Mr Mastic · South East, London and Scotland
Sand mastic for sash and case windows
Traditional burnt sand mastic renewed around sash and case windows and doors in stone and brick, for a finish that suits a period home.
- Old sand mastic that has cracked, crumbled or fallen out
- Gaps between timber frames and stone or brick
- Silicone used on a period window that looks wrong
What sand mastic for sash & case windows involves
Sand mastic is the traditional way to point the gap between a timber window frame and the stone or brick around it. It’s a mix of sand and a linseed-oil-based binder, built up in the joint and finished to look like part of the masonry. On period and listed homes it looks right where silicone wouldn’t. We rake out the old mastic, prepare the joint and renew it by hand.
We work across the South East, London and all of Scotland from our base in Crawley. Every job comes with our one-year guarantee, and we’re fully insured and an ARBOMaster approved applicator.
Problems we put right
- Old sand mastic that has cracked, crumbled or fallen out
- Gaps between timber frames and stone or brick
- Silicone used on a period window that looks wrong
- Draughts and rain around sash boxes
- Mastic that needs renewing before redecorating
Where we work
- Sash and case windows
- Stone surrounds
- Brick reveals
- Timber door frames
- Period & listed homes
- Tenement windows
How it works
- We check the window surrounds and agree which joints need renewing.
- Old, loose mastic is raked out and the joint cleaned.
- Deep voids are packed so the mastic is the right thickness.
- Sand mastic is mixed and applied by hand, then shaped to the joint.
- The finish is dressed so it sits neatly against the stone or brick.
Listed buildings and conservation areas
If your home is listed or in a conservation area, check with your local planning authority whether consent is needed for work to windows. Like-for-like sand mastic is often the preferred finish.
Sand mastic or modern sealant?
On many period windows, sand mastic looks right and suits the building. On modern frames we’d normally use a flexible sealant. We’ll talk through which suits your home.
Why it’s worth doing now
When sand mastic cracks or falls out, rain gets into the gap between the window and the stone, where it can rot the timber box and sill. Renewing it with like-for-like sand mastic keeps the weather out and keeps the window looking right for the building.
What affects the quote
We don’t publish set prices, because every job is different. Call or email us with a few details and we’ll give you a clear quote before we start. The main things that affect it are:
- How many joints, rooms, windows or metres of joint there are
- How much old sealant or grout has to come out, and how many layers
- Mould, damage or movement that needs dealing with first
- Access: stairs, height, ladders or work outside
- The product the joint needs (sanitary, exterior, fire-rated, glazing or sand mastic)
- For commercial sites, working hours and phasing
What a good quote includes
- All the old sealant removed, not sealed over
- The product named for each joint
- How long the guarantee is and what it covers
- How long before the area can be used
- How your home or building will be protected
- Who is doing the work, and that they’re insured
Aftercare
Check the mastic when you check the paintwork. Keep sills clear so water runs off, and get cracked or missing sections renewed before the timber behind them gets wet. Traditional guidance is not to paint over sand mastic, so ask us before decorating.
What customers say
Rated 4.9 on Google from 180+ five-star reviews. Read the reviews on Google.
“Called for a bathroom reseal and the mastic man showed up on time with all the right equipment. Brilliant attention to detail. The sealant looks perfect and they kept everything tidy.”
“We had old mastic that needed replacing throughout our kitchen and bathrooms. The mastic man professional was knowledgeable, quoted fairly, and delivered excellent quality work. Highly recommend!”
“Professional mastic man service from start to finish. They assessed the work properly, gave a clear quote, and executed the job perfectly. Very satisfied with the results.”
Sand mastic for sash and case windows: common questions
What is sand mastic?
A traditional pointing material made from sand and a linseed-oil-based binder, used between timber frames and stone or brick.
How long does sand mastic take to go off?
It skins over fairly quickly but takes longer to harden fully. We’ll tell you what to expect for your job.
Should sand mastic be painted over?
Traditional guidance is not to paint over sand mastic. If you’re redecorating the window, ask us about timing and finishing before you start.
Is the work guaranteed?
Yes. Every job comes with our one-year guarantee.
Do you give a price before you start?
Yes. Call or email us with a few details and we’ll give you a clear quote, so you know the price before any work starts.
Are you insured?
Yes. Mr Mastic is fully insured, and we’re an ARBOMaster approved applicator.
Page updated 26 October 2026
Near you
We cover the South East, London and Scotland. Find sand mastic for sash & case windows in your town:
- London
- Crawley
- Brighton
- Guildford
- Chelmsford
- Colchester
- Southampton
- Reading
- Oxford
- Edinburgh
- Glasgow
- Aberdeen
- Dundee