Mastic

[Craig]

Hi all

My architect has specified mastic on our drawings for making a seal around external doors/window frames where they abut the brickwork.

What is mastic (other than the resin from atype of conifer used in confectionery)? Is it just used as modern shorthand for a silicone selant? I dont want to use any silicone so what is the traditional alternative? Is it grouting with lime putty or linseed putty?

All advice welcomed as I am due to send the drawings out today!

Thanks
Craig

 

[RobT]

Hi Craig,

take a look at Womersleys & telephone for advice on its application etc. See link & schroll down the page:

http://www.womersleys.co.uk/acatalog/stone_repair.html

I also believe that Biff Vernon has some experience with traditional mastics and he may be able to provide some further more 'hands on' & DIY advice.

I'd also be very interested in some feedback on its application as there are many of us who could do with re-sealing our windows and exterior doors.

regards

Rob

 

[Ian Bond]

Hi Rob

I've been buying ready-made trowelling mastic from my local builders' merchant. The stuff I used comes in 5 and 10 kg tubs, and is stone coloured- just looks and smells like sand and linseed oil to me.

It's branded as Evostik Vallance Trowel Mastic and costs about £27 for 10kg.

The stuff from Womersleys appears to be the burnt sand with the linseed oil packaged separately, so you can mix fresh batches up as needed. I'm not sure how the volume / weight compares but it's >10 litres for £20, so it looks cheaper.

I've never seen 'burnt sand' sold elsewhere, and it's not something I'd have the time or inclination to try and make myself. However, now I know it's easily available it sound like a much better option then the ready mixed tubs!


Ian

 

[RobT]

Hi Ian,

just for the record, & based upon a search from the forum archive, it appears that the sand in a traditional mastic is burnt to achieve a required colour.

I suppose in theory this should allow you to colour match the surrounding stonework?

regards

Rob

 

[Ian Bond]

Sounds good to me, Rob.

I suppose if you burn the sand yourself you can control the resulting colour?

Around my way, the tradition seems to have been to paint the mastic to match the window frame. That is before the tradition became to replace all the windows with uPVC units- I don't think the fitters are making their own mastics nowadays!!!

Cheers

Ian

 

[biffvernon]

Happen I was talking to Mark Womersley about this very stuff just last week. When you said

What is mastic (other than the resin from atype of conifer used in confectionery)?

you weren't so far out. The mastic is sand, linseed oil and rosin, which I believe comes from a Portugese pine tree.

I just use fine sand and linseed oil but I expect the rosin makes it all set a bit quicker. It takes months to go hard without the rosin.