Grout under base plate without pre-wetting

[sdz]

I work in telecommunications where filed staff have to install small base plates for various things. I have talked to them and they prefer to use a flowable cementitious grout, non-shrink of course, that they can mix in small quantities. These always seem to require extensive pre soaking of the substrate and I'm sure this never gets done; they've told me so. Is there some way to fix this? A grout that doesn't require pre soaking, a primer that eliminates pre soaking?

Wish list for grout
- Flowable, non shrink
- Small batching quantities
- No pre-soaking
- nom 20mm grout thickness

 

[Ingenuity]

For cementitious grouts we SSD (saturated, surface-dried) the existing concrete then apply the flowable grout to pre-built 'grout boxes', complete with chamfer strips and polyurethane sealant to seal the base of the forms (to avoid grout leakage) prior to grout application. Finished product for exposed applications looks like this:

 

[KootK]

@SDZ: are your loads small enough to be handled with levelling nuts and no grout at all?

@Inginuity: that is one sexy grout base. Any issues with air pockets?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ingenuity]

Any issues with air pockets?

Typically no, for small plates if the grout has the right consistency and good idea is to use a small margin trowel to 'consolidate' the grout through the top 4 sides adjacent to the chamfer strips.

Always hammer-sound the base plate after grout hardens to check for presence of gross voids.

For large-plate area grouting where cementitious grouting is problematic (eg recent one was a large crusher sub-frame that was 10'x3') using epoxy resin of thickness not exceeding 1/2" that was injected using a crack injection plural pump.

 

[darthsoilsguy2]

That grout job in the photo really makes the concrete member below it look like shoddy work.

 

[Ingenuity]

That grout job in the photo really makes the concrete member below it look like shoddy work

True. But the original concrete dates back to 1950 and it is a frame to an aggregate crusher for a quarry so it gets used and abused.

The new steel column has only 2 anchor bolts - did not meet OSHA rule but somewhat common in non-buildings.

 

[sdz]

Thanks for your comments everyone.

@KootK, loads are small generally but then so are the base plates and anchors. In many cases we probably don't even need grout, but that can also be said for most plates in general. One issue is that we are often working on round tanks and sloping concrete roofs so omitting grout probably won't work. We need grout to level and align the base plate.

I am inclined to think if we could find a flowable epoxy that we could batch in small quantities, less than 1 litre, then that would be a good solution. Did I also mention many are on rooftops in full sun so the grout has to be stable at temperatures of say 60 deg C? That could also be a problem for a lot of epoxies.

 

[Ingenuity]

I am inclined to think if we could find a flowable epoxy that we could batch in small quantities, less than 1 litre, then that would be a good solution. Did I also mention many are on rooftops in full sun so the grout has to be stable at temperatures of say 60 deg C? That could also be a problem for a lot of epoxies.

A few things to consider with epoxy resins:

1. Need to make sure the forms to the base plate are sealed well with sealant or other. The viscosity of flowable resin is such that it with otherwise leak from your forms.

2. Epoxy exposed to sunlight (UV) will discolor and go chalky over time. But, usually the exposed portion of base plate grouting is very small.

3. Glass transition temp of epoxy is typically greater than 160F (72C). You can get resins with higher heat-deflection temps that may be more applicable in you case.

4. With epoxy resins on some thickness you need to consider the exothermic reaction and reduced pot life. For thick grouting operations we usually pre-place 8mm (3/8") oven-dried basalt aggregate then flood grout the baseplate after forms are sealed etc. The use of aggregate reduces the epoxy resin volume by approx 50% ($ saved) and also the exothermic effects. The aggregate acts as a heat sink.

5. Consider plastic lining the inside face of your forms. Otherwise you will have a form well adhered to the cured epoxy.

I personally would use a cementitious based dry-pack grout in your application. You may need to make the gap between the top of concrete and underside of plate is say 25mm so you can effectively dry pack it with a hammer and wood rod etc.

Where are you located? Lots of sun and high temp, I guess.

Good luck.

 

[sdz]

@Ingenuity, Tropical Queensland, Air temperatures can easily exceed 40 deg C in summer. How hot can a base plate in the sun get? I have seen a reference saying asphalt pavement in Pheonix can reach 172 F/78 C so I think that is achievable for a base plate. (

http://road.yue366.com/archives/480.html)

Can cementitious grout be used without pre-wetting? Can we paint with a sealant of some sort prior to grouting?