old conrete slab, without surface preparation
3/4" thick self levelling topping on old conrete slab, without surface preparation
(OP)
The flooring contractor on a project last week placed a 400 square foot area of 3/4" thick self-leveling topping, on top of an existing 50 year old slab, without preparing the surface of the old slab. The topping will be overlaid by a glued down vinyl tile. In my opinion, a topping as thin as this should be bonded to the slab, or it will curl and crack extensively. Our structural office for at least the past 40 years has specified that toppings thinner than 3" must be bonded toppings (although I have done unbonded topping as thin as 2" when forced to). To bond properly, we specify surface preparation, usually by shotblast (trade name Blastrak). However the vinyl flooring contractor insists that this is the way he always does it. I believe he does use some sort of a bonding agent.
The self-levelling topping manufacturer's literature, and instructions on his containers, clearly say that the base floor surface should be shotblast.
Questions:
1. Has anyone placed such a thin topping as unbonded?
2. Has anyone placed a bonded topping without surface prep?
3. How concerned should I be about a 3/4" self levelling topping that has ben placed on an old slab without surface prep?
4. Should we ask for it to be removed and redone?
5. Should we leave it be, but put the contractor on notice that he has not conformed to manufacturer's instructions and we will hold him for all future costs arising out of defects that show up in future arising out of this?
6. Should we ask for an extended warranty?
6. Should we just forget it?
The self-levelling topping manufacturer's literature, and instructions on his containers, clearly say that the base floor surface should be shotblast.
Questions:
1. Has anyone placed such a thin topping as unbonded?
2. Has anyone placed a bonded topping without surface prep?
3. How concerned should I be about a 3/4" self levelling topping that has ben placed on an old slab without surface prep?
4. Should we ask for it to be removed and redone?
5. Should we leave it be, but put the contractor on notice that he has not conformed to manufacturer's instructions and we will hold him for all future costs arising out of defects that show up in future arising out of this?
6. Should we ask for an extended warranty?
6. Should we just forget it?






RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
Check your code. It might require that in the absence of code directive, the manufacturer's specifications must be followed. Check the administrative portion of your building code.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
As for letting the owner decide...only as a last resort. Owners are not considered to be "sophisticated buyers" with respect to technical products and should not be expected to decide to accept potentially defective construction in the absence of such technical knowledge.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
If the owner is looking to you for advice, I would recommend removal and replacement or valid proof of adequate bond for the long term. Bond tests could be done (ACI has a topping bond test). I would do a minimum of 4 bond tests for the area (1 for each 100 sf). Bond failure should occur in the base material, not at the interface or the topping to achieve a passing test.
I would not go the route of an extended warranty without the following:
1. A performance bond on the product
2. Proof of long-term financial viability of the GC and subcontractor.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
I think the type of self-leveling compound that they used is the type that is designed for thin applications as the purpose is to fill in low spots on a slab, so the thinness shouldn't be the issue. I just used some on a home improvement project, and the edges where the compound stops are almost unnoticeable it is so thin. The manufacturer of the product I used I believe recommended or required a primer be applied first, but I would understand shot blasting or grinding the floor to remove contaminants and also open up the pore structure of the concrete for superior bonding.
Isn't grinding or scarifying more common for slab surface preparation than shot blasting? I did do some grinding of the slab where the compound was going to remove the glue from the hardwood flooring, but did not use primer. Also it is my house and the flooring is glue down hardwood, I am not that concerned with minor cracks or bond failure.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
This is not rocket science. It is an easy situation from a technical standpoint to explain to the owner.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
Do you even have the contractual authority to make the contractor rip out something that isn't a like safety issue? It isn't like delaminated floor tile would prevent getting a CO. I think you could explain the potential problems to the owner in simple terms (tile may pop up, sound hollow in places, etc.) and have them make the call.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
To ExcelEngineering - I agree that it is not rocket science - rocket science is perhaps easier to explain than flooring problems. You must be dealing with a very knowledgeable clientel, or you are a persuasive speaker, or both.
dcarr - unfortunately there were no specifications for the project and the written contract was simply a one page quote with a line or two saying they would install the material. If you think that sounds like something run by amateurs, you would be right. However, I don't think something has to be a life safety issue in order to be able to request it be taken out for non-conformance with manufacturer's instructions. In this case though, there is urgency to get the room back in use, so I am not inclined to tell them to rip it out, especially given the good chain drag results.
I initially posted this to sound out whether there was general agreement that the floor slab should have been shotblast, and I think the responses have generally been that it should have been, both becasue this is good engineering practice, and becauae the bonding agent printed instruction says so.
I also wanted to find out if anyone has similar exprience of placing thin topping without shotblasting the salb. To that question I don't think I jave received any answer of actual exprience, and how it performed.
Thanks everyone for having taken the time to provide your thoughts and advice. Much appreciated and value. It was very helpful. If there are any further comments they are most welcome, but I think I have now most of what I set out to determine.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
Ron- Does shot blasting produce a rougher profile (then rotary disc grinding or scarifying), which increases the shear interlock between the two surfaces? Do you have a link or something for further reading on when to use one method versus the other?
I just was not aware of shot blasting of slabs, but these machines are awesome! I like the dust control systems, very clean and seems easy to use.
http://www.youtube.com/watch?v=g7n4taHRy1w
If you are trying to remove adhesive, in my case, this was hardwood flooring glue, do NOT use a rotary grinder with the head that has a few diamond grinding "cleats" like this:
http://www.toolstop.co.uk/bosch-2608602554-diamond...
What happened is the cleats would skip over the glue, and it took a long time to remove the glue by just letting the machine sit on one spot. I needed a head with scrapers on it I think. However, this same head was amazing at grinding the actual concrete, and I had several cracks and joints with slight vertical displacement and was able to grind these smooth and flat very quickly where you could run your foot across it and not even notice the crack/joint.
Sorry, did not mean to hijack the original post, and I guess this isn't a home improvement site. But I have learned a TON from doing home improvement projects, and I think it has made me a better engineer, especially on the forensic side of things...
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
a2mfk, true individual tiles will not pop up. My thoughts were you could get small areas where the topping is cracked and debonded so a section could be looser than the rest. Probably not likely though.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
What was the condition of the slab surface prior to installation of the topping?
What about a layer of cementitious backer board (like for tile), usually comes in 3'x5' sheets and could act as a bridge over cracks or small delaminated areas? It won't help if you get large areas of debonded topping though. Throwing it out there since it is less than $1/sf and fast and easy to install...
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
Again thanks for all the comments and advice. Much appreciated.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
It would certainly affect all the comments above if it was gypsum (I would think).
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
JAE: the self leveling material is Mapei Novoplan 2 Plus which is described as cement based.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
Mapei Novaplan 2 has very tenacious sticky/bond capacity. I saw thousands of pails of it applied to unprepared terrazzo and concrete on a large hotel floor retrofit. The contractor noticed the sub was not doing any mechanical prep to the substrate and forced the sub to get the manufacturers rep visit the project. The rep did bond tests and the results enabled the EoR and GC to accept the installed product application in this instance.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
Ron - you make some additional very good points.
Happy New Year!
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
I read this with interests because I'll also do it. A2mfk, I will re-do the floor by removing all of the old mortar bed. They are just too thick at 2-2.5 inches. I won't do hard screed (paste-like cement mix) for even 1 inch and bonded to slabs, because any deflection of the floor can debond it and tent the screed upward. So I plan to use 1 inch "thick mortar bed" which Wikipedia described as "The thick bed mortar method has been around for hundreds, if not thousands of years. Historically, a sand/cement mixture was mixed with water to a fairly dry consistency and was spread on either a portland cement water paste (neat cement), or over cement powder spread on the surface which is then sprayed with water to create a slurry coat and spread over the surface." This mortar bed not attached to the slabs avoid stress transfer to the tiles. Now my question would be. Can the thick mortar bed be just one inch? Or does it have minimum thickness? In my place we don't have any self leveling grout. We only have sand, cement and adhesive that we use in millions of buildings as mortar bed.
RE: 3/4" thick self levelling topping on old conrete slab, without surface preparation
"Do not allow traffic for 24 hours after installation. Tile should not be exposed to rolling load traffic for at least 72 hours after installation to allow setting and drying of the adhesive."