greenhouse: gap-sealing advice please

**Hilary B** · 09-10-2010, 09:45 AM

If you can (or can get someone else to) mix a pretty stiff cement mix (remember that the more you mix it the softer it gets), put a strip of wood along just inside the gap, another one a couple of inches clear OUTSIDE the gap, so that the space under the edge is 'contained', then ram your stiff cement mix into the gap as firmly as possible, squidging it enough to get most air out, then just leave it alone until it seems set, at which point you can take the wood away. Job done!
If the cement mix is sloppy, it will make a lot of mess and not do the job very well.

**Caro** · 09-10-2010, 09:51 AM

Where we had gaps (admittedly mainly near where the floor slabs met) we used that expanding foam stuff

**Hilary B** · 09-10-2010, 09:56 AM

Originally posted by Caro View Post

Where we had gaps (admittedly mainly near where the floor slabs met) we used that expanding foam stuff

My Surveyor husband would like to see that stuff banned! (but it might be OK for the purpose under discussion) We see it used in places it really doesn't belong.

**bigt1888** · 09-10-2010, 10:26 AM

two sheds can you post a pic to give a better idea of the issue?

**Bigmallly** · 09-10-2010, 11:45 AM

Originally posted by Caro View Post

Where we had gaps (admittedly mainly near where the floor slabs met) we used that expanding foam stuff

I was going to suggest the same but you beat me to it. Just fill the gap with the foam, let it set then cut any excess of with a sharp blade.

**chris** · 09-10-2010, 12:32 PM

I instantly thought expanding foam too. Just don't over fill the gap, it really does expand a lot! Then just cut off with a sharp knife/saw once dry.

**chris** · 09-10-2010, 12:33 PM

Oh didn't read BM's reply! Sorry

**Two_Sheds** · 09-10-2010, 01:37 PM

Originally posted by Hilary B View Post

... leave it alone until it seems set, at which point you can take the wood away.

Ah! So you don't cement the wood to the slabs then

Glad I asked now, thank you

Originally posted by Caro View Post

we used that expanding foam stuff

No, it's disgusting! It's all over our new window where the guy never came back to finish it off properly

Originally posted by bigt1888 View Post

two sheds can you post a pic to give a better idea of the issue?

Will do, later on

**PAULW** · 09-10-2010, 02:24 PM

I have my greenhouse on a base made of blocks that are on their edge, rather than on the slab base, just increase the thickness of cement that you sit the block on at the dipping corner.

**jackie j** · 09-10-2010, 03:34 PM

Dare I say we used ready to use postcrete, just add water, might not be what you need though, you can get other ones that are almost instant. No mixing like with concrete etc.

**bearded bloke** · 09-10-2010, 08:29 PM

Or you could do the same as me,nip down to your local timber merchant & ask them to cut you a couple of "firring`s",basically a "firring" is a log slow taper wedge that would placed on top of the flat joists on a "flat" roof to give it a fall for rain to clear.Just give them the length & ask for 1" to nothing cut from "tannalised" timber,remember you will also need a piece the width of greenhouse 1" thick,for the low end

**Two_Sheds** · 12-10-2010, 08:56 PM

I bought some quick drying cement today. There was also mortar, and concrete. What's the difference?

**bearded bloke** · 12-10-2010, 09:14 PM

Originally posted by Two_Sheds View Post

I bought some quick drying cement today. There was also mortar, and concrete. What's the difference?

Presumably it is purely cement as there is no mention of aggregate

This is a mix of sand & cement (quick drying or ordinary portland) normally used for brick laying or floor screed depending on sand type)

This is a mix of ballast & cement (quick drying or ordinary portland) normally used for footings/paving there are various sizes of ballast depending on the task
Normal choice 20mm down or 10mm down

EDIT: Reading back I see you have a gap approx 25mm at it`s thickest,building (soft) sand sould only be used in thickness of 12mm so you would ideally need to do it in two goes,sharp sand however can be used upto 75mm in a single layer

**bigt1888** · 12-10-2010, 09:30 PM

if it is just cement you would need to add sand and aggregate (pea gravel max 10mm) and water and shutter it between timbers placed at either side of the gap as described earlier in the thread. (1part cement to 3parts sand and 4 parts aggregate) and add water a little at a time to keep the mix stiff so it is easier to work with

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greenhouse: gap-sealing advice please

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