Bubbles/Craters in Cement Based Leveling Compound/SBR mix

[The3rd Earl Of Derby]

So you have covered all areas as to what the problem might be and laid it to the manufacturers instructions? my guess its just a crap product.

-- Sir Benjamin Middlethwaite

[Andy Hall]

Could it be air being released from pores in the concrete?

Often garage floors are not poured with the most TLC or the best concrete....

I wonder whether some dilute PVA put on first would help....

[RzB]

Mark, Many thanks for your help.

NB. The "lumps" in the picture are not because the mixture has not been mixed thoroughly. They are bubbles that have not quite popped...

I have tried a number of methods...

I'm using a mixture of 3 parts water to 1 part SBR. I mix this first in a number of 4 pint plastic containers.

I then take a 25kg bag of the Leveling Compound and put it into a large Trug...

I have tried a number of methods of mixing the two together. My first efforts used a mixer attached to a drill. I would add about 4 pints of the liquid to the compound and stir till all the liquid was taken up. Then add more liquid and stir etc.. This was continued till the mixture was smooth with no lumps.

I too thought that perhaps the mixing method had caused too much air to be introduced, hence the bubbles.

However I have since mixed carefully by hand, using a small shovel. But the result was exactly the same... bubbles & craters.

Thanks, Roy

[RzB]

Hmm.. - I'm beginning to come to that conclusion myself...

Do I take it that this is not an unusual mixture?

Cement Based Leveling Compound and SBR?

Have others used this mixture without problems?

Perhaps I should try a bag without the SBR to see if it's some kind if interraction between the compound and the SBR.

Many thanks, Roy

[RzB]

Andy,

That's a good thought, but on the first section I did make a mistake. I did indeed put down a dilute PVA solution. My mistake was that I let it dry hard. This is evidently a no no because it stops a good bond forming between the concrete and the levelling compound.

This should not be a problem in the first section as it is going to be a store room, with little traffic.

But that would have most certainly have stopped any bubbles coming up from pores in the concrete. But I still got bubbles...

Thanks, Roy

[Andy Hall]

Hmm.... It is starting to look like a product issue.

Is this stuff normally intended for going on as a surface on which to tile etc? If so, presumably small craters wouldn't matter.

Maybe it's time to call it a day and consider something else.

I think that I may have mentioned that I used epoxy floor paint for mine. I was mainly interested in a surface that was easy to clean and wouldn't need to redone for a very long time. It has stood up pretty well to machines (e.g. the one-tonne Felder) being rolled across it.

I used the two stage product from Decorating Direct

by their sealer

is something of a performance because of the minimum (16) and maximum (48) hours recoating period. I had to plan out the whole thing quite carefully, because I already had things in the workshop that I couldn't rehome and obviously I couldn't leave them outside at night, but I could fit everything into one half. This meant knocking up some temporary dollies to move stuff easily and doing one half at a time. Basically, what I did was:

Side 1 - sealer wait 24hrs, move stuff across Side 2 - sealer wait 24hrs. move stuff across

repeat for first top coat then on the final day, take everything out, very early in the morning, and do second top coat all over. Wait until very late and move everything back in. Worked a treat.

[Mark]

So what make of SBR/compound are you using ? With all the SBR admix I have used you are supposed to first lay a bonding slurry, _no_ more then 2mm thick. On top of this you would lay a sand/cement Screed with the appropriate amount of sbr admix, it's always recommended that a concrete mixer or pan type mixer is used for this, paddle and hand mixing just don't work.

Ive never used a floor-levelling compound that can have a SBR admix added, I missed that part in your original post.

one point worth noting is that with all plasters and semi liquid type finishes you should _always_ slowly add the power to the water, not the other way round as you are doing.

-

[The Natural Philosopher]

Did you PVA seal the floor first?

[RzB]

Andy

Yes - the Epoxy paint will go on after the Floor Leveling compound...

The storeroom

has leveling compound then two coats of epoxy paint..

Roy

[Rob Morley]

You should be adding solid to liquid, not liquid to solid.

[RzB]

Hmmm - that's very interesting. I have re-read the instructions...

It does indeed say add the powder to the liquid. See the instructions... SLC.jpg...

this possibly be my problem? Does it really make that much difference? I guess there is one way to find out!...

The instructions say add 25Kg to 5L of liquid. However I have found that the 5L is not enough to get a pourable consistancy. More like 6.

I'll do a test section later this afternoon.....

So you would put "all" the liquid in the trug and then slowly mix in the powder? Yes?

The paddle method and indeed the materials were recommended by the manufacturer after a site visit. The mfg saw this job as having very low technical demands in comparrison to the industrial jobs they normally handle. Overall they have been very helpful and I'm very pleased with the initial room I did with their products - apart from having to fill the bubbles!!!!

Many thanks for your help. Roy

[RzB]

In one section yes, another section no.... Same result...

Thanks, Roy

[Andy Hall]

This really only leaves release of air or other gas as a result of the air being trapped during mixing or other gas being produced from chemical reaction......

[Mark]

Yes absolutely. If it were me, I would first do a small test without the admix, if this works ok do another With the admix. When you are mixing a large volume it helps if you can have one person using the mixing drill and another poring in the power, slowly add more power to keeping the mix liquid at all times without lumps forming.

My mixing paddle runs at about 500rpm any faster then this you risk inducing air into the mix.

Id be interested to know how it goes, as I still think you were mixing at too high speed and also had lumps in the mix.

-

[Mark]

Its does say on the instructions

or porous surfaces should be primed with pva/acrylic primer.

-

[RzB]

Hmmm - I really don't think it was the speed, as I got exactly the same effect when I mixed very carefully with a small shovel.. I have been using one of these...

has a top speed of 650 rpm. I have been running it well down from top speed.

And - no lumps - honest :-)

As you suggest - I'm going to mix half a bag with just water to see how that goes... Using your recommended method..

Then do the same but with the SBR mix.

It will have to be later this afternoon as the "labourer" is working till 4:30... Pah - "working" in a charity shop

- like putting a dog in a butchers shop :-)

I'll feed back as soon as I have done the tests..

Many thanks, Roy

[RzB]

Mark,

Yes - this was discussed with the manufacturer who saw the floor and said it was not necessary to do that. They put that in there for floors that are very porous and in a bad way. That is not the case in this instance.

Also when I did use PVA primer on one section it made no difference to the bubbles... See response to Andy Hall a little earlier in this thread...

Many thanks, Roy

[RzB]

Yes - I think so. Mark in earlier response has pointed out that my mixing method is wrong. So I'm going to give that a try. Also with/without the SBR - that should clear up the interraction possibility. We shall see...

Thanks, Roy

[Stuart Noble]

Having used this type of screed a couple of times (from Builder Center), I'd say the product you have is faulty. Essentially it's some kind of inert mineral (not cement) mixed with an SBR emulsion, except it doesn't actually "mix", but settles out after a few minutes without stirring. The emulsion dries and binds the aggregate. No curing or chemical reaction involved so no reason for air to be finding its way to the surface. I imagine the raised edges of the craters would be more of a problem than the dips themselves.

[RzB]

Hmm - "labourer" returned... not prepared to start work this evening... :-(

Just can't get the staff these days...

Will report back tomorrow...

Roy