re-pointing chimney in low temps

bubbler

I've contracted a company to re-point my chimney, they are saying that the work should be complete in a day, and they expect to start in late October. It's possible we may have freezing temps overnight by then.

Is there any concern with having them perform this work in lower temps?

The chimney is in the sun during the day, so it does heat up even with low temps. In addition we have a oil fired boiler that stays up to the temp 24/7 for domestic hot water, so I would imagine that keeps the chimney itself fairly warm inside.

They are also applying ChimneySaver, I haven't read the instructions on that, but I assume it will also be OK to apply over new mortar and in October (30-50*F) temps?

Arkitexas

In commercial construction installation of masonry work is not permitted when the temperature is below 40 degrees and falling unless steps are taken to prevent freezing. You could wait until spring or make the mason responsible for maintaining minimum temperatures until the mortar sets. On large jobs that may include wrapping the work with poly and introducing a stream of warmed air into the envelope but this seems excessive for your project. Mortar setting time depends on temperature and humidity levels. At 80 degrees mortar sets in 1 to 3 hours. At 40 degrees it sets in 8 to 10 hours. Pointing work dries faster than new wall work because there is less volume and the repair is near the surface, consequently these times will be shorter. If the amount of work is small, you and the mason may prefer to gamble that it doesn't freeze. I recommend that you require the mason guarantee to repair the work if it fails.

I have never used ChimneySaver but the manufacturer's data sheet says to apply 72 hours after pointing work, at 40 degrees or higher, and allow to dry 2 to 6 hours (without freezing).
http://www.chimneysaver.com/datashee..._datasheet.pdf

concretemasonry

The classic mistake people make is to refer to the air temperature. The controlling factor is the temperature of the structure AND the temperature of the materials used. If the base material is above freezing (which is common because of the latent heat from periods before) and the materials are warm and workable, just covering should be adequate since cement materials created heat of hydration once they are in contact with mixing water.

The commercial, arbitrary standard relating to air temperature is for easy to measure and back up by the weather bureau, it does not address the real conditions to address for protection and the time required (obviously not 28 days since that only applies to lab testing and not the real world.

Just to show the fault with air temperature as a criteria, I was on a site that had about 3 weeks of -20F minimums where the frost depth was arbitrarily 5'. On a morning with -52F, after digging down through a foot or so of snow, it was discovered that the ground was no frozen below 6".

The previous exposure of the structure and temperatures of the materials control far more than a measly 25F on a cool morning. Protection does wonders.

Dick

bubbler

Thanks Arkitexas ... this actually is bringing up a few different things that I've been wondering about--how can it be a 1 day job if they are repointing and water sealing? Unless he knew he would have to return a couple of days later for the water sealing.

I haven't spoken to them specifically, but the work is scheduled for the last weekend in October. Last night the low was ~39*F, while it may get warmer there is certain no gaurantee of that, and it could easily be in the 30s that week.

I had a few estimates done and one of them did tell me that re-pointing work may need to be delayed until spring, but I think that was an attempt to get me to agree to the work on the spot.

When I call to confirm the appointment I'm going to ask two specific questions:
1) Is there any issue with the repointing/recrowning if the temperature outside is in the 30s/40s? And do you guarantee that work for any specific length of tme?

2) Do you intend to apply the water sealant the same day or come back to apply it days later after the repointing is set?

bubbler

So my thinking is that if the temperatures at night for the day or two prior to the work have been in the 40s, I'm probably just fine. If by some oddity they happen to be in the low 30s I should start to be concerned--possibly asking them to cover with a plastic would be sufficient? (I know you didn't say plastic, I'm just wondering what protection would entail)

This chimney does get full sun starting at about noon, and as I mentioned the oil burner runs fairly consistently, it also would be running even more if the outside temps are in the 30s.

stuart45

Use hessian sacking to cover up at night.