The Brew Cabin

I mortared the upper level of my new flagstone patio last weeked. The pieces were not very large (around half a square meter) and it was not easy.

Next up I need to mortar the lower level which is five times larger. Also, I used larger flagstones, with some of the pieces being as large as 1.25 square meters, and require two fit men to move. Here's a pic of the lower level (obviously a work in progress, and I have a few more pices to cut):

http://www.mrmayer.com/dsc00786.jpg

So, are there any tips on how to do set these stones in mortar? I think that it might be impossible for us to lift them up once they are down in the mortar. We had to do that twice on the upper level and I do not want to have to do that with these larger stones. It might not even be possible.

Also, my wife just came back from a tile store and they wanted her to buy this sealer that costs &#36250 (~170 quid) per gallon. That does not seem right.

Any advice?

I used to have a Chinese puzzle game that looked a bit like that patio!

When you say that you need to 'mortar', what do you mean exactly? Do you mean bed the pieces of stone, joint them, or both?

If it were my job, and the stone was being laid onto wet morrtar, I'd screed out a bed using a short length of timber, and try to set the level just fractionally higher than 'spot on', say 3-5mm high. By screeding the bedding, you ensure that you've got even coverage and that there are unlikely to be any voids once the flag is in place. Ripple the top of the screeded bed using the stick or a trowel, so that there's room for the mortar to adjust itself to any uneveness in the base of the flag when it's placed.

Once all that's done, get a couple of handy lads to lift the flagstone gently into place and tap it down using a small rubber hammer (a "clonker", as we call them in Culcheth). Check for any wobble, and if necessary, lift and re-bed.

One problem with laying larger pieces of thin flagstone or slate onto a wet mortar bed is that it can be difficult to lift the stone free of the mortar if adjustments are needed, as there is a tremendous suction created with a wet mortar. However, if you have a couple of lengths of 10-12mm steel bar, these can be slid under the offending flag and used to lever up the stone from beneath, so that there is much less chance of straining your back or breaking the flagstone.

Getting the bed right on the first attempt is, obviously, the best way to proceed, but, when you're working with a naturally variable product such as stone or slate, the best you can do is guess. Your guesses become more experienced with practice, and my dad, now almost 70 and into his 6th decade of flag laying, now gets the bed right almost every time!

I can't comment on the rpice of the sealant as I don't know what prices are like over there. 170 quid for 25 litres of a top quality sealant is not unusual in Britain, I have to say, but, to be honest, I wouldn't be thinking about sealing that stonework until the spring. I prefer to give the mortar a chance to exude all the efflorescence, and to make sure there's no movement or problems. Is it normal to seal flagstones in your part of the world?

Thank you for your great advice (again)!

I'm trying to bed the flags in mortar. I was thinking that the correct thing would be to joint the flags with a similar colored (slightly darker than the flags) grout. The flags are going on top of a 2.5cm thick layer of concrete that we poured about a month ago.

The size of the main level is around 185 square meters.

The 170 quid was for only 4 liters (actually less than 4 as I'm talking a US gallon), not 25 as you mentioned.

I live about 30 minutes from Aspen, the ski town, and our property is around 6000 meters in elevation. So the sun is a lot closer and we normally get 8-9 meters of snow over the winter months. I hear different stories about sealing. Some say let it wear naturally. Some say seal early and seal often (annually) and some say seal every three years. Some say seal before grouting, others say seal after grouting.

Personally I have not seen what unsealed flags looks like after, say, a few years. My guess is that they would deteriorate significantly if they were not sealed. I do not know when to seal, how often or what is the preferred type of sealer. I'm not a huge fan of the high-gloss finish look.

In any case, I get so many opinions and they are all completely different, which baffles me. I would think that there would be a basic way that these kinds of things are done, with "general rules of the road" to be followed. I'm not sure that is reality, though.

As always, your sage advice is appreciated. Now if I can just keep Old Man Winter away for another week I might have a chance to wrap this project up..



(Edited by MrMayer at 9:01 pm on Nov. 4, 2003)

Would the idea of using banding straps work for flags? It certainly made laying kerbs a lot easier, and the straps just slide out once the levels are right (or you can just cut them off and leave them in situ).

I think that using a darker mortar to joint the flags is a good idea. In my opinion, a bright mortar distracts the eye from the stone, which is, after all, the supposed focus of a patio, whereas a dark moratr shrinks into the background, drawing no attention to itself, while 'framing' and accentuating the flags themselves.

I don't know what to recommend regarding the sealant. Personally, I think 'varnished' looking flags are awful and so, if I am ever asked to recommend a sealant, I opt for one of the 'invisible' types that have no obvious effect on the surface of the stone. However, some folk like the 'wet look' as it does empahsise the colouring of the stone.

This is further complicated because I have no idea of which sealants are used in your country, how they interact with the stone, and what effect the elevation and weather in Aspen has on the paving over the longer term. If all of your neighbours' patios are sealed, then that would suggest that it is a received wisdom that sealing, somehow, improves the performance and longevity of the stone. With a laminar stone, the repeated freeze-thaw cycle would be catastrophic, but it may be that the stone you're using is non-laminar or is, in effect, "frost proof" - I simply don't know.

I think I would be tempted to seek out a satin or matte finish selant, or see if there are any that have no discernible effect on the appearance of the stone. I know that one of the better quality sealants used with native British stone is manufactured by Dow, which is, I beleive, a US-ian company, so they must have summat similar over there!