3/4" thick self levelling topping on old conrete slab, without surface preparation

[ajk1]

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?

 

[Ron]

ajk1...the manufacturer's instructions should be followed. Surface prep should have been done. Another contractor with 1 year of experience, 20 times.
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.

 

[XR250]

Explain the situation to the building owner and let him decide.

 

[Ron]

ajk1....the bond will likely last just past the contractor's warranty. If you specified the topping, hold them to the manufacturer's specs. Even if you didn't and had some product review capacity, hold them to it. Remember...it is your liability you need to protect, not the contractor's!

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.

 

[Ron]

Sorry...didn't finish.

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.

 

[a2mfk]

Agree with Ron, do not accept responsibility if they did not prep the floor properly. Although glued down vinyl is probably the most forgiving flooring other than carpet. 400sf and 3/4" of topping is not THAT much to just have then grind it off and do it over right, wonder how much the tests Ron recommended would cost in comparison. I wouldn't want to have to do it though

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.

 

[Ron]

A2....surface prep can vary a lot depending on material used. For epoxy toppings or high quality urethanes, shot blasting is common. Acid etch and rotary abrasion are used for very thin coatings, but can be problematic long term for true toppings.

 

[Ron]

A2....surface prep can vary a lot depending on material used. For epoxy toppings or high quality urethanes, shot blasting is common. Acid etch and rotary abrasion are used for very thin coatings, but can be problematic long term for true toppings.

 

[XR250]

@Ron;

This is not rocket science. It is an easy situation from a technical standpoint to explain to the owner.

 

[dcarr82775]

You will get shrinkage cracks either way (bonded or not). Both come with their good and bad points.

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.

 

[ajk1]

Last evening I chain-dragged the new topping and found no hollow sounding areas except in some localized areas near the perimeter as well as at isolated door thresholds, but I believe this was in some cases due to placing the new topping over other intermediate material which was not bonded to the slab substrate. So although the chain drag does not tell me how well the new topping is bonded, it does tell me that it is bonded, at least for now. Since the topping is a quick drying (24 hour) self levelling material, perhaps there will be little ongoing tendency to curl due to differential shrinkage from top to bottom, so that if it is bonded now perhaps it will stay bonded. It appears that they may have got lucky.

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.

 

[a2mfk]

dcarr- The problems you describe are true for ceramic tile, but not vinyl flooring. I think the main issue is the topping could debond from the concrete.

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-260...d-expert-for-concrete-extraclean-125mm-p16898

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...

 

[dcarr82775]

ajk1, my point with the contract was that you probably have no leverage to force the contractor to remove it. Request all you want, but ultimately the owner will have to make that call whether or not to accept. Did anything actually require installation per the manufacturer's 'recommendations'? If not why would they rip it up and replace it for free? I do think it needs to come up and be done right, but there will be a fight over the $ and it is easier if you have something to stand on.

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.

 

[a2mfk]

dcarr- yep, all bets are off if the topping debonds or cracks, vinyl flooring is forgiving in some senses, but needs a very stable and flat substrate. If the finished flooring was hardwood or a floating laminate, I don't think I would have many concerns. But this should be the owner's decision if it was not done per contract.

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...

 

[ajk1]

Does anyone know what the approximate curing time for the adhesive used in setting the vinyl tiles is, before heavy furniture can be psuhed over the vinyl tiles? Our contact with the contractor is closed down for the new year.

 

[ajk1]

to a2mfk - I have used shotblast to prepare the concrete surface for parking structure urethane waterproof membranes for as long as I can recall -- at least 25 years. It is the standard procedure so far as I know, recommended by all the waterproofers in my area. I use grinding to correct differences in floor elevations and the like. Shotblasting is not effective in removing soft materials like old waterproofing membrane because the shotblast beads just bounce off. To remove old waterproofing membrane, we use high pressure waterblast ("spinjet"). As for shotblast, there are different types of shotblast, some with steel bearings, some with glass beads I believe, etc., but that is straying from my original topic.

Again thanks for all the comments and advice. Much appreciated.

 

[Ron]

Ajk1....curing time will depend on the adhesive. If latex/acrylic, it will take days to cure out assuming little or no latent water in the concrete topping. The more moisture, the longer the curing time. If moist-cured urethane, then likely done in 24 to 48 hours.

 

[JAE]

I hate to ask at this late time in the thread - but was the topping a gypsum based self-leveling topping or a Portland cement concrete topping?

It would certainly affect all the comments above if it was gypsum (I would think).

 

[ajk1]

Ron: the adhesive is Mapei S288 which is a water based rubber resin. I imagine the cure time is short, but I don't know for sure.

JAE: the self leveling material is Mapei Novoplan 2 Plus which is described as cement based.

 

[Ingenuity]

I think S288 is a Armstrong not Mapei product.

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.