Cement washed (workshop) walls (OT)

[SteveD]

A couple of weeks ago I filled the cracks and holes and cement washed the concrete block walls in my basement. (1 cement, 2 sand + PVA additive). This space will at some point will be my new workshop. Primarily this was to seal where the cockroaches and ants came in and out and also to see if there were any damp patches. After a couple of days I put in a dehumidifier to help dry out the walls. The other day I was checking and I can see a damp patch in one corner (I was expecting it) but I can also see what appears to be dampness on the cement lines between most of the blocks in the rest of the room. That is, the wash over the cement lines is a darker colour to the wash over the block. In fact the cement lines are clearer now than they were before I started. I am likely to be lining the walls with a stud wall and I want to make sure that they are dry before I start. Can anyone tell me if this is an optical illusion, if what appear to be perfectly dry walls are, in fact, damp, or what?

SteveD

 

[Per Swenson]

The mortar betwixt the block sucked the moisture out a da mix.

How do you like that for a sentence?

It will be fine.

Per

 

[dirtydeeds]

per is perfectly correct as he is on many things

a different but the same explanation is that the suction (of moisture from the render) is different between blocks and the mortar, hence the pattern

its perfectly normal and has no noticable effect on adhesion

it will even out in the end, but if you dont like it, paint the walls

 

[b_m_hart]

If you're worried about strength (it doesn't seem like you are), then you want to put a humidifier in there / put some water on it, to prevent it from drying out too fast.  Cement (and concrete) cure over roughly four weeks, so if you're concerned about how it turns out, even though it's hardened, it isn't finished just yet.
http://en.wikipedia.org/wiki/Concrete

 

[SteveD]

I left it for several days (and had gently hosed it down after it had initially set) before dehumidifying. It is only a sealing wash not a structural or strengthening layer. However with the temperature in the 80s (F) and little ventilation if I did not dehumidify it somewhat the walls would turn black with mildew in short order. It is not a problem - more curiosity and making sure that I did not have something else to worry about! The walls will finish up being sealed and then painted - after a few more weeks of 'drying'. The dehumidifier, by the way has generated well over 10 gallons of water (room is 14' square, 8' high) and the humidity is just coming down to 60%.
Thanks for the feedback.
SteveD

 

[Tinker]

Steve, Per & DD are right about the discoloration.  The block and the mortar are of different densities and will suck the water out of your sealer at different rates.  I would be more concerned about why the cracks in the mortar that you were trying to cover up.

I was going to mention something about frost pushing against the outsides of the walls; and then i thought to look at your bio.  If you have a frost problem in Bermuda, we better all leave town.  we would be buried in 10 feet of ice up here in New England.

It is possible the blocks were placed on days it was very hot and the mortar joints did not set slowly enough.  That would cause shrinkage of the mortar from tthe blocks or even a moderate to extreme disintegration of the mortar joints.  I am guessing that second suggestion is not the case, or you would have had problems applying the sealer to the joints where the cracks showed. 

Since you have moistened the wall (stuff I have used in the past required moistening the walls before application), I would not worry.  If the cracks show up again, you might find you need to dig out about 1/4" to 3/8" into the original mortar joints.  I real PITA if doing by hand.  Even worse if you use a power saw.  Lotsa dust.  Anyway, don't worry about that problem for now.  You seem to have done the right things.

If you find it necessary to coat the walls again, and do the digging out of joints, there are expansion grouts that can be used to repoint the joints and they will never crack again unless you have a major support problem at footing level or from outside pressure. 

I am not telling you all of this to make your problem look worse than it is.  Just that i have been down that road before a few times in the nearly 40 years i was a mason contractor.  At this stage, just continue with moisture control and you really should have no problems.  Don't spend time looking for new cracks.  If all is well, new cracks probably won't show during your lifetime.  Atleast, not during my lifetime.
Tinker

 

[SteveD]

Thanks,
The cracks and holes were where blocks had been laid with insufficient mortar in spots or part blocks to make up a layer. Nothing structural. Some of the holes were big enough for large cockroaches to get in. Since the cement washing I have not seen a single roach (or even ants - who seem to get through almost invisible cracks).
It will have plenty of time to dry as I have another project to finish, some vacation and then I plan go to IWF. Hopefully I can then resume the prep work I need to do.
SteveD

 

[Tinker]

Thanks,
The cracks and holes were where blocks had been laid with insufficient mortar in spots or part blocks to make up a layer. Nothing structural. Some of the holes were big enough for large cockroaches to get in. Since the cement washing I have not seen a single roach (or even ants - who seem to get through almost invisible cracks).
It will have plenty of time to dry as I have another project to finish, some vacation and then I plan go to IWF. Hopefully I can then resume the prep work I need to do.
SteveD

Looks like a DIY'er did the block work.  If there are holes on the inside, there are holes on the outside.  Don't forget, concrete blocks are usually hollow.  The roaches are likely in there inspite of your cement covering.  They will look for a new route.

Is earth backfilled or otherwise piled against the outside of the blocks. You could have worse problem. Have you inspected for termites?  Any place south of the Mason-Dixon (and that includes Bermuda) is open territory for them.

I have relatives in Florida who bought a new house (Speculation development type).  The termites actually broke thru the concrete floor. Sounds far fetched to me, but they swear it to be a true story.

Sorry to be such a spoil-sport, but bugs can be a serious problem in a house, no matter what your climate.  Better to find them before they find you.

Tinker